الجامعة اإلسالمية غزة
عمادة الدراسات العليا
كلية الهندسة
قسم الهندسة المدنية
البنية التحتية
Islamic University of Gaza
High Studies Deanship
Faculty of Engineering
Civil Engineering Department
Infrastructure
Modified stepped solarstill for brackish water
desalination
تعديالت مقترحة على المقطر الشمسي ذي العتبات لتحلية المياه المالحة
Prepared by
Ismail Amin Abu Hassaneen
Supervised by
Dr. FahidKh. Rabah
A Thesis Submitted In Partial Fulfillment of The Requirements for The Degree
of Master of Science In Civil-Infrastructure.
October 2015
II
"بسم هللا الرحمن الرحيم"
وَ مَحْيَايَ وَ مَمَاتِي لِلَّه رَبْ ونُسُكِيقُلْ إِنَّ صَالَتِي
الْعَالَمِنيَ
(261سورة األنعام )
III
ABSTRACT
Solar still is a simple solar device used for converting the available brackish or waste
water into potable water. This device has many advantages like, easily fabricated from
locally available materials and cheap maintenance with low skilled labor. A lot of works
were undertaken to improve the productivity of the still. Throughout the review on solar
still performance, the results indicated that, the basin water depth is considered one of
the main parameter that affects the still performance. Also the research showed that;
the solar still cover with inclination equal to latitude angle receives sun rays close to
normal sun rays throughout the year. The still productivity also increases with
decreasing the cover thickness and increasing its thermal conductivity. The still basin
material plays an important role in improving the productivity of the still. The research
also showed that, the daily production of still was greatly enhanced by using sponge
cubes, fins and stepped. The coupling of a solar collector, hot water tank, glass cover
cooling, external reflector, internal condenser and internal reflector increased the
productivity. Finally; from the previous efforts it was clear that; Maximum distillate
water achieved in the still was 6.670 L/(13 hrs (7:00 am to 20:00 pm))) by using stepped
solar still with pre-heating water and glass cover cooling.
In conclusion, this system proved to be promising and can be future developed to
achieve better results as well as Gaza Strip suffers from electrical energy shortage and
provide desalinated water with less price during catastrophes, wars and remote areas
with low population.
Key words: Solar still, desalination, stepped solar still, brackish water.
IV
الدراسةملخص
تعد الخلية الشمسية وسيلة بسيطة تستخدم لتحويل المياه الجوفية والعادمة الى مياه مقطرة، وهذه الطريقة
لها مزايا عديدة حيث انه يسهل تصنيعها من مواد متوفرة محليا، كما انه يسهل صيانتها مع قليل من الجهد.
هذه الخلية الشمسية، واظهرت أداءل متابعة من خالل هذا البحث قمت ببعض االعمال والتحسينات من خال
لية الخ إنتاجيةالنتائج ان عمق الماء يعد واحد من اهم المؤثرات التي تعمل على زيادة اإلنتاجية، كما أن
إلنتاجااظهر البحث أن أيضاتتزايد مع تقليل سمك الماء وزيادة التوصيلية الحرارية للغطاء في القاع،
د بشكل كبير باستخدام المقطر الشمسي ذي العتبات والمحاط باإلسفنج والمتصل بجهاز اليومي للخلية يتزاي
التكثيف، كما ان استخدام المقطر الشمسي ذي العتبات المتصل بمزود للمياه الساخنة والغطاء الزجاجي
.اإلنتاجيةأيضاالمبرد والعواكس الداخلية والخارجية تزيد من
صباحا .ساعة من 31لتر/) 676.6الحصول عليه من المياه المقطرة هي الذي تم األقصىوقد كان الحد
مساءا( عبر تسخين الماء المغذى وتبريد طبقة الزجاج الخارجي. 8وحتى
النائية قمناطفي ال هليتم استغالل في الختام أثبت هذا النظام انه واعد ويمكن تطويره لتحقيق نتائج أفضل
الكوارث والحروب. وإدارةطة وفترات انقطاع التيار الكهربائي ذات الكثافة السكانية البسي
V
DEDICATION
This research is dedicated to:
My Father and Mother for their love pray, and
continuous sacrifices…
My dear wifeHelen,myson Al Braa Ben Malek.
To all my brothers Said, Moath, Khaled, Osama
and my sister Enas.
To all my friends and colleagues…
VI
ACKNOWLEDGEMENTS
First, all praises and glory are due to ALLAH for all the bounty and support granted to
me. This work would not be done without God's endless guidance and support.
I would like to take this opportunity to sincerely thank all individuals who have helped
me in this effort. Primarily, I would like to thank my supervisor and mentor Dr.
FahidKh. Rabahfor his unlimited guidance, encouragement, and support. I am really
indebted to this man for his valuable advice and his vision which inspired this research.
Of course, this work could not be accomplished without the help of MEDRC which
was the donor for my Master.
Additionally, I would like to extend my acknowledgement to Mr. Said Nassar Mayer
of Municipality of Deir Al Balah. I forward my special thanks to Eng. Hisham Dirawi
from Municipality of Deir Al Balah, Eng. Alaa Abu Hassaneen from UNRWA and
also for Eng. Ahmad Baraka from Palestinian Water Authority for his support and
encouragement.
I would like to express my grateful appreciation and thanks to everyone who gave me
support to bring this research into reality especially to my friends.
VII
TABLE OF CONTENT
I ................................................................................................................................. إقرار
ABSTRACT ................................................................................................................. III
III .......................................................................................................................... الخالصة
DEDICATION .............................................................................................................. V
ACKNOWLEDGEMENTS ......................................................................................... VI
TABLE OF CONTENT ............................................................................................. VII
LIST OF TABLES .................................................................................................... VIII
LIST OF FIGURES ...................................................................................................... X
LIST OF ABBREVIATIONS ...................................................................................... XI
1INTRODUCTION ....................................................................................................... 1
1.1 Background .............................................................................................................. 1
1.2 Problem Statement ................................................................................................... 2
1.3Justification of the Study .......................................................................................... 3
1.4Aim and Objectives................................................................................................... 3
1.5Research Methodology ............................................................................................. 3
2LITERATURE REVIEW ............................................................................................ 5
2.1 Introduction .............................................................................................................. 5
2.2 The need for solar Desalination ............................................................................... 5
2.3 Direct desalination system ....................................................................................... 5
2.3.1 Solar humidification dehumidification desalination ............................................ 5
2.3.2 Solar chimney ....................................................................................................... 6
2.3.3 Solar still ............................................................................................................... 6
2.3.3.1 Solar still coupled with sponge cubes ................................................................ 7
2.3.3.2 Solar still coupled with sun tracking .................................................................. 7
2.3.3.3 Solar still coupled with flat plate collector ........................................................ 8
2.3.3.4 Solar still coupled with evacuated tube collector ............................................. 8
2.3.3.5 Solar still coupled with internal and external reflector ...................................... 9
2.3.3.6 Solar still coupled with condenser ................................................................... 10
2.4 Indirect desalination systems ................................................................................. 11
2.4.1 Non-membrane processes ................................................................................... 11
2.4.1.1 Solar multi stage flash desalination ................................................................. 11
VIII
2.4.1.2 Solar multi effect distillation ........................................................................... 11
2.4.1.3 Vapor compression desalination ...................................................................... 12
2.4.2 Membrane processes ........................................................................................... 12
2.4.2.1 Solar powered reverse osmosis desalination.................................................... 12
2.4.2.1.1 Solar PV powered RO desalination .............................................................. 12
2.4.2.1.2 Solar thermal powered RO desalination ....................................................... 12
2.4.2.2 Solar powered electro dialysis (ED) ................................................................ 13
2.5Techniques used to improve the performance of the solar still .............................. 13
2.5.1Basin construction materials ................................................................................ 13
2.5.2Insulation.............................................................................................................. 13
2.5.3 Vacuum technology ............................................................................................ 14
2.5.4 Wick .................................................................................................................... 14
2.5.5 Glass cover cooling ............................................................................................. 14
2.5.6 Inclination of cover ............................................................................................. 15
2.5.7 Different trays depth, width and shape ............................................................... 15
2.6 Heat transfer mechanisms in a solar still ........................................................... 16
2.7 Modes of heat transfer in a solar still ................................................................. 17
2.7.1 Internal heat transfer ................................................................................... 17
2.7.1.1 Convection heat transfer ..................................................................... .17
2.7.1.1.1 Radiation heat transfer .................................................................. 18
2.7.1.1.2 Evaporation heat transfer ............................................................. .19
2.7.1.1.3 External heat transfer .................................................................... 20
2.7.1.2 Top loss heat transfer. .......................................................................... 20
2.7.1.2.1 Bottom and side loss heat transfer ............................................... .21
2.7.1.2.2 Calculation of yield and thermal efficiency .................................. 23
2.7.1.3 Energy balance ..................................................................................... 23
2.8 Monthly optimum inclination of glass cover with internal and top external
reflector ........................................................................................................................ 24
2.9 Monthly optimum inclination of glass cover with bottom external reflector .... 26
2.10 Comparative study ............................................................................................ 27
3 MATERIALE AND METHOD ................................................................................ 29
3.1 Introduction ........................................................................................................ 29
3.2 Materials ............................................................................................................ 29
IX
3.2.1 Apparatus .................................................................................................... 29
3.2.1.1 Fabricated Conventional solar still ...................................................... 29
3.2.1.2 Fabricated Stepped solar still ............................................................... 30
3.2.3 Evacuated solar water heater ...................................................................... 31
3.2.4 Temperature device ..................................................................................... 32
3.2.5 Glass cover .................................................................................................. 33
3.2.6 The brackish water tanks ............................................................................ 33
3.3 Physical-chemical properties of inlet water sample ........................................... 33
3.4 Method ............................................................................................................... 34
3.4.1 Experimental Design ................................................................................... 34
3.4.2Analytical Method ....................................................................................... 40
3.4.3water quality................................................................................................. 41
4RESULTS AND DISCUSSION ................................................................................ 43
4.1 Effect of using conventional and steeped solar still without modification on the
performance of solar still ............................................................................................. 43
4.2 Effect of using different water depth on steeped solar still ............................... 44
4.3 Effect of using internal mirror on steeped solar still.......................................... 45
4.4 Effect of using external and internal mirror on steeped solar still ..................... 46
4.5 Effect of using glass cover cooling on steeped solar still .................................. 47
4.6 Effect of using pre heating water on steeped solar still ..................................... 48
4.7 Effect of using pre heating water with glass cover cooling on steeped solar still
...................................................................................................................................... 49
4.8 Effect of water glass temperature on productivity ............................................. 50
4.9 Accumulated productivity of the stepped solar modification ............................ 51
4.10Cost evaluation.................................................................................................. 52
5 CONCLUSION AND RECOMMENDATION ....................................................... 55
5.1 Conclusions ........................................................................................................ 55
5.2 Recommendations .............................................................................................. 56
References .................................................................................................................... 57
Appendix ...................................................................................................................... 62
X
LIST OF TABLES
Table2.1: Optimum reflector inclination for each glass covers inclination throughout
the year. ..................................................................................................................... 26
Table 2.2: Physico-chemical properties of inlet water sample .................................. 27
Table2.3: Illustrates the method used for the analysis of the required parameter ..... 28
Table 3.1: The results water samples before and after distillation with drinking water
standereds ………………………………………………………….…………..……34
Table 3.2: The results brine samples after one, two, three distillation dayes ............ 40
Table 3.3: The cost for the best fabricated Stepped still per m2 ............................... 53
Table A.1: Calculation Results Sheet No. 1 of Appendex A. .................................. 59
Table A.2: Calculation Results Sheet No. 2 of Appendex A. .................................. 60
Table A.3: Calculation Results Sheet No. 3 of Appendex A. .................................. 61
Table A.4: Calculation Results Sheet No. 4 of Appendex A. .................................. 62
Table A.5: Calculation Results Sheet No. 5 of Appendex A. .................................. 63
Table A.6: Calculation Results Sheet No. 6 of Appendex A. .................................. 64
Table A.7: Calculation Results Sheet No. 7 of Appendex A. .................................. 65
Table A.8: Calculation Results Sheet No. 8 of Appendex A. .................................. 66
Table A.9: Calculation Results Sheet No. 9 of Appendex A. .................................. 67
XI Page MS.c Thesis- I. Abu Hassaneen
LIST OF FIGURES
Figure 1.1: Cost of RO desalination Plant. .................................................................... 2
Figure 1.2:Annual variation in solar radiation in the Gaza strip.................................... 3
Figure 1.3: Research methodology steps ....................................................................... 4
Figure 2.1: Solar still with sponge. ................................................................................ 7
Figure 2.2: Schematic diagram of a simple sun tracking mechanism............................ 8
Figure 2.3:Solar still coupled with flat plate collector. .................................................. 8
Figure 2.4:Schematic diagram of evacuated tube collector. .......................................... 9
Figure 2.5:Reflected sunrays from vertical and inclined external reflectors on the
basin liner in winter. ...................................................................................................... 9
Figure 2.6: Reflected sunrays from vertical and inclined external reflectors onthe
basin liner in summer. .................................................................................................. 10
Figure 2.7: Solar still with external condenser. ........................................................... 10
Figure 2.8:Single wick still .......................................................................................... 14
Figure 2.9: The stepped solar still with film cooling ................................................... 14
Figure 2.10:(a) surface of flat type solar still, (b) absorber surface of convex type solar
still, (c) absorber surface of concave type solar still. ................................................... 15
Figure 2.11:Schematic of energy flow in a single basin single slope solar still. ......... 16
Figure 2.12:Daily amount of distillate of NRS varying with glass cover Inclination
throughout the year at 30_N latitude ........................................................................... 24
Figure 2.13:Daily amount of distillate of IS varying with glass cover Inclination
throughout the year at 30_N latitude ........................................................................... 24
Figure 2.14:Daily amount of distillate ......................................................................... 25
Figure 3.1:locally fabricated Conventional still........................................................... 29
Figure 3.2:locally fabricated Stepped solar still .......................................................... 30
Figure 3.3: tray of fabricated Stepped solar still .......................................................... 30
Figure 3.4:Evacuated solar water heater ...................................................................... 31
Figure 3.5: (LM35) temperature device ....................................................................... 31
Figure 3.6:water tanks .................................................................................................. 32
Figure 3.7:Sketch for first set which done on 20/07/2015 ........................................... 33
Figure 3.8:Sketch for second set which done on 20-23-25/07/2015 ........................... 34
Figure 3.9:Sketch for third set which done on 25/07/2015 and 05/08/2015 ................ 35
Figure 3.10:Sketch for fourth set which done on 25/07/2015 and 29/08/2015 ........... 36
Figure 3.11:Sketch for fifth set which done on 25/07/2015and 07/08/2015................37
XII Page MS.c Thesis- I. Abu Hassaneen
Figure 3.12:Sketch for sixth set which done on 25/07/2015 and 02/08/2015............38
Figure 3.13:Sketch for seventh set which done on 25/07/2015and 09/08/2015 .......... 38
Figure 4.1:Produced distillate water of conventional and stepped solar still .............. 43
Figure 4.2:Produced distillate water of different stepped solar still depth .................. 44
Figure 4.3:Produced distillate water with and without internal mirror on stepped solar
still................................................................................................................................ 45
Figure 4.4: Produced distillate water with and without internal and external mirror on
stepped solar still.......................................................................................................... 46
Figure 4.5:Produced distillate water with and without glass cover cooling on stepped
solar still ....................................................................................................................... 47
Figure 4.6: Produced distillate water with and without pre heating water on stepped
solar still ....................................................................................................................... 48
Figure 4.7: Produced distillate water with using pre heating water and glass cover
cooling on stepped solar still........................................................................................ 49
Figure 4.8: Effect of water–glass temperature difference on productivity .................. 50
Figure 4.9:Effect of water–glass temperature difference on productivity. .................. 51
Figure 4.10:Cumulative variation of fresh water productivity per unit area for all
experiments. ................................................................................................................. 52
Figure 4.11:The average cost of distillated water for different types of solar still and
my best distilled project. .............................................................................................. 54
XIII Page MS.c Thesis- I. Abu Hassaneen
Nomenclature: Symbols 𝐴 Area.
𝐴𝑎 Aperture area of solar collector.
Ab Area of basin of the solar still.
𝐴𝑐 Area of solar collector.
𝑏 Width of the still.
𝑑𝑡 Time interval.
εeff Effective emittance between water mass and glass cover.
ℎ Heat transfercoefficient.
hb The heat transfer coefficient between basin liner and the atmosphere
through the insulation.
hc,w−gi Convective heat transfercoefficient betweenwatermassandglasscover
innersurface.
he,w−giEvaporative heat transfer coefficient between water mass and glass cover
inner surface.
ℎ𝑡,𝑤−𝑔𝑖The total internal heat transfer coefficient between water mass and glass
cover inner surface.
ht,go−aThe total top heat loss coefficient between glass cover outer surface and
atmosphere.
hr,go−aThe radiative heat transfer coefficient between glass cover outer surface
and the surrounding .
hr,w−giRadiative heat transfer coefficient between water mass and glass cover inner
surface.
hw The convective heat transfer coefficient from basin liner to the water.
𝐼(𝑡) Intensity of solar radiation.
𝐼𝑒𝑓𝑓 Effective solar radiation.
𝑘 Thermal conductivity.
𝑘𝑓 Thermal conductivity of humid air.
𝑙𝑏 Length of basin.
𝑙𝑚 Height ofexternalreflector.
𝑙𝑠 The step length.
𝑚 Mass per unit basin area.
XIV Page MS.c Thesis- I. Abu Hassaneen
𝑚𝑒𝑤 Hourly yield from solar still.
𝑃 Saturated partial pressure.
𝑃𝑎 Atmospheric pressure.
𝑃𝑑 Partial pressure of vapor at dew point temperature.
𝑃𝑤 Partial vapor pressure at water surface temperature.
qb The rate of conduction heat transfer between basin liner and the atmosphere.
qc,w−g Convective heat transfer rate inside the solar still.
qcd,gi−goThe rate of conductive heat transfer from glass cover inner surface to the
glass cover outer surface.
qc,go−aThe convection heat loss from glass cover outer surface of the solar still to the
Atmosphere.
qe,w−giThe rate of evaporative heat transfer between water mass and glass cover
inner surface.
qt,go−aThe total top heat loss is the summation of convective and radiative heat
Losses.
qr,go−aThe radiation heat loss from glass cover outer surface of the solar still to the
Surroundings.
qr,w−gi Radiative heat transfer rate between water and glass cover inner surface.
qw The rate of convective heat transfer between basin liner and the water mass.
Qloss The heat losses by convection through the basin base and sides to the ground
and surrounding.
t Time.
𝑇 Temperature.
Ta Ambient temperature.
Tb Basin liner temperature.
Tw Water temperature.
Tgi Glass cover inner surface temperature.
Tg out Glass cover outer surface temperature.
Ub The overall bottom heat loss coefficient between water mass and atmosphere.
Ubs The total bottom and side heat loss coefficient from water mass to atmosphere.
Uss The overall side heat loss coefficient between water mass and atmosphere.
XV Page MS.c Thesis- I. Abu Hassaneen
𝑤 The tray width.
Greek
𝛼 Solar altitude angle.
𝛾 Solar azimuth angle.
𝜃𝑠 Tilt angle of the glass cover.
σ Stefan Boltzmann constant.
εEmissivity.
ΔTTemperature difference.
Abbreviations ED Electro dialysis.
ETCs Evacuated tube collectors.
FPCs Flate plate collectors.
SP Solar pond.
MED Multi effect distillation.
MVC Mechanical vapor compressor.
RO Reverse osmosis.
WHO World Health Organization.
NRS Internal nor the external reflectors.
ISOne with an internal reflector only.
3 Page MS.c Thesis- I. Abu Hassaneen
1INTRODUCTION
1.1 Background
Water is essential to sustain life, and a satisfactory (adequate, safe and accessible)
supply must be available to all. Improving access to safe drinking water can result in
tangible benefits to health. Every effort should be made to achieve a drinking water
quality as safe as practicable. Safe drinking water, as defined by the World Health
Organization (WHO) standard, does not represent any significant risk to health over a
lifetime of consumption, including different sensitivities that may occur between life
stages. Access to safe water represents one of the most important basic human needs of
the Palestinian people and is vital to a growing economy and a healthy population. The
quality of the pumped groundwater is the main concern ( WHO, 2008).
Desalination, Vapor compression, Reverse osmosis (RO) and Electro dialysis (ED) are
being used to provide freshwater from saline water. But the cost of energy consumption
of these methods is high. On the other hand availability of energy in remote areas and
most arid regions is low. Solar desalination is a solution for these problems ( Esfahani et
al., 2011).
Stepped solar still is an eco-friendly, small scale, cheap equipment which utilizes the
natural solar energy and is the best solution to purify water. Potable water can be
produced by the solar still at a reasonable cost. Solar desalination is the solution for
purifying the impure water in remote locations. It is the suitable method to purify water
where there is only saline water and ample amount of solar energy is available ( Ayoub
et al., 2014).
The various factors affecting the productivity of Stepped solar still are solar intensity,
wind velocity, ambient temperature, water glass temperature difference, free surface
area of water, absorber plate area, temperature of inlet water, glass angle and depth of
water. The solar intensity, wind velocity, ambient temperature cannot be controlled as
they are metrological parameters. Whereas the remaining parameters can be varied to
enhance the productivity of the solar stills ( Omara et al., 2014).
2 Page MS.c Thesis- I. Abu Hassaneen
The high incident solar radiation in the Gaza strip encourages the local manufacture
and vendor to start deal with solar desalination technology. Therefore, this paper
presents the testing results of an attempt to design and manufacture a Stepped solar still
connect with Evacuated tube collectors (ETCs), internal and external reflectors with
optimal inclination to get high productivity of distilled water.
1.2 Problem Statement
Water scarcity in the Gaza Strip forms a real crisis for people in this area. For the Gaza
strip the only source of natural freshwater is the coastal aquifer, which suffer from rapid
decline in both quality and quantity.
To face this problem, the citizens and the authority in the Gaza Strips use many options;
the major of these options is water desalination where the Reverse osmosis (RO)
technology, which needs electricity, is applied.
Energy cost in desalination plants comprises about 30% to 50% of the total cost of the
produced water based on the type of energy used. Therefore, the total cost of
desalination can be reduced significantly by reducing the energy consumption. The
following figure 1.1 shows approximate vision about the cost details for any RO plant
(Ghali et al., 2010).
Figure 1.1 Cost of RO desalination Plant (Ghali et al., 2010).
This system proved to be promising and can be future developed to achieve better
results as well as Gaza Strip suffers from electrical energy shortage and provide
desalinated water with less price during catastrophes, wars and remote areas with low
population.
1 Page MS.c Thesis- I. Abu Hassaneen
1.3Justification of the Study
The Gaza strip is semi-arid as well coastal region. Solar insulation in the Gaza strip is
relatively high. The daily average solar radiation on horizontal surface is about 222
W/𝑚2 (7014 MJ/𝑚2/yr). The following Figure 1.2 illustrates the variation in the daily
average, in the total insulation on horizontal surface for each month (Alaydi,2011).
Figure 1.2 Annual variation in solar radiation in the Gaza strip ( Alaydi, 2011).
Therefore we intended to utilize the natural sources of brackish water, sea water and
high solar radiation in development of appropriate, household-scale water purification
technology.
1.4Aim and Objectives
This study aims to make a development of small scale solar desalination technology in
the Gaza strip, by using local market materials to enhance the productivity of distilled
water to face electricity problems and shortage of good water quality.
The objectives of this research are to investigate the performance of a stepped solar still
by:
Adding wick on the vertical sides.
Supplying preheated water into the solar still.
Using trays with constant depth and width.
Using internal and external reflectors.
Using glass cover cooling.
1.5Research Methodology
Methodology consists of eleven stages. The first stage is the research concept, search
for optimum design of Stepped solar still, this comes from reading literature, paper and
several books. The second stage is to design a Stepped solar still prototype for enough
4 Page MS.c Thesis- I. Abu Hassaneen
for household. The third stage is to search in the market for selected material. Forth
stage was to the fabricate the design Stepped solar still, after locally fabrication the
Stepped solar still. Fifth stage is to make primary testing of the fabrication. After
primary testing sixth stage is to add some extra modification were added on the design
and change some of the selected materials. After adding modification and changing
materials, The seven stage is to make primary testing on the locally modified solar still.
The eight stage is to start experiments on the modified Stepped solar still. The ninth
stage was to calculate on the collected data by Excel sheet figures. Tenth stage started
to have results and discussions from Excel sheet figure. Finally stage number Eleven is
to make conclusion and recommendations. Figure 1.3 shows research methodology
steps.
Figure 1.3 Research methodology steps
5 Page MS.c Thesis- I. Abu Hassaneen
2 LITERATURE REVIEW
2.1 Introduction
Desalination technologies have been used for about a century in land-based plants and
on ships to provide water for a crew. The regular use of desalination technologies
accelerated after World War II, as the demand for fresh water in arid countries. The
cost for desalination has been decreasing rapidly, especially in recent years with the
introduction of efficient, more cost effective technologies. For solar distillation
systems, sunlight has the advantage of zero fuel cost but it requires more space (for its
collection) and generally more costly equipment. In principle, the water from a solar
still should be quite pure. The slow desalination process allows only pure water to
evaporate from the basin and collect on the cover, leaving all particulate contaminants
behind. A solar still is a simple device, which can be used to convert saline, brackish
water into drinking water. Solar stills use exactly the same processes, which in nature
generate rainfall, namely evaporation and condensation. Its function is very simple a
transparent cover encloses a pan of saline water ( kabeel et at., 2010).
2.2 The need for solar desalination
All the water treatment processes use a large amount of energy to remove a portion of
pure water from a salt water source. Salt water (feed water) is fed into the process, and
the result is one output stream of pure water and another of waste water with a high salt
concentration. Large commercial desalination plants using fossil fuel are in use in a
number of oil-rich countries to supplement the traditional sources of water supply.
Other countries in the world have neither the money nor oil resources to allow them to
develop in a similar manner and because of this energy demand and high cost of plants,
we prefer solar energy for the desalination process ( Murugavel, 2013).
2.3 Direct desalination system
2.3.1 Solar humidification dehumidification desalination
The main idea behind the solar humidification–dehumidification process is that the
moisture carrying capacity of the air increases with the increase in temperature. When
hot air heated by solar collector circulated in natural or forced mode comes in contact
with saline water which is sprayed in the evaporator, a certain quantity of vapor is
6 Page MS.c Thesis- I. Abu Hassaneen
extracted by the air which could be recovered by condenser where saline feed water is
preheated. Four types of humidification–dehumidification desalination configurations
are closed air, open water cycle; closed air, closed water cycle; open air, open water
cycle and open air, closed water cycle. There always exists an optimum mass flow rate
ratio of water to dry air for maximum thermal energy recovery rate for a given spray
water temperature and condenser water temperature and the thermal energy recovery
rate could be increased by increasing the number of stages ( Sharon and Reddy, 2015).
2.3.2 Solar chimney
Solar chimney converts solar thermal energy into kinetic energy which in turn is
converted into electrical energy using turbo generator. The main components of solar
chimney are large diameter solar collectors, turbine, generator and long chimney.
Collectors used are mainly glass or plastic sheet which act as greenhouse, trapping heat
and causes the earth below the collector to get warmed up resulting in temperature
difference between the ambient air and the air inside the system causing heated air to
flow through the chimney. The kinetic energy of the moving air causes rotation of
turbine mounted below the chimney to produce power ( Sangi, 2012).
2.3.3 Solar still
The simple solar still is the oldest and most basic, low-tech desalination system
currently in use, and many improvements have been suggested over the years to
improve its efficiency. In essence, solar stills mimic the natural distillation process off
the hydrological cycle that generates rainfall: evaporation and condensation. In all solar
stills, a transparent cover (typically glass or plastic) encloses a basin of saline water. As
the sun shines through the glass, water heats up to a boil, causing evaporation and
condensation on the inner surface of the transparent cover. The distillate produced is of
very high quality, as all salts and other inorganic and organic components remain in the
basin, and pathogenic bacteria are killed in the boiling process. Modifications of the
solar still, including the basin still, wick still, and diffusion still, increase the thermal
efficiency of a simple still by at most 50%, and so were also regarded as impractical for
the purpose of this project ( Qiblawey and Banat , 2008).
2.3.3.1 Solar still coupled with sponge cubes
A solar pond (SP) is a thermal solar collector that includes its own storage system. A
solar pond collects solar energy by absorbing direct and diffuse sunlight. Therefore,
. Page MS.c Thesis- I. Abu Hassaneen
sponge cubes in the saline water was used to improve the evaporation rate as shown in
Figure 2.1 ( Velmurugana and Sritharb , 2007).
Figure 2.1 Solar still with sponge ( Velmurugana and Sritharb , 2007).
2.3.3.2 Solar still coupled with sun tracking
A Sun Tracking mechanism is a device incorporated into a solar still which follows the
movement of the sun across the sky with the aim of ensuring that maximum solar
irradiance is transmitted through the glass cover of the still into the basin and is
absorbed by the brine from sunrise to sunset, throughout the day as shown in figure 2.2
,The sun tracking mechanism is grouped into two types, the single axis and the double
axis models. The single axis is usually on a horizontal axle or vertical axle depending
on the region of use and application. The horizontal is used in the tropics where the sun
is very high at midday, but with shorter days while the vertical is used in high latitudes
where the sun is slightly high, but with very long summer days. The double axis sun
tracking mechanism has both a horizontal and vertical axle so, can be deployed
anywhere in the world
Figure 2.2A schematic diagram of a simple sun tracking mechanism
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2.3.3.3 Solar still coupled with flat plate collector
Flat-plate collectors (FPCs) are used as heat transfer fluid, which circulates through
absorber pipes made of either metal or plastic. The absorber pipes are assembled on a
flat plate and they usually have a transparent protective surface in order to minimize
heat losses. FPCs is integrated with the solar still, to increase the temperature of the
basin water. The preheated water from the solar collector was circulated by a tube
through the basin water. The tube is acting as a heat exchanger and exchanging heat
from the preheated water to the basin water. Thus the basin water gets heated. In an
another arrangement, as shown in Figure 2.3, the basin water is directly circulated
through the flat plate collector ( Qiblawey and Banat, 2008).
Figure 2.3 Solar still coupled with flat plate collector ( Qiblawey and Banat, 2008).
2.3.3.4 Solar still coupled with evacuated tube collector
Heat losses are minimized in evacuated tube collectors (ETCs) by an evacuated cover
of the receiver. This cover is tubular and made of glass. In addition, a selective coating
of the receiver minimizes the losses due to infrared radiation. There are two different
technologies of evacuated tubes: (1) Dewar tubes two coaxial tubes made of glass,
which are sealed each other at both ends; and (2) ETC with a metallic receiver, which
requires a glass to metal seal ( Kalogirou, 2005).
The evacuated tube solar collector (ETC) has more advantageous than the flat plate
collectors for water heating purposes. The evacuated tubes greatly reduce the heat
losses as vacuum is present in the tubes as shown in Figure 2.4 , It consists of two
coaxial tubes with evacuated space between an outer surface of inner tube and inner
surface of outer tube. A selective coating is applied to the outer surface of the inner
tube. The heat transfer fluid enters through small diameter delivery glass tube and exits
9 Page MS.c Thesis- I. Abu Hassaneen
from the same end of the tube through annular space between delivery tube and
selective coated absorber tube. The annular space between selectively coated tube and
borosilicate outermost glass tube is evacuated to minimize the convection loss from the
selective surface ( Sampathkumar et at., 2010).
Figure 2.4 Schematic diagram of evacuated tube collector ( Sampathkumar et at., 2010).
2.3.3.5 Solar still coupled with internal and external reflector
Internal and external reflectors can increase the distillate productivity of solar stills,
useful and inexpensive modification to increase the distillate productivity of solar stills.
Because of the usage of reflectors, more solar radiation is introduced into the still
compared to other solar stills and thus increment in the daily productivity ( Omara et al.,
2014).
In winter, the altitude angle of the sun decreases so a consider able amount of the
reflected radiation from a vertical external reflector would escape to the ground without
hitting the basin liner. Therefore, the reflector should be inclined slightly forward to
absorb the reflected sunrays on the basin liner effectively as shown in Figure 2.5 the
reflector in winter ( Tanaka , 2010).
Figure 2.5 Reflected sunrays from vertical and inclined external reflectors on
the basin liner in winter (Tanaka , 2010).
36 Page MS.c Thesis- I. Abu Hassaneen
On the other hand, the altitude angle of the sun increases in summer and the vertical
external reflector cannot effectively reflect sunrays to the basin liner. So the external
reflector should be inclined slightly toward the back as shown in Figure 2.6 reflector in
summer( Tanaka , 2010).
Figure 2.6 Reflected sunrays from vertical and inclined external reflectors on
the basin liner in summer ( Tanaka , 2010).
2.3.3.6 Solar still coupled with condenser
Condenser is attached with a solar still as shown in Figure 2.7 to enhance the
productivity of the solar still. The condensation occurs due to the temperature
difference not only on the glass surface but also on the four sidewalls, which can be
cooled by water circulation through tubes attached on the wall surface for efficiency
enhancement ( Velmurugan and Srithar , 2011).
Figure 2.7 Solar still with external condenser ( Velmurugan and Srithar , 2011).
2.4 Indirect desalination systems
2.4.1 Non-membrane processes
In non-membrane desalination process, the heated feed water is allowed to evaporate
in distillation units to produce water vapors which are condensed using condenser to
produce distillate. The distillate produced is of high quality and the rate of distillation
33 Page MS.c Thesis- I. Abu Hassaneen
can be enhanced by incorporating vacuum. In this process temperature of feed water,
condensing surface and pressure plays an important role in distillate yield.
2.4.1.1 Solar multi stage flash desalination
In multi stage flash desalination system, the feed saline water is heated above the
saturation temperature in brine heater and is made to flash in the vessel where low
pressure is maintained using vacuum pump. The brined is charged from the previous
stage is allowed to flash in successive stages and the vapors formed in each stage is
condensed using condenser where inlet saline water is preheated
2.4.1.2 Solar multi effect distillation
Multi effect distillation (MED) unit consists of vessels which are generally called
effects maintained successively at low pressure where saline water is sprayed. The heat
required to cause evaporation in first effect is supplied by solar energy or by combustion
of fossil fuel and the vapors thus formed are used to heat the feed in the next effect.
Thus, the latent heat of the produced vapors in the previous effects are successfully
utilized for the next effect in MED. MED systems are gaining more market share
because of its better compatibility with solar thermal desalination ( Mezher et. at, 2011).
2.4.1.3 Vapor compression desalination
In vapor compression desalination, the feed saline water heated by external heat source
is allowed to flash, the vapors thus produced are compressed using mechanical vapor
compressor (MVC) or thermo vapor compressor (TVC) to raise the condensation
pressure and temperature of the vapor and the compressed vapor is used to heat the
same stage or feed water of other stages (Sharon and Reddy, 2015).
2.4.2 Membrane processes
In membrane process, fresh water is produced from saline water by allowing passage
of water molecules (in case of reverse osmosis) or ions (in case of electro dialysis)
through membranes by applying high pressure (above osmotic pressure) or electrical
potential.
2.4.2.1 Solar powered reverse osmosis desalination
Reverse osmosis (RO) is a pressure driven desalination process in which pressurized
feed water is allowed to pass through the cross flow membrane module. If the applied
pressure is higher than the osmotic pressure, fresh water permeates across the
32 Page MS.c Thesis- I. Abu Hassaneen
membrane and it is collected through the permeate tube and the brine is drained out (Greenlee, 2009).
2.4.2.1.1 Solar PV powered RO desalination
In solar PV powered RO unit, the power required for the desalination process is
supplied by photovoltaic panels and the system can be operated with (or) without
batteries, Solar PV operated reverse osmosis unit has better socio-economic and
environment benefits compared to diesel generator operated reverse osmosis unit (
Eltawil .et al , 2008).
2.4.2.1.2 Solar thermal powered RO desalination
In solar thermal powered RO desalination, the mechanical energy produced by the solar
organic cycles is directly used to run the high pressure pumps of RO unit(Penate, 2012).
The solar thermal driven RO desalination unit is a more promising technology, any
development in RO technology would be useful for developing RO technology based
on solar thermal systems.. The unit cost of water produced by RO plant could be
reduced by using hybrid solar assisted steam cycle for supplying required shaft power
for RO high pressure pump ( Eltawil .et al , 2008).
2.4.2.2 Solar powered electro dialysis (ED)
Electro dialysis (ED) is the process of removal of salts from saline water and the ED
unit consists of large number of compartments filled with saline water and separated by
cation and anion exchange membranes. When DC polarity is applied across the cathode
and anode, the negative ions passes through the anion exchange membrane and positive
ions passes through the cation exchange membranes and these ions gets accumulated
in a particular compartment and is discharged out as brine. Reversal of polarity is
usually followed every 20 min to prevent deposition of salts in the membranes. The
solar powered ED desalination system is suitable for (a) areas having less or no electric
power, (b) areas with no access to low cost fuel supply and
(c) areas with abundant sunshine ( Charcosset, 2009).
2.5Techniques used to improve the performance of the solar still
Researchers have taken efforts to make different designs of solar still for higher
distillate yield and inferred that solar stills are effective and efficient.
31 Page MS.c Thesis- I. Abu Hassaneen
2.5.1Basin construction materials
Solar radiation that passes through the transparent cover is absorbed by saline water
and the basin liner of a solar still. So, the basin liner acts as an absorber of solar radiation
and it is important for the liner to have a relatively high absorbance for solar radiation,
basin liners can be made of plastic or metal-sheet. Some plastics are relatively cheap
while others are expensive. Common metal sheets applied in solar collection are copper,
aluminum and steel . The important property of a metal for application in solar
engineering is thermal conductivity. Copper and aluminum have relatively high thermal
conductivities ( Murugavel .et al, 2014).
2.5.2Insulation
Thermal insulation is the simplest way to prevent heat losses and to achieve economy
in energy usage especially in solar thermal systems. Thermal insulation serves many
significant functions such as, to conserve energy, to reduce heat loss or heat gain, to
maintain an efficient operation of the system (or chemical reaction), to assist in
sustaining a product at a constant temperature, to prevent condensation, to create a
comfortable environmental, to protect personnel. Conventional insulation materials are
often opaque and suitably classified into, fibrous, cellular, granular and reflecting types
materials. Some commonly used thermal insulation materials are as; glass, fiber,
alumina silicate, mineral wool and calcium silicate ( Saxena et al , 2015).
2.5.3 Vacuum technology
The effect of vacuum inside the still is to avoid any heat transfer due to convection in
the still. The heat loss from the water in an insulated still is due to evaporation and
radiation only. In the presence of vacuum, the effect of the non-condensable gas, which
reduces the rate of condensation, was also avoided ( Velmurugan and Srithar , 2011).
2.5.4 Wick
Wick still mostly come under inclined type still. In a wick still, the feed water flows
slowly through a porous, radiation-absorbing pad (the wick). Two advantages are
claimed over basin stills. First, the wick still can be tilted so that the feed water presents
a better angle to the sun. It reduces reflection and presents a large effective area. Second,
less feed water is in the still at any time and so the water is heated more quickly and to
a higher temperature. The main disadvantage in this still is while cloud passing or after
sunset, it does not produce distillate. However, in the case of basin still the productivity
34 Page MS.c Thesis- I. Abu Hassaneen
continuous for some time due to heat stored in the basin water, the figure 2.8 shows
Single wick still ( Kumar.et al, 2015).
Figure 2.8 Single wick still ( Kumar.et al, 2015).
2.5.5 Glass cover cooling
To increase the performance of the stepped solar still outlet water film cooling is
recycled as a makeup water, as shown in figure 2.9 .It was found that film cooling
thickness, volumetric flow rate, and water film inlet temperature have a significant
effect on the daily distillate productivity. The presence of the glass cover water film
cooling may increase the stepped still daily productivity by about 8.2% but the value of
this percentage mainly depends on the combinations of film cooling parameters. On the
other hand, the presence of the film cooling neutralized the effect of air wind speed on
the still distillate productivity ( Kabeel et at., 2015).
Figure 2.9 The stepped solar still with film cooling ( Kabeel et at., 2015).
2.5.6 Inclination of cover
The yield from a solar still heavily relies on the tilt angle of the solar glass. This angle
in turn depends on inclination and the direction the cover is facing, and also its latitude.
It is expected that covers that has an inclination that is aligned with the angle of the
35 Page MS.c Thesis- I. Abu Hassaneen
latitude will be the recipient of a normal solar radiation annually. This is deemed as
important due to the fact that evaporation is reliant on intensity of solar radiation. This
leads to the adjustment of the angle of inclination with respect to the solar azimuth
angle and solar intensity (Muftah et al, 2014).
2.5.7 Different trays depth, width and shape
Depth of water in the solar still inversely affects the productivity of the solar still.
Investigations indicated that a reduction of the brine depth in the still improves the
productivity, mainly due to the higher basin temperature. For maintaining minimum
depth, wicks, plastic water purifier and stepped solar still were used. So that stepped
solar stills can increase the distillate productivity about conventional solar stills, many
reports studied the performance of stepped solar still ( Abdullah , 2013).
The figure 2.9 shown different absorber surface of stepped solar still such absorber
surface of flat type solar still, absorber surface of convex type solar still, absorber
surface of concave type solar still .
Figure 2.10 (a) surface of flat type solar still, (b) absorber surface of convex type solar still,
(c) absorber surface of concave type solar still ( Kabeel et al., 2015).
2.6 Heat transfer mechanisms in a solar still
Generally, a heat transfer process is broadly classified as being either steady or
transient. During steady heat transfer process, the temperature or heat flux remains
unchanged with time, but in transient process these properties are time dependent. Most
of the heat transfer processes encountered in practice are transient in nature. The
36 Page MS.c Thesis- I. Abu Hassaneen
transient heat transfer processes are difficult to analyze, but they could be analyzed
based on some presumed steady conditions. The heat transfer in a solar still is
considered as the transient heat transfer process due to the variation in temperature or
heat flux with respect to time. Figure 2.10 shows the energy flow that take place inside
as well as outside of the single basin single slope solar still during the desalination
process ( Elango .et al, 2015).
Figure 2.11 Schematic of energy flow in a single basin single slope solar still.
2.7 Modes of heat transfer in a solar still
The heat transfer process in a solar still can be broadly classified into internal and
external heat transfer processes based on energy flow in and out of the enclosed space.
The internal heat transfer is responsible for the transportation of pure water in the vapor
form leaving behind impurities in the basin itself, whereas the external heat transfer
through the condensing cover is responsible for the condensation of pure vapor as
distillate ( Elango .et al, 2015).
2.7.1 Internal heat transfer
The heat exchange between water surface and glass cover inner surface of the solar
still is known as internal heat transfer. There are three modes, namely convection,
radiation and evaporation processes, by which the internal heat transfer process within
the solar still is governed. These three modes of internal heat transfer process are
described as follows
3. Page MS.c Thesis- I. Abu Hassaneen
2.7.1.1 Convection heat transfer.
Convection heat transfer process is complicated in nature by the fact that it involves
fluid motion as well as heat conduction. The convection heat transfer strongly depends
on fluid properties and geometry and roughness of solid surface involved. In a solar
still, the convection heat transfer takes place between basin water and glass cover inner
surface across humid air due to temperature difference between them ( Elango .et al,
2015).
The convective heat transfer rate inside the solar still can be expressed in terms of water
temperature (Tw) and glass cover inner surface temperature (Tgi) by the following
relation:
qc,w−g = hc,w−gAw(Tw − Tgi) (2. 1)
In the above expression is the convective heat transfer coefficient between water mass
and glass cover inner surface and can be calculated as follows:-
hc,w−gi = 0.884 {(Tw − Tgi) +(Pw−Pgi)(Tw+273.17)
268900−Pw}
1/3
(2. 2)
The saturation vapor pressures at water temperature and glass cover inner surface
temperature are evaluated by the following expressions:-
Pw = exp (25.317 −5144
Tw+273) (2. 3)
Pg = exp (25.317 −5144
Tg+273) (2. 4)
2.7.1.1.1 Radiation heat transfer
The radiation heat transfer occurs through a mechanism that involves the emission of
internal energy of the object. The energy transfer by radiation is the fastest and it suffers
no attenuation in a vacuum. Also, the radiation heat transfer occurs in solids as well as
in liquids and gases. Even it can occur between two bodies separated by a medium
which is colder than both the bodies. The radiative heat transfer occurs at inside of the
solar still between water mass and glass cover inner surface ( Elango .et al, 2015).
38 Page MS.c Thesis- I. Abu Hassaneen
The view factor plays a major role in determining the rate of radiative heat transfer. In
solar still, the view factor is assumed as unity since the inclination of glass cover with
horizontal is small.
The radiative heat transfer rate between water and glass cover inner surface can be
obtained by the following relation:-
qr,w−gi = hr,w−gi(TW − Tgi) (2. 5)
where hr,w−gi is the radiative heat transfer coefficient between water mass and glass
cover inner surface and evaluated by:-
hr,w−gi = σεeff{(Tw + 273.15)2 − (Tg + 273.15)2}(Tw + Tg + 546) (2. 6)
The effective emittance between water mass and glass cover is given as:-
εeff = (1
εw+
1
εg− 1)−1 (2. 7)
2.7.1.1.2 Evaporation heat transfer.
Evaporation occurs at the liquid- vapor interface when the vapor pressure is less than
the saturation pressure of the liquid at a given temperature. The evaporation heat
transfer occurs in the solar still between water and water–vapor interface ( Elango .et al,
2015).
The rate of evaporative heat transfer between water mass and glass cover inner surface
is given by:-
qe,w−gi = he,w−gi(Tw − Tgi) (2. 8)
In the above expression, he,w−gi is called as evaporative heat transfer coefficient
between water mass and glass cover inner surface and determined by:-
he,w−gi = (16.237 ∗ 10−3)hc,w−gi(Pw − Pgi)/(Tw − Tgi) (2.9)
The total internal heat transfer rate is the summation of convective, radiative, and
evaporative heat transfer rates between water mass and glass cover inner surface which
is given as:-
qt,w−gi = qc,w−gi + qr,w−gi + qe,w−gi (2.10)
Also,
39 Page MS.c Thesis- I. Abu Hassaneen
qt,w−gi = ht,w−gi(Tw − Tgi) (2.11)
The total internal heat transfer coefficient between water mass and glass cover inner
surface ℎ𝑡,𝑤−𝑔𝑖 is obtained by the following expression:-
ht,w−gi = hc,w−gi + hr,w−gi + he,w−gi (2.12)
The rate of conductive heat transfer from glass cover inner surface to the glass cover
outer surface is given by:-
qcd,gi−go =Kg
Lg(Tgi − Tgo) (2.13)
2.7.1.1.3 External heat transfer
The external heat transfer consists of conduction, convection, and radiation processes
which are independent of each other. It is considered as the loss of heat energy from
the solar still to the atmosphere. The heat lose in the solar still from glass cover outer
surface to the atmosphere is called as top loss heat transfer process and from water mass
to the atmosphere through insulation is called as bottom and side loss heat transfer
process. The higher the former the higher will be the yield from the solar still and lower
the latter better will be the yield. They are described briefly in the following section
2.7.1.2 Top loss heat transfer. The heat energy from the glass cover outer surface is lost to the atmosphere by
convection and radiation heat transfer processes.
The convection heat loss from glass cover outer surface of the solar still to the
atmosphere is given by:-
qc,go−a = hc,go−a(Tgo − Ta) (2.14)
The convective heat transfer coefficient hc,go−a is expressed in terms of wind
velocity(v) as follows:-
hc,go−a = 2.8 + (3.0 ∗ V) (2.15)
The radiation heat loss from glass cover outer surface of the solar still to the
surroundings is given by:-
qr,go−a = hc,go−a(Tgo − Ta) (2.16)
26 Page MS.c Thesis- I. Abu Hassaneen
The radiative heat transfer coefficient between glass cover outer surface and the
surrounding is given as:-
hr,go−a = σεg{(Tgo + 273)4 − (Tsky + 273)4}/(Tgo − Ta) (2.17)
where
Tsky = (Ta − 6) (2.18)
The total top heat loss is the summation of convective and radiative heat losses
which is given as:-
qt,go−a = qc,go−a + qr,go−a − a (2.19)
Also
qt,go−a = ht,go−a(Tgo − Ta) (2.20)
The total top heat loss coefficient between glass cover outer surface and atmosphere
can be obtained by the following relation:-
ht,go−a = hc,go−a + hr,go−a (2.21)
The total top heat loss coefficient can also be determined directly in terms of wind
velocity (v) by considering the effect of both radiation and free convection from the
condensing cover by the following expression:-
ht,go−a = 5.7 + (3.8 ∗ V) (2.22)
2.7.1.2.1 Bottom and side loss heat transfer. The heat energy is lost from water to the atmosphere through basin liner and insulation
by conduction, convection and radiation processes. In case of solar still mounted on
stand, the bottom and side heat losses occur in sequence—first convection, then
conduction and, finally, convection and radiation losses to the ambient. But, in case of
grounded solar still, the bottom heat loss is first in the form of convection and then
conduction only (Elango .et al, 2015).
The rate of convective heat transfer between basin liner and the water mass is given
by:-
23 Page MS.c Thesis- I. Abu Hassaneen
qw = hw(Tb − Tw) (2.23)
where hw is the convective heat transfer coefficient from basin liner to the water.
The rate of conduction heat transfer between basin liner and the atmosphere is given
by:-
qb = hb(Tb − Ta) (2.24)
The heat transfer coefficient between basin liner and the atmosphere through the
insulation is:-
hb = √Lins
Kins+
1
ht,b−a (2.25)
Where
ht,b−a = 5.7 + (3.8 ∗ V) (2.26)
The overall bottom heat loss coefficient between water mass and atmosphere is given
by:-
Ub =hw+hb
hw+hb (2.27)
The overall side heat loss coefficient between water mass and atmosphere is expressed
as:-
Uss =Ass
Ab+ Ub (2.28)
The total bottom and side heat loss coefficient from water mass to atmosphere can be
given by:-
Ubs = Ub + Uss (2.29)
For lower water depth, the overall side heat loss coefficient (Uss) can be neglected since
the area of side walls losing heat (Ass) is very small compared with area of basin
(Ab) of the solar still.
The overall external heat loss coefficient from water mass to the atmosphere through
top, bottom and sides of the solar still is expressed as:-
ULS = Ut + Ubs (2.30)
22 Page MS.c Thesis- I. Abu Hassaneen
The heat losses by convection through the basin base and sides to the ground and
surrounding:-
Qloss = UbAb(Ab − As) ∗ (Tb − Ta ) (2.31)
Where Ub = Kl − Li , and Kl and Li are thermal conductivity and the thickness of the
insulation.
2.7.1.2.2 Calculation of yield and thermal efficiency
The hourly yield is given by the following equation:-
mew = he,w−g(Tb − Tg) ∗ 3600/(hfg) (2.32)
The daily efficiency,ηd, is obtained by the summation of the hourly condensate
production m, multiplied by the latent heat hfg , hence the result is divided by the daily
average solar radiation I(t) over the whole area A of the device:-
ηd =∑ m∗hfg
∑ A∗I(t) (2.33)
2.7.1.3 Energy balance
The analytical results are obtained by solving of the energy balance equations for the
absorber plate, saline water and glass cover of the solar still. The saline water
temperature, basin plate temperature and glass cover temperature can be evaluated at
every instant.
Energy balance for the basin plate:-
I(t)Abαb = mbcpb (dTb
dt) + Qc,b−w + Qloss (2.34)
Energy balance for the saline water:-
I(t)Awαw + Qc,b−w = mwcpw (dTw
dt) + Qc,w−g + Qr,w−g + Qe,w−g + Qfw (2.35)
Energy balance for the glass cover:-
I(t)Agαg + Qc,w−g + Qr,w−g + Qe,w−g = mwcpg (dTg
dt) + Qr,g−sky + Qc,g−sky (2.36)
For the stepped still with mirrors the solar radiation reflected by the mirrors per step
and absorbed by the basin (trays) and saline water can be determined as the product of
21 Page MS.c Thesis- I. Abu Hassaneen
the direct solar irradiance, the shadow area of the vertical mirror, transmittance of the
glass cover, reflectance of the mirror, 𝜌𝑖𝑛𝑡, and absorptance of the basin liner or of saline
water, and this may be expressed as:
Qint,b = I(t)τgρintαb ∗ wls tan θs cos γ/ tan α (2.37)
Qint,w = I(t)τgρintαw ∗ wls tan θs cos γ/ tan α (2.38)
Where 𝑤 is the tray width and 𝑙𝑠 is the step length, 𝛼 solar altitude angle, 𝛾 solar azimuth
angle and 𝜃𝑠 tilt angle of the glass cover.
Energy balance for the basin plate (stepped still with mirrors):-
I(t)τgAbαb + (I(t)τgρintαb ∗ wls tan θs cos γ / tan α) ∗ 9 = mbcpb (dTb
dt) +
Qc,b−w + Qloss (2.38)
Energy balance for the saline water of stepped still with mirrors:-
I(t)τgAwαw + (I(t)τgρintαw ∗ wls tan θs cos γ / tan α) ∗ 9 + Qc,b−w =
mwcpw (dTw
dt) + Qc,w−g + Qr,w−g + Qe,w−g + Qfw (2.39)
2.8 Monthly optimum inclination of glass cover with internal and top
external reflector
The daily amounts of distillate produced by a still with neither the internal nor the
external reflectors (called NRS) and one with an internal reflector only (called IS)
varying with glass cover inclination 𝜃𝑠 throughout the year at 30_N are shown in Figure
3.2 and 3.3. The daily amount of distillate produced by NRS remains almost constant
to the glass cover inclination 𝜃𝑠 in any month, while one of IS increases with an increase
in glass cover inclination 𝜃𝑠 except for in summer (May–July). This is because the effect
of the inclination 𝜃𝑠 on the amount of the absorption of direct solar radiation is
negligible, but the absorption of solar radiation reflected by the internal reflector
increases with an increase in inclination 𝜃𝑠 since the area of the internal reflector
increases with an increase in inclination 𝜃𝑠 (Tanaka, 2010).
24 Page MS.c Thesis- I. Abu Hassaneen
Figure 2.12 Daily amount of distillate of NRS varying with glass cover
Inclination throughout the year at 30_N latitude (Tanaka, 2010).
Figure 2.13 Daily amount of distillate of IS varying with glass cover
Inclination throughout the year at 30_N latitude ( Tanaka, 2010).
For a basin type still, it is difficult to change the glass cover inclination 𝜃𝑠 according to
seasons, so the actual operation for a basin type still would be done with the glass cover
angle fixed throughout the year. In this situation, the reflector inclination 𝜃𝑚 should be
adjusted to the optimum values for each month listed in Table 3.1 for a still with glass
cover inclination 𝜃𝑠 of 10–50_. Here, to facilitate ease of adjustment, inclinations 𝜃𝑠 and
𝜃𝑚 are assumed to be set at 5_ steps. The optimum combination of 𝜗𝑠 and 𝜗𝑚 to
maximize the daily amount of distillate for each month are underlined in Table 2. The
25 Page MS.c Thesis- I. Abu Hassaneen
optimum glass cover inclination 𝜗𝑠would be 10_ in summer (May, June and July) and
50_ in other seasons, and the optimum reflector inclination 𝜗𝑚 is smallest in spring
and autumn at 0_, and greatest in summer and winter at 25_ with 𝜗𝑠= 10_ in June and
𝜗𝑠= 50_ in December ( Tanaka, 2010).
Table 2.1 Optimum reflector inclination for each glass covers inclination throughout
the year ( Tanaka, 2010).
𝜽𝒔
Optimum reflector inclination 𝝑𝒎for each glass cover inclination (∘)
Jan
ua
ry
Fe
bru
ary
Ma
rch
Ap
ril
Ma
y
Ju
ne
Ju
ly
Au
gu
st
Sep
tem
be
r
Octo
be
r
No
vem
be
r
Decem
be
r
10 5 0 0 15 20 25 20 15 0 0 5 10 15 10 0 0 15 20 20 20 15 0 0 10 10 20 10 5 0 10 15 20 15 10 0 5 10 10 25 10 5 0 10 15 15 15 10 0 5 10 15 30 15 10 0 5 15 15 15 10 0 10 15 15 35 15 10 0 5 10 15 10 5 0 10 15 20 40 20 10 5 5 10 10 10 5 5 10 20 20 45 20 20 5 0 10 10 10 0 5 15 20 20 50 20 20 10 0 5 10 5 0 5 15 20 25 10 5 0 0 15 20 25 20 15 0 0 5 10
2.9 Monthly optimum inclination of glass cover with bottom external
reflector
Bottom reflector can reflect the sunrays to the evaporating wick and increase the
distillate productivity of a tilted wick still as shown in figure 3.3 when the reflector
inclination 𝜃𝑚 is larger than about 15° on spring and autumn equinox and winter
solstice, and 25° on the summer solstice ( Tanaka, 2010).
Figure 2.14 Daily amount of distillate ( Tanaka, 2010).
26 Page MS.c Thesis- I. Abu Hassaneen
2.10 Comparative study
The comparative study of performance improvement techniques used in solar stills and
their results are represented in Table 2.2
Table 2.2 The different review types and area of solar stills, climatic condition and
daylight hours ( Kabeel et al., 2010).
No. Ref. Type of solar still Climatic condition Area,m2 Daylight
hours
Fath et al. Single-slope Egypt 1.52 6-18
Samee et al. Single-slope Pakistan 0.54 10-19
Kumar and
Tiwari
Single-slope India 1 9-17
Kumar and
Tiwari
With solar collector India 1 9-17
Badran and
Tahaineh
With solar collector Jordan 1 8-18
Abdel-Rehim
and Lasheen
With solar
concentrator
Egypt 1 9-19
Abdallah and
Badran
With sun tracking Jordan 1 7-18
Fath et al. Pyramid-shaped Egypt 1.52 6-18
Al-Hinai et al. Pyramid-shaped Oman 1 8-20
Badran et al. Pyramid with collector Jordan 0.92 8-17
Velmurugan
et al.
With fin type India 1 8-17
2. Page MS.c Thesis- I. Abu Hassaneen
Velmurugan
et al.
With wick and fin type India 1 9-17
Velmurugan
et al.
Stepped with fins and
sponges
India 0.5 9-17
Table 2.3 The cost comparison of different solar still ( Kabeel et al., 2010).
No. Ref. CPL (cost of distilled
water per liter) ( $)
Fath et al. 0.035
Samee et al. 0.063
Kumar and Tiwari 0.14
Kumar and Tiwari 0.18
Badran and Tahaineh 0.115
Abdel-Rehim and Lasheen 0.058
Abdallah and Badran 0.23
Fath et al. 0.031
Al-Hinai et al. 0.0135
Badran et al. 0.103
Velmurugan et al. 0.054
Velmurugan et al. 0.065
Velmurugan et al. 0.064
28 Page MS.c Thesis- I. Abu Hassaneen
3MATERIALES AND METHODS
3.1 Introduction
The experiments were carried out in Deir El Balah, Gaza, Palestine. The location lies
at 31.68° N latitude and 34.42° E longitude. The experiments were carried out during
the period of July to August 2015 from 7:00 am to 8:00 pm, it is installed South
direction to receive maximum solar radiation throughout the year. In this work, two
solar stills were designed and fabricated to compare and evaluate the performance of
proposed solar desalination systems, and to get most efficiency and highest production
distilled water. The first one is a conventional still, the second is a stepped solar still.
3.2 Materials
3.2.1 Apparatus
3.2.1.1 Fabricated conventional solar still
The conventional still (a single basin) shown as a photo in figure 4.1 has a basin area
of 1 𝑚2 (100 cm×100 cm). High-side wall depth is 50 cm and the low-side wall height
is 20 cm. The still is made of aluminum sheets (1.5 mm thick)that consist of four
sidewalls and a bottom, it is fixed inside external body made of wood (5mm thickness).
The whole basin surfaces are coated with black paint from inside to increase the
absorptivity. Also, the still is insulated from the bottom to the sidewalls with sawdust
4 cm thick to reduce the heat loss from the still to ambient. The insulation layer is
supported by a wooden frame. The basin is covered with a glass sheet (110 cm×120cm),
3 mm thick inclined at nearly 30° horizontally, to collect the distillate output, a trough
was fixed at the end of the low-side of basin. Plastic pipe was connected to the trough
to drain the fresh water (distillate) to external calibrated flask.
29 Page MS.c Thesis- I. Abu Hassaneen
Figure 3.1 locally fabricated Conventional still.
3.2.1.2 Fabricated Stepped solar still
The Stepped solar still shown as a photo in figure 4.2 and figure 4.3 has a basin area of
1 𝑚2 (100 cm×100 cm). High-side wall depth is 110 cm and the low-side wall height
is 15 cm. The still is made of aluminum sheets (1.5 mm thick) that consist of four
sidewalls and a bottom, it fixed is inside external body made of wood (5mm thickness).
The whole basin surfaces are coated with black paint from inside to increase the
absorptivity. Also, the still is insulated from the bottom to the sidewalls with sawdust
4 cm thick to reduce the heat loss from the still to ambient. The insulation layer is
supported by a wooden frame. The basin is covered with a glass sheet (120 cm×140
cm), 3 mm thick inclined at nearly 30° horizontally. The absorber plate is made of 10
steps (each of size 10cm× 100cm) with tray depth 2mm,5mm, and 10mm and width
100cm. Integrating fins in the basin of the absorber plate on tray, the fins are made of
aluminum sheet with a height, length and breadth of 20,100 and 1 mm, respectively.
The pitch between two successive fins is taken as 100 mm and kept constant. The
mirrors added on the vertical sides of the steps as wicks as internal reflectors of stepped
still. The top external reflector inclined backward. The width and length of the external
( top and bottom ) reflector are 100cm×120cm. Two sprinklers are constructed and
installed on the top part of the glass of stepped solar still in order to ease splashing
method for cooling the glass cover with tap water with external Fan, To collect the
distillate output, a trough was fixed at the end of the low-side of basin. Plastic pipe was
connected to the trough to drain the fresh water (distillate) to external calibrated flask.
16 Page MS.c Thesis- I. Abu Hassaneen
Figure 3.2 locally fabricated Stepped solar still.
Figure 3.3 Tray of fabricated Stepped solar still.
3.2.3 Evacuated solar water heater.
The evacuated solar water heater as shown as in figure 3.4 consisted of collector, water
tank, expansion vessel and frame. The solar collector consists of 12 vacuum tubes; each
tube has 5.8 cm outer diameter, 4.8 cm inner diameter and 1.8 m length. Inside each
evacuated glass tube there is a sealed copper heat pipe running through the inner tube.
The hollow copper heat pipe within the tube is evacuated of air but contains a small
quantity of a low pressure water–ethylene glycol plus some additional additives to
13 Page MS.c Thesis- I. Abu Hassaneen
prevent corrosion or oxidation. A cylindrical stainless steel water tank having 120 l
capacity was used to feed the basin with brackish hot water through insulated tube.
Figure 3.4 Evacuated solar water heater.
3.2.4 Temperature measurement device
The temperature at various locations in the still were measured by (LM 35) as shown
in figure 3.5 coupled to digital microcontroller [its range from 10 to 130°C] the
accuracy of this device is in the range of 1.0°C for the temperature measurements
between 10 and 130°C. Five sensors were used to measure the following temperatures:
Basin, glass (in), ambient, water, and glass (out).
Figure 3.5 Temperature measurement device (LM35).
3.2.5 Glass cover
In this work window glass of 4 mm thickness was used and its average transmissivity
(t) of 0.88, it was fixed at an angel 30° with the horizontal. Glass cover has been sealed
with silicon rubber, which is the most successful because it will make strongly contact
12 Page MS.c Thesis- I. Abu Hassaneen
between the glass and many other materials. The sealant is important for efficient
operation. It is used to secure the cover to the frame, take any up difference in expansion
and contraction between dissimilar materials.
3.2.6 The brackish water tanks
Two water tanks were made of 2mm thickness of plastic, it has a diameter of 100 cm,
a height of 150 cm and its volume is 1500 l. The first water tank is located at a suitable
level from the still unit to allow saline water to flow regularly from its outlet hole (at
its bottom) through control valve to Evacuated solar water heater, the second tank is
located after solar still which storage water exterior from the still then pump it to
Evacuated solar water heater.
Figure 3.6 Water tanks.
3.3 Physical-chemical properties of inlet water sample
Brackish water samples were used in this experiment, was obtained from one of the
wells in Deir El Balah (Al Turazy well), Initial pH of the water was 7.5, which is the
original pH of water samples, each condition was tested 3 times and an average value
was reported together with its corresponding standard deviation as shown in table 3.1
11 Page MS.c Thesis- I. Abu Hassaneen
Table 3.1 Physical-chemical properties of inlet water sample from Al Turazy well.
Temperature 25 EC µS /cm 4120
pH 7.5 TDS mg/L 2616
Nitrate mg/L 128 Chloride mg/L 969
Sodium mg/L 706 Magnesium mg/L 85
Potassium mg/L 4 Alkalinity mg/L 307
3.4 Methods
3.4.1 Experimental Designs
In this research, seven sets of experiments were performed as follows:
First set: Distilled water from Conventional solar still and stepped solar still without
pre heating:-
It consists of a brackish water tank, a conventional still (single basin solar still) and a
stepped solar still as shown in figure 3.7
Figure 3.7 Sketch for first set which done on 20/07/2015 .
14 Page MS.c Thesis- I. Abu Hassaneen
Second set: Distilled water from Stepped solar still with different tray depth without
pre heating:-
It consists of a saline water tank and stepped solar stills with different tray depth 2, 5,
and 10 cm. The modified stepped solar still has the same specification and dimensions
of the first set except the stepped solar still with 5 and 10 cm tray depth did not have
fins in the basin as shown in figure 3.8
Figure 3.8 Sketch for second set which done on 20-23-25/07/2015
Third set: Distilled water from Stepped solar still with and without heating water:-
It consists of a saline water tank, a vacuum tube solar collector, two stepped solar still,
storage tank, Amorphous silicon solar photovoltaic (PV), charge controller, battery and
inverter. Two modified stepped solar still have the same specification and dimensions
of the first set with tray depth 2 cm, the first stepped solar still experimental procedure
is the same in first set, the second stepped solar still feed water from vacuum tube solar
collector which used to preheat the feed water of the saline water, the water which exist
from the still storage in tank and pumped every two hour to saline water, the pump
which rise hot water from storage tank to saline water tank connect with solar
15 Page MS.c Thesis- I. Abu Hassaneen
photovoltaic (PV), charge controller, battery and inverter which work with solar energy
as shown in figure 3.9
Figure 3.8 Sketch for third set which done on25/07/2015 and 05/08/2015
Fourth set: Distilled water from Stepped solar still with and without internal
reflectors:-
It consists of a saline water tank and two stepped solar stills. The first stepped solar still
experimental procedure is the same in first set; the second stepped solar still has an
internal reflector 10 mirrors (10 *100 cm) wicks on vertical side of steps to increase the
evaporation surface area of the water as shown in figure 3.9
Figure 3.9 Sketch for fourth set which done on25/07/2015 and 29/07/2015
16 Page MS.c Thesis- I. Abu Hassaneen
Fifth set: Distilled water from Stepped solar still with and without external reflectors:-
It consists of a saline water tank and two stepped solar stills. The first stepped solar still
experimental procedure is the same in first set; the second stepped solar still has the
same specification and dimensions of the first set except an external reflector 2 mirror
(top and bottom reflectors 100 * 120 cm) as shown in figure 3.10
Figure 3.10 Sketch for fifth set which done on25/07/2015 and 07/08/2015
Sixth set: Distilled water from Stepped solar still with and without internal and external
reflectors:-
It consists of a saline water tank and two stepped solar stills. The first stepped solar still
experimental procedure is the same in first set; the second stepped solar still has the
same specification and dimensions of the first set except an external reflector 2 mirrors
(top and bottom reflectors 100 * 120 cm) and an internal reflector 10 mirrors (10 *100
cm) wicks on vertical side of steps to increase the evaporation surface area of the water
as shown in figure 3.11
1. Page MS.c Thesis- I. Abu Hassaneen
Figure 3.11 Sketch for sixth set which done on25/07/2015 and 02/08/2015
Seventh set: Distilled water from Stepped solar still with and without external cooling
system:-
It consists of a saline water tank and two stepped solar stills and external fan. The first
stepped solar still experimental procedure is the same in first set; the second stepped
solar still has the same specification and dimensions of the first set except the cold water
flows over the glass cover was kept uniform and constant with the help of a regulator
and constant head tank . The evaporated water contacts the glass cover and condenses
then run down, and collected. Two sprinklers are constructed and installed on the top
part of the glass of stepped solar still in order to ease splashing method for cooling the
glass cover with tap water with external Fan as shown in figure 3.12 and 3.13
Figure 3.12 Sketch for seventh set which done on25/07/2015 and 09/08/2015
18 Page MS.c Thesis- I. Abu Hassaneen
Figure 3.12 Sketch for seventh set which done on25/07/2015 and 02/08/2015
3.4.2 Analytical Method
The water analysis was performed according to standard methods for the examination
of water and wastewater as shown in Table 3.2
Table 3.2 illustrates the method used for the analysis of the required parameter.
No. Parameter Method
1 EC EC-Hach ECO20 cond
2 CL- 4500 CL-B. Argentometric method
In order to evaluate the distillate water chemistry, the distillate water samples were
collected during the month of August in 2015. In all the experiments, for statistical
purposes, each condition was tested 3 times and an average value was reported together
with its corresponding standard deviation. The results water samples before and after
distillation is shown in Table 3.3 with standards given World Health Organization
(WHO). The results revealed that, all the samples were well agreed with standard values
after distillation.
19 Page MS.c Thesis- I. Abu Hassaneen
Table 3.3 The results water samples before and after distillation with drinking water
standards
No.
Paramete
r
Before
Distillation
After
Distillation
For set
no 1
After
Distillation
For set
no 2
After
Distillation
For set
no 3
After
Distillation
For set
no 4
After
Distillation
For set
no 5
After
Distillation
For set
no 6
WHO
Standard**
1 ECµS/c
m
4120 33 31 29 35 32 44 <250
2 TDSmg
/L
2616.2 16.5 15.5 14.5 17.5 16 22 <600
3 CL-
mg/L
969.7 8.5 8.5 8 9 8.5 9.5 <250
**WHO. Guidelines for drinking-water quality 4th ed. Geneva, Switzerland: World
Health Organization; 2011 [chapter 10].
3.4.3 Water quality
Little research has been done regarding the water quality of the water produced by
solar-stills based on polluted or muddy water. However it is proven that nitrates,
chlorides, iron, heavy metals and dissolved solids are completely removed by the solar
still (Al-Hayek and Badran, 2004 and Zein and Al-Dallal, 1984). The process also
proved to be effective in the destruction of microbiological organisms present in the
feed water (Al-Hayek and Badran, 2004). The distillate is thus high purity water, which
also lacks essential dissolved minerals. Drinking demineralized water can have serious
health consequences, and it is thus of crucial importance that the essential minerals are
added to the water before consumption (WHO, 2004b). The advised quantities of
minerals where minimum or no adverse health effects are observed are shown are
shown in Table 3.4
46 Page MS.c Thesis- I. Abu Hassaneen
Table 3.4 : Advised mineralogical quantities (from WHO, 2004b)
Total
Dissolve
d Solids
(mg/l)
Bicarbonat
e ion (mg/l)
Calciu
m
(mg//l)
Magnesiu
m (mg/l)
Hardnes
s
(mmol/l)
Alkalinit
y (meq/l)
Minimum 100 30 20 10
Optimum 250-500
40-80 20-30 2-4
Maximu
m
6.5
In order to evaluate the brine water chemistry. Table (3.5) shows the brine water
samples were collected after one, two and three day of experiments.
Table 3.5 The results brine samples after one, two, three distillation days.
No.
Parameter
Before
Distillation
After
On day
After
two day
After
three day
1 EC µS/cm 4120 4800 5630 6950
2 TDS mg/L 2616.2 3120 3605 4449
3 CL- mg/L 969.7 1105 1310 1590
** Not:- The results in table 3.5 for the brine sample which done on 25/07/2015 which
I must take more samples from all sets to be more scientific and to now when the brine
in the cell must pore and back wash the cell.
43 Page MS.c Thesis- I. Abu Hassaneen
4 RESULTS AND DISCUSSION
In this research the desalination characteristics of brackish water (TDS 2616 mg/l) by
conventional and modified stepped solar still were studied. The main investigated were
depth of water, internal reflector, external reflector, feed water temperature, glass cover
cooling, collector efficiency, distillate water chemistry. At the end of the experiments
and data collection, results and calculations were discussed as follows:-
4.1 Effect of using conventional and stepped solar still without modification
on the performance of solar still
Figure 4.1 illustrates comparison between the hourly variation of fresh water
productivity per unit area for stepped solar still and conventional still, respectively for
both case the feed water TDS was 2616mg/l. Data are given in Calculation sheets No.
1and 4 of Appendix A
Figure 4.1 Produced distillate water (ml/hr) of conventional and stepped solar still
It is observed from Figure 4.1 that the produced distilled water increases as the time
increase till a maximum value at noon time i.e. 14:00 pm, the produced distillate water
was equal to 520 ml/hr in stepped solar still while the produced distillate water on
conventional still was equal to 500 ml/hr , and then start to decrease after that, and the
total produced distillate water for stepped solar still was (3.060 L/(13 hrs (7:00 am to
20:00 pm))) while the total produced distillate water for conventional still was (2.835
L/(13 hrs (7:00 am to 20:00 pm))), in this case the increase in distillate production for
stepped solar still is 7.35% higher than that for conventional still. Therefore the
42 Page MS.c Thesis- I. Abu Hassaneen
produced distillate water increases with the increases of the ambient temperature and
decreases with decreases of the ambient temperature.
This phenomenon can be attributed to the fact that a smaller air volume trapped inside
the stepped solar still chamber than in the conventional still and therefore heating up
the trapped air will be much faster.
4.2 Effect of using different water depth on stepped solar still
Figure 5.2 illustrates comparison between the hourly variation of fresh water
productivity per unit area for different water depth on stepped solar still, respectively
for three cases the feed water TDS was 2616mg/l. Data are given in Calculation sheets
No. 1,2, and 3 of Appendix A
Figure 4.2 Produced distillate water (ml/hr) of different stepped solar still depth
It is observed from Figure 4.2 that the produced distilled water increases as the time
increase till a maximum value at noon time i.e. 14:00 pm, the produced distillate water
was equal to 595 ml/hr in stepped solar still with water depth 2 cm while the produced
distillate water was equal to 520 ml/hr in stepped solar still with water depth 5 cm while
the produced distillate water was equal to 500 ml/hr in stepped solar still with water
depth 10 cm, and the total produced distillate water for stepped solar still with water
depth 2 cm was (3.355 L/(13 hrs (7:00 am to 20:00 pm))), and the total produced
distillate water for stepped solar still with water depth 5 cm was (3.060 L/(13 hrs (7:00
am to 20:00 pm))), and the total produced distillate water for stepped solar still with
water depth 10 cm was (2.785 L/(13 hrs (7:00 am to 20:00 pm))). In this case the
41 Page MS.c Thesis- I. Abu Hassaneen
increase in distillate production for stepped solar still with 2 cm and 5 cm is 16.98% ,
8.98% higher than stepped solar still with 10 cm .
This phenomenon can be attributed to the fact that a reduction of water depth in the
still improves the productivity.
4.3 Effect of using internal mirror on stepped solar still
Figure 4.3 illustrates comparison between the hourly variation of fresh water
productivity per unit area for stepped solar still with and without internal mirror,
respectively for both case the feed water TDS was 2616mg/l. Data are given in
Calculation sheets No. 3and 5 of Appendix A
Figure 4.3 Produced distillate water (ml/hr) with and without internal mirror on stepped
solar still
It is observed from Figure 4.3 that the produced distilled water increases as the time
increase till a maximum value at noon time i.e. 14:00 pm, the produced distillate water
was equal to 620 ml/hr when used internal mirror while the produced distillate water
was equal to 595 ml/hr without mirror, and then start to decrease after that, and the total
produced distillate water for stepped solar still with internal mirror was (3.535 L/(13
hrs (7:00 am to 20:00 pm))) while the total produced distillate water without mirror was
(3.355 L/(13 hrs (7:00 am to 20:00 pm))), also we found wide different change between
11:00 am to 14:00 pm and narrow different change between 15:00 pm to 20:00 pm. In
this case the increase in distillate production for stepped solar still with internal mirror
was 5.09 % more than without mirror with same water depth.
44 Page MS.c Thesis- I. Abu Hassaneen
This phenomenon can be attributed to the fact that using wick increases the evaporating
surface area of the water by reflecting more solar radiation to the surface of water before
mid-day which heat water and more water evaporation and more productivity.
4.4 Effect of using external and internal mirror on stepped solar still
Figure 4.4 illustrates comparison between the hourly variation of fresh water
productivity per unit area for stepped solar still with and without internal and external
mirror, respectably for both case the feed water TDS was 2616mg/l. Data are given in
Calculation sheets No. 3and 8 of Appendix A
Figure 4.4 Produced distillate water (ml/hr) with and without internal and external
mirror on stepped solar still
It is observed from Figure 4.4 that the produced distilled water increases as the time
increase till a maximum value at noon time i.e. 14:00 pm, the produced distillate water
was equal to 640 ml/hr when used internal and external mirror while the produced
distillate water was equal to 595 ml/hr without mirror, and then start to decrease after
that, and the total produced distillate water for stepped solar still with internal mirror
was (3.890 L/(13 hrs (7:00 am to 20:00 pm))) while the total produced distillate water
without mirror was (3.355 L/(13 hrs (7:00 am to 20:00 pm))). In this case the increase
in distillate production for stepped solar still with internal and external mirror was 13.75
% more than without mirror with same water depth.
This phenomenon can be attributed to the fact that using top and bottom reflector
increases the evaporating surface area of the water by reflecting more solar radiation to
45 Page MS.c Thesis- I. Abu Hassaneen
the surface of water before and after mid-day which heat water and more water
evaporation, more glass temperature, and more productivity.
4.5 Effect of using glass cover cooling on stepped solar still
Figure 4.5 illustrates comparison between the hourly variation of fresh water
productivity per unit area for stepped solar still with and without glass cover cooling,
respectively for both case the feed water TDS was 2616mg/l. Data are given in
Calculation sheets No. 3and 6 of Appendix A
Figure 4.5 Produced distillate water (ml/hr) with and without glass cover cooling on
stepped solar still
It is observed from Figure 4.5 that the produced distilled water increases as the time
increase till a maximum value at noon time i.e. 14:00 pm, the produced distillate water
was equal to 280 ml/hr when used glass cover cooling while the produced distillate
water was equal to 595 ml/hr without modification, and then start to decrease after that,
and the total produced distillate water for stepped solar still with glass cover cooling
was (1.945 L/(13 hrs (7:00 am to 20:00 pm))) while the total produced distillate water
without modification was (3.355 L/(13 hrs (7:00 am to 20:00 pm))), and with used glass
cover cooling the productivity decreased more than without glass cover cooling after
12:00 pm to 18:00 pm. In this case the decrease in distillate production for stepped solar
still with glass cover cooling was 42.02 % more than without modification with same
water depth.
This phenomenon can be attributed to the fact that using glass cover cooling decrease
water–glass temperature difference, which decrease the evaporative heat transfer rate.
46 Page MS.c Thesis- I. Abu Hassaneen
4.6 Effect of using pre heated water on stepped solar still
Figure 4.6 illustrates comparison between the hourly variation of fresh water
productivity per unit area for stepped solar still with and without pre heating water,
respectively for both case the feed water TDS was 2616mg/l. Data are given in
Calculation sheets No. 3and 7 of Appendix A
Figure 4.6 Produced distillate water (ml/hr) with and without pre heating water on
stepped solar still
It is observed from Figure 4.6 that the produced distilled water increases as the time
increase till a maximum value at noon time i.e. 14:00 pm, the produced distillate water
was equal to 740 ml/hr when used internal and external mirror while the produced
distillate water was equal to 595 ml/hr without mirror, and then start to decrease after
that, and the total produced distillate water for stepped solar still with internal mirror
was (5.425 L/(13 hrs (7:00 am to 20:00 pm))) while the total produced distillate water
without mirror was (3.355 L/(13 hrs (7:00 am to 20:00 pm))). In this case the increase
in distillate production for stepped solar still with pre heating water was 61.69 % more
than without pre heating water with same water depth.
This phenomenon can be attributed to the fact that using hot feed water to the still
reduces the time required to raise the water temperature and increase the temperature
difference between the boiler and stepped solar still.
4. Page MS.c Thesis- I. Abu Hassaneen
4.7 Effect of using pre heated water with glass cover cooling on stepped
solar still
Figure 4.7 illustrates comparison between the hourly variation of fresh water
productivity per unit area for stepped solar still using pre heating water with glass cover
cooling and without modification, respectively for both case the feed water TDS was
2616mg/l. Data are given in Calculation sheets No. 3and 9 of Appendix A
Figure 4.7 Produced distillate water (ml/hr) with using pre heating water and glass cover
cooling on stepped solar still
It is observed from Figure 4.7 that the produced distilled water increases as the time
increase till a maximum value at noon time i.e. 14:00 pm, the produced distillate water
was equal to 710 ml/hr when used pre heating water with glass cover cooling while the
produced distillate water was equal to 595 ml/hr without modification, and then start to
decrease after that, and the total produced distillate water for stepped solar still with pre
heating water and glass cover cooling was (6.670 L/(13 hrs (7:00 am to 20:00 pm)))
while the total produced distillate water without modification was (3.355 L/(13 hrs
(7:00 am to 20:00 pm))). In this case the increase in distillate production for stepped
solar still with pre heating water and glass cover cooling was 98.80 % more than
without modification with same water depth.
This phenomenon can be attributed to the fact that when the solar still works in high
temperature by means of supplying heat to the basin, the higher evaporation rate is
achieved. Thus, the glass cover will receive more latent heat of vaporization. In turn,
the temperature of the glass cover increases, and temperature difference between the
glass cover and basin water decreases. This causes low vaporization and, thus, low
48 Page MS.c Thesis- I. Abu Hassaneen
yield. To overcome the glass overheating problem, a water cooling system was applied
to the glass acting.
4.8 Effect of water glass temperature on productivity
Figure 4.8 illustrates comparison between the hourly variations of fresh water
productivity for stepped solar still without modification against water glass temperature
difference. Data are given in Calculation sheet No.3 of Appendix A
Figure 4.8 Effect of water–glass temperature difference on productivity.
It is observed from Figure 4.8 that the for the maximum water-glass temperature
difference Tw-Tg of 21°C, productivity is 595 ml/hr and the average water-glass
temperature difference Tw-Tg of 13 °C, productivity is 400 ml/hr.
But in Figure 4.9 illustrates comparison between the hourly variations of fresh water
productivity for stepped solar still with pre-heating and glass cover cooling against
water glass temperature difference. Data are given in Calculation sheet No.9 of
Appendix A
49 Page MS.c Thesis- I. Abu Hassaneen
Figure 4.9 Effect of water–glass temperature difference on productivity.
It is observed from Figure 4.9 that the for the maximum water-glass temperature
difference Tw-Tg of 42°C, productivity is 690 ml/hr and the average water-glass
temperature difference Tw-Tg of 25 °C, productivity is 500 ml/hr.
This phenomenon can be attributed to the fact that increases in water–glass temperature
difference increases the evaporative heat transfer rate. Hence the evaporation rate
increases with higher water–glass temperature differences.
4.9 Accumulated productivity of the stepped solar modification
Figure 4.10 illustrates comparison between the cumulative variations of fresh water
productivity per unit area for all experiments. Data are given in Calculation sheet No.
1 to 9 of Appendix A
56 Page MS.c Thesis- I. Abu Hassaneen
Figure 4.10Cumulative variation of fresh water productivity per unit area for all
experiments
It is observed from Figure 4.10 that for the effect set that give the highest productivity
(6.670 L/(13 hrs (7:00 am to 20:00 pm))) by using pre-heating water with glass cover
cooling and the others sets give productivity less than 6.670 L/(13 hrs (7:00 am to 20:00
pm))).
This phenomenon can be attributed to the fact that increases in water–glass temperature
difference increases the evaporative heat transfer rate, and more consideration on
surface glass with is the same surface on all sets.
4.10 Cost evaluation
To make the solar desalination system perform well, it requires some maintenance.
Therefore the annual maintenance cost should be considered. For this system,
maintenance is required frequently due to the following reasons: (i) Continuous water
supply into the stills, (ii) replacement of broken or damaged parts, and (iii) cleaning of
solar stills, solar water heater and condenser. Cost estimation for various components
used in the solar desalination system for the best distillate system that I recommended
to use is given in Table 4.4
53 Page MS.c Thesis- I. Abu Hassaneen
Table 4.4 The cost for the best fabricated Stepped still per 𝑚2
Item
Cost ($)
Aluminum sheet 130
Support legs 30
Paint 10
Inlet sawdust's 20
Glass cover 60
Fan 30
Photovoltaic system 250
Pump 70
Tanks 100
Evacuated solar water heater 500
Plastic pipe 30
Mirrors 50
Fittings 10
Temperature measurement device 100
Welding 60
Lab test 50
Total 1500$
The total fixed cost of Stepped still per 1𝑚2 was about F=1500 $. To obtain the average
value of the cost of distillate output, it is important to assume that V is the variable cost,
C is the total cost, where, C = F + V. In Egypt the variable cost ranged is from 25 to
30% from the fixed cost. Assume variable cost V equals to 0.3 F per year, as reported
in Omara and Eltawil , and the annual variable cost includes the maintenance cost, the
expected still life time is 10 years, then: C = 1500 + 0.3 × 1500 × 10 = 6000 $ where
the average daily productivity can be estimated from the analysis of different
experimental data, and it is taken as 6.670 l/day. To determine the annual cost of 1 l
52 Page MS.c Thesis- I. Abu Hassaneen
assuming that the still operates 340 days in a year. The total productivity during the life
of Stepped still = 6.670 × 10 × 340 = 22678 l. Then the cost of 1 l from Stepped still =
6000/22678 = 0.26 $.
If we shows the average cost of distillated water for different types of solar still in
chapter 2 and my project as shown in figure 4.11
Figure 4.11 The average cost of distillated water for different types of solar still and my
best distilled project
The results obtained that my project give the maximum water production cost with 0.26
$.
51 Page MS.c Thesis- I. Abu Hassaneen
6 CONCLUSIONS AND RECOMMENDATIONS
6.1 Conclusions
In this research the desalination characteristics of brackish water by Stepped solar still
was studied. The efficiency of the system was tested by exceeding some modification
to enhance the productivity such as adding wick on the vertical sides, supplying pre
heat water into the solar still, using trays with constant width, using internal and
external reflectors, and glass cover cooling. At the end of the experiments the following
important conclusions were drawn it was concluded that:-
1. The stepped solar still (the tray width equal the step width 10cm and step
depth 5cm ) achieved about 7.35% higher productivity than the conventional
solar still with water depth 5cm.
2. The stepped solar still incorporated with solar air heater and glass cover
cooling technique productivity was increased by 98.80 % more than stepped
solar still without modification with same water depth.
3. Glass cover cooling the external surface of the stepped solar still has a bad
effect on enhancing the productivity and the efficiency of the system
decreases approximately to 42%.
4. The daily productivity of the stepped still by using wick on the vertical sides
(internal reflector) and external reflector was increased by 13.75% more
than stepped solar still without modification with same water depth.
5. Daily productivity of the stepped still by preheating the feed water of the
stepped solar still was increased by 61.69 % more than without preheating
water with same water depth.
6. The daily productivity of stepped solar still by using wick on the vertical
sides (internal reflector) was increased by 5.09% more than stepped solar
still without modification with same water depth.
7. The daily productivity of stepped solar still Increasing by decreasing water
depth from 10, 5, to 2cm with efficiency 8.98%, 16.98% higher than
stepped solar still with 10 cm .
8. Increasing in water–glass temperature difference increases the evaporative
heat transfer rate.
9. Increasing the inclination angle of the bottom external reflector from
vertical to 30° has an adverse effect on the productivity in the summer
months.
10. Increasing the inclination angle of the top external reflector from vertical to
10° has an adverse effect on the productivity in the summer months.
54 Page MS.c Thesis- I. Abu Hassaneen
11. The brine increasing in water with time of experimental which must release
after some days.
12. The results obtained that my project give the maximum water production
cost with 0.26 $.
6.2 Recommendations
1. It is recommended for future research to increase area of condensation
surface for solar distillation.
2. It is recommended for future research to find cheap components to reduce
the cost of this system in the market.
3. It is recommended for future research to mix distillated water with brackish
water without exceeding quality criteria of WHO with low cost to produce
sufficient amount of water for the residence in the same house .
55 Page MS.c Thesis- I. Abu Hassaneen
References Abdullah, A. (2013). Improving the performance of stepped solar still, vol. 319 , pp.
60–65.
Alaydi, J, Y. (2011). The solar energy potential of Gaza, vol. 11.
Ayoub, Z. M., and Malaeb, L. (2014). Economic feasibility of a solar still desalination
system with enhanced productivity, vol. 335 , pp. 27-32.
Charcosset, C. (2009). A review of membrane processes and renewable energies for
desalination, vol. 28 , pp. 214-245.
Esfahani, J.A., Rahbar, N., and Lavvaf, M. (2011). Utilization of thermoelectric
cooling in a portable active solar still-An experimental study on winter days, vol. 269,
pp. 198-205.
Elango, C.,Gunasekaran, N., and Sampathkamar, K. (2015). Thermal models of solar
still – a comprehensive review, vol. 47, pp. 856-911.
Eltawil, M. A. , Zhengming, Z. , and Yuan, L. (2008). Renewable energy powered
desalination system :- technologies and economic state of the art, vol. 12.
Ghali, K., Ghaddar, N., and Alsaidi, A. (2010). Optimized operation of an integrated
solar desalination and air-conditioning system: theoretical study, pp. 1-4.
Greenlee, L.F. , Lawler, D.F. , Freeman, B.D. , Marrot, B. , and Moulin, P.(2009).
Reverse osmosis desalination: water sources, technology, and today's challenges, vol.
43 , pp. 2317–2348.
Kabeel, A. E. , Omara, A. K. , and Younes, M.M. (2015). Techniques used to improve
the performance of the stepped solar still—A review, vol. 46 , pp. 178–188.
Kabeel, A.E. , Hamed,A. M. ,El Agouz, S.A. (2010). Cost analysis of different solar
still configuration , vol. 35, pp. 2901-2908.
Kalogirou, S. (2005). Seawater desalination using renewable energy sources, vol. 31,
pp. 242–281.
Kumar, P. V. , Kumar, A., Prakash, O., and Kaviti, A. K. (2015). Solar stills system
design: A review, vol. 51 , pp. 153–181.
Mezher, T. , Fath , H. , Abbas, Z. , and Khaled, A. (2011). Techno economic
assessment and environmental impacts of desalination technologies, vol. 73, pp. 263-
266.
Muftah, A. F., Alghoul, M. A. , Fudholi, A. , Abdul-Majeed, M. M. ,and Sopian, K.
(2014). Factors affecting basin type solar still productivity: A detailed review, vol. 32
, pp. 430–447.
56 Page MS.c Thesis- I. Abu Hassaneen
Murugavel, K. K. , Anburaj, P., Hanson, R.S. , and Elango, T. (2013) Progresses in
inclined type solar stills, vol. 20 , pp. 364–377.
Murugavel, K. , Manokar, M. and Muthu, E. (2014). Different parameters affecting
the rate of evaporation and condensation on passive solar still – A review , vol. 38, pp.
309–322.
Omara, Z. M., Kabeel, A. E., and Younes, M. M. (2014). Enhancing the stepped solar
still performance using internal and external reflectors, vol. 78 , pp. 876-881.
Penate, B., Garcia-Rodriguez , L. (2012). Current trends and future prospects in the
design of seawater reverse osmosis desalination technology, vol. 284, pp. 1–8 .
Qiblawey, H. M. and Banat, F. (2008). Solar thermal desalination technologies, vol.
220, pp.633–644.
Sangi, R. (2012). Performance evaluation of solar chimney power plants in Iran, vol.
16, pp. 704-710.
Sampathkumar, K. , Arjunan, T.V., Pitchandi, P. , and Senthilkumar, P. (2010) Active
solar still – A detailed review, vol. 14, pp.1503-1526.
Saxena, A., Varun and El-Sebaii, A.A. (2015). A thermodynamic review of solar air
heaters,” vol. 43 , pp. 863–890.
Sharon, H., and Reddy, K.S. (2015). A review of solar energy driven desalination
technologies, vol. 41, pp. 1080-1118.
Solar Tracker (2014). Available from: www.reuk.co.uk/Solar-Tracker.htm Accessed:
August 10, 2014.
Tanaka, H. (2010). Monthly optimum inclination of glass cover and external reflector
of a basin type solar still with internal and external reflector, vol. 84 , pp. 1959–1966.
Tanaka, H. , and Nakatake, Y. (2007). Effect of inclination of external flat plate
reflector of basin type still in winter, vol.81, pp. 1035-1042.
Torres, A. M. D. and Rodriguez, L. G. (2007). Status of solar thermal-driven reverse
osmosis desalination, vol. 51, pp. 216-242 . Velmurugana, V., and Sritharb, K . (2011). Performance analysis of solar stills based
on various factors affecting the productivity—A review, vol.15, pp. 1294–1304.
Velmurugana, V., and Sritharb, K. (2011). Performance analysis of solar stills based
on various factors affecting the productivity—A review,” vol. 15 , pp. 1294–1304.
Velmurugana, V., and Sritharb, K. (2007). Solar stills integrated with a mini solar
pond analytical simulation and experimental validation, vol. 216, pp. 232–241.
World Health Organization (WHO). (2008). Guidelines for Drinking-water Quality.
Third edition- Incorporating the first and second addenda, vol. 1, Geneva.
5. Page MS.c Thesis- I. Abu Hassaneen
Appendix Table A:1 Experimental results of Stepped solar still with water depth 5 cm without
any modification on 20/07/2015 Sheet No. 1 of Appendix A
Tw-Tg
out
(°C)
P com.
(ml/h) P (ml/h)
T gout
(°C)
T gi
(°C)
Tw
(°C)
Tb
(°C)
Ta
(°C)
Time
(h)
0 0 0 26 27 26 27 26 7
1 10 10 28 32 29 30 28 8
7 40 30 30 44 37 38 29 9
11 115 75 33 53 44 45 31 10
14 235 120 38 57 52 53 33 11
15 540 305 42 63 57 58 34 12
19 925 385 44 67 63 64 35 13
20 1445 520 46 67 66 67 35 14
18 1935 490 46 65 64 65 34 15
15 2335 400 42 60 57 58 33 16
13 2655 320 39 52 52 53 32 17
9 2855 200 38 48 47 48 31 18
9 2975 120 36 43 45 46 30 19
9 3060 85 34 38 43 44 30 20
58 Page MS.c Thesis- I. Abu Hassaneen
Table A:2 Experimental results of Stepped solar still with water depth 10 cm without
any modification on 23/07/2015 Sheet No. 2 of Appendix A
Tw-Tg
out
(°C)
P com.
(ml/h) P (ml/h)
Tg out
(°C)
Tg in
(°C)
Tw
(°C)
Tb
(°C)
Ta
(°C)
Time
(h)
0 0 0 27 28 27 28 27 7
0 10 10 29 31 29 30 28 8
6 30 20 30 34 36 37 29 9
9 95 65 33 39 42 43 31 10
9 195 100 39 43 48 49 32 11
13 475 280 40 48 53 54 33 12
16 775 300 42 53 58 59 34 13
17 1275 500 43 57 60 61 34 14
15 1725 450 43 52 58 59 33 15
12 2110 385 42 49 54 52 32 16
10 2415 305 39 48 49 50 31 17
9 2610 195 37 46 46 47 30 18
9 2710 100 35 43 44 45 30 19
8 2785 75 32 42 40 41 29 20
59 Page MS.c Thesis- I. Abu Hassaneen
Table A:3 Experimental results of Stepped solar still with water depth 2 cm
on 25/07/2015 Sheet No.3 of Appendix A
Tw-Tg
out
(°C)
P com.
(ml/h) P (ml/h)
Tg out
(°C)
Tg in
(°C)
Tw
(°C)
Tb
(°C)
Ta
(°C)
Time
(h)
0 0 0 27 28 27 28 26 7
1 15 15 29 32 30 31 28 8
8 55 40 31 37 39 40 29 9
12 135 80 35 44 47 48 31 10
13 275 140 41 51 54 55 33 11
15 605 330 45 55 60 61 34 12
19 1045 440 47 57 66 67 35 13
21 1640 595 48 59 69 70 35 14
19 2165 525 46 56 65 65 34 15
15 2575 410 43 52 58 58 32 16
11 2905 330 40 48 51 52 31 17
11 3125 220 38 46 49 50 31 18
9 3270 145 37 44 46 46 30 19
9 3355 85 34 41 43 44 30 20
66 Page MS.c Thesis- I. Abu Hassaneen
Table A:4 Experimental results of Conventional solar still with water depth 5 cm
on 20/07/2015 Sheet No.4 of Appendix A
Tw-Tg
out
(°C)
P com.
(ml/h) P (ml/h)
Tg out
(°C)
Tg in
(°C)
Tw
(°C)
Tb
(°C)
Ta
(°C)
Time
(h)
0 0 0 27 27 27 28 27 7
1 10 10 28 31 29 30 28 8
6 40 30 30 35 36 37 30 9
9 110 70 33 39 42 43 31 10
10 220 110 36 44 46 47 32 11
11 500 280 40 47 51 52 33 12
13 890 390 43 51 56 57 33 13
14 1390 500 45 53 59 60 34 14
14 1830 440 43 51 57 58 34 15
13 2200 370 40 47 53 54 33 16
12 2475 275 38 46 50 51 32 17
13 2660 185 35 45 48 49 31 18
12 2770 110 34 44 46 47 29 19
12 2835 65 32 43 44 45 29 20
63 Page MS.c Thesis- I. Abu Hassaneen
Table A:5 Experimental results of Stepped solar still with water depth 2 cm
With internal mirror on 29/07/2015 Sheet No.5 of Appendix
Tw-Tg
out
(°C)
P com.
(ml/h) P (ml/h)
Tg out
(°C)
Tg in
(°C)
Tw
(°C)
Tb
(°C)
Ta
(°C)
Time
(h)
1 0 0 27 28 28 29 27 7
3 20 20 28 33 31 32 28 8
9 60 40 30 39 39 40 29 9
15 145 85 34 46 49 50 31 10
17 315 170 39 53 56 57 32 11
19 690 375 43 56 62 63 33 12
22 1180 490 45 58 67 68 34 13
23 1800 620 47 59 70 71 35 14
23 2335 535 45 57 68 69 34 15
17 2755 420 43 53 60 61 32 16
12 3075 320 41 48 53 54 31 17
11 3300 225 38 47 49 50 31 18
10 3440 140 36 45 46 47 30 19
8 3535 95 34 43 42 43 29 20
62 Page MS.c Thesis- I. Abu Hassaneen
Table A:6 Experimental results of Stepped solar still with water depth 2 cm
With glass cover cooling on 02/08/2015 Sheet No.6 of Appendix
Tw-Tg
out
(°C)
P com.
(ml/h) P (ml/h)
Tg out
(°C)
Tg in
(°C)
Tw
(°C)
Tb
(°C)
Ta
(°C)
Time
(h)
1 0 0 25 27 26 27 26 7
3 10 10 26 28 29 30 27 8
7 30 20 27 30 34 35 28 9
11 85 55 27 32 38 39 30 10
13 195 110 27 32 40 41 31 11
15 405 210 28 32 43 44 32 12
18 645 240 28 33 46 47 34 13
19 925 280 29 33 48 49 34 14
19 1195 270 28 33 47 48 33 15
15 1415 220 28 33 43 44 33 16
14 1605 190 28 33 42 43 32 17
13 1745 140 27 32 40 41 32 18
12 1865 120 27 31 39 40 31 19
10 1945 80 26 30 36 37 30 20
61 Page MS.c Thesis- I. Abu Hassaneen
Table A:7 Experimental results of Stepped solar still with water depth 2 cm
With pre heating water on 05/08/2015 Sheet No.7 of Appendix
Tw-Tg
out
(°C)
P com.
(ml/h) P (ml/h)
Tg out
(°C)
Tg in
(°C)
Tw
(°C)
Tb
(°C)
Ta
(°C)
Time
(h)
14 0 0 29 38 43 44 26 7
11 120 120 38 45 49 50 28 8
9 325 205 45 51 54 55 29 9
9 635 310 50 56 59 60 29 10
11 1075 440 54 63 65 66 32 11
15 1570 495 58 68 73 74 33 12
17 2240 670 60 73 77 78 34 13
19 2980 740 62 77 81 82 35 14
24 3660 680 58 79 82 83 34 15
23 4220 560 55 75 78 79 32 16
22 4655 435 53 74 75 76 32 17
20 5000 345 51 70 71 72 31 18
18 5245 245 50 64 68 70 29 19
17 5425 180 49 62 66 67 29 20
64 Page MS.c Thesis- I. Abu Hassaneen
Table A:8 Experimental results of Stepped solar still with water depth 2 cm With
internal and external mirrors on 07/08/2015 Sheet No.8 of Appendix
Tw-Tg
out
(°C)
P com.
(ml/h) P (ml/h)
Tg out
(°C)
Tg in
(°C)
Tw
(°C)
Tb
(°C)
Ta
(°C)
Time
(h)
1 0 0 27 28 28 29 27 7
3 40 40 29 34 32 33 28 8
8 100 60 31 39 39 40 30 9
14 195 95 35 47 49 50 31 10
19 390 195 39 54 58 59 32 11
20 780 390 44 55 64 65 34 12
24 1300 520 46 56 70 71 35 13
24 1940 640 48 58 72 73 35 14
22 2520 580 46 57 68 69 34 15
19 3000 480 44 54 63 62 33 16
15 3370 370 43 51 58 59 32 17
10 3630 260 41 48 51 50 31 18
8 3785 155 39 47 47 48 31 19
8 3890 105 37 46 45 46 30 20
65 Page MS.c Thesis- I. Abu Hassaneen
Table A:9 Experimental results of Stepped solar still with water depth 2 cm With
Pre heating water and glass cover cooling on 09/08/2015 Sheet No.9 of Appendix
Tw-Tg
out
(°C)
P com.
(ml/h) P (ml/h)
Tg out
(°C)
Tg in
(°C)
Tw
(°C)
Tb
(°C)
Ta
(°C)
Time
(h)
13 0 0 28 38 41 42 27 7
17 180 180 31 45 48 49 29 8
21 465 285 35 51 56 57 29 9
23 900 435 37 56 60 61 31 10
29 1410 510 38 63 67 68 33 11
34 2000 590 40 68 74 75 34 12
35 2640 640 42 73 77 78 35 13
40 3350 710 42 77 82 83 35 14
42 4040 690 40 79 82 83 34 15
42 4690 650 38 75 80 81 33 16
40 5280 590 37 74 77 78 32 17
38 5790 510 36 70 74 75 31 18
36 6250 460 34 64 70 71 30 19
35 6670 420 32 62 67 68 30 20