exploitation of solar energy in the process of ... · solar distillation systems are a possible...

International Journal of Computation and Applied Sciences IJOCAAS, Volume 5, Issue 1, August 2018, ISSN: 2399-4509

653

Abstract— Humanity faces a major problem: the lack of

drinking water around the world that can affect the human

future. Solar distillation systems are a possible solution to this

problem as solar energy is currently used in the production

of clean water for laboratory applications, drinking, and for

agricultural purposes, depending on the size of the system. In

this study, some improvements are being made to increase the

productivity of the solar distillation. Two types of solar

distillers were constructed and tested. The first is a simple

traditional solar tub, which can produce 3L/ m2 D of distilled

water in summer. Type II is characterized by its design in a

graduated form and this design increases the surface area

exposed to the sun, causing an increase of 22% of distilled

water production.

Index Terms— Solar energy, distillation, salty water,

productivity.

I. INTRODUCTION

he limited availability of drinking water in many parts

of the world is an old problem, and till now many

regions of the world inhabitants are suffering from this

problem. Historically, humans have always tried to treat

salt and brackish water and convert it into potable water

that can be used in drinking and agriculture [1, 2]. While

global fresh water resources are shrinking, due to explosive

population growth rates, as well as significant

environmental pollution that is caused by human activities

for energy production and industry [3, 4]. Fresh water can

be defined as water containing dissolved salts less than

about 1000 milligrams per mg (mg/l) [5]. In principle, only

shallow distillation allows pure water to evaporate from

the basin and to be collected on the glass cover, leaving all

particulate pollutants in the distilled basin [6]. In general,

fresh water is water that contains trace amounts of soluble

salts, especially sodium chloride [7]. Natural sources of

fresh water are rain, lakes, streams, rivers, and

groundwater with salt content of less than 500 ppm [8].

Saltwater is water that is naturally present in the ocean or

sea and has a high salinity. Full-strength sea water contains

35 parts of salt, especially sodium chloride per 1,000 parts

of water, while salinity is equal to 35 (p.p.t) equal to 3.5%

[9]. Too much salinity in the water is detrimental to human

health. Salinity is considered as 500 mg/litre but the lower

the better it is, and up to 1000 mg/l of salinity is considered

the maximum human consumption in the long term [10].

Any value greater than 1,000 (mg/l) has long-term adverse

health effects [11].

The distillation and desalination of water is not a new

process but it is very old, as the old models are the fixed

types that consist of a tank with black ground and

transparent cover. It is not necessary to boil and distil

water, and distillation is one of the many processes

available to purify the water [12]. The freely available sun

rays can provide the thermal energy that can be used to

accomplish this process [13]. The benefit of solar radiation

requires the use of more space to collect solar energy. Solar

distillation systems can be large or small in size and are

designed to serve one family with a capacity of 3 to 15

litres of drinking water per day, or designed to produce

much more fresh water for the processing of a village or

small town [14].

Solar-powered distillation systems are affordable and

technologically low cost. Distilled solar is a simple device

to obtain distilled drinking water and solar energy is used

as fuel for this process [15]. These desalination units have

low installation cost and no fuel consumption. However,

solar distillates are characterized by two important factors:

reduced production capacity of distilled water, and the

need for large space to receive solar radiation [16]. Solar

distillers consist of a rectangular basin with shallow water

and a basin made of glass or reinforced plastic. The bottom

of the basin is painted black to increase the absorption of

solar radiation [17]. The distilled solar does not contain

moving parts or filters and does not require any type of fuel

[18]. The rising water vapour from the aquarium is

condensed on the surface of a composite glass lid at the top

of the aquarium and collects condensate water. Solar

distillates are characterized by other industrial distillation

systems that do not require any kind of energy, nor are

skilled operators, they can be manufactured locally and do

not require complex maintenance, and low cost to build

and operate [19, 20].

The performance of the solar distillator depends

on the availability of solar radiation. The amount of solar

energy in Iraq is about 2500 kW/m2. So, Iraq is well

qualified for solar distillation and can be a good solution

for the production of fresh water [21]. The solar distillate

can be placed on the roof of the building, in the garden, or

anywhere as long as it reaches sufficient amount of

sunlight [22].

Distilled water produced from the solar system is not

commercially successful, because solar distillers use

natural evaporation and condensation in a process similar

to that of rain water [23]. This allows the natural pH level

to produce excellent quality compared to steam distillation

[23]. Pollution in the distilled basin causes some errors in

the construction of the basin and there are several ways to

reduce pollution from the materials in the basin itself [24].

Sodium bicarbonate can be added to the aquarium for

several days to avoid most volatile substances [25].

Distillate parts must be manufactured from noble materials

Exploitation of solar energy in the process

of purification of the land surface water

Jaafar A. Kadhum

T


653

to prevent any bad or toxic effect on the water flowing

through, even in high temperature conditions that may

occur, so the relatively low-cost polyvinyl chloride plastic

pipe is preferred [26]. Vinyl chloride has been identified as

a carcinogen that can be harmful to workers in the

manufacturing of ponds, so we must be very careful about

the use of these substances in the drinking water system. It

is therefore recommended to build distillation plants still

water each of the heat-resistant glass materials [26, 27].

Solar distillers are a useful device for the production of

potable water and are important for industrial application,

hospitals and laboratories as well as for radiator and battery

maintenance [28, 29].

To study the water distillation still as a thermal system,

first the control volume must de applied as shown in Figure

(1), and then consider the energy and mass balances around

the system [30].

Fig. 1: Water distillation still as a thermal system

Energy inters the system are [32]:

a. Direct radiation of solar energy.

b. Ambient and surrounding reflecting radiation energy.

Energy leaves the system are [33]:

a. Heat transfer from still walls by convection.

b. Heat transfer to surrounding by radiation.

c. Radiation lost energy to surrounding by reflection.

d. Heat energy transfer to ground by conduction.

e. Energy lost by clean water outlet.

f. Energy lost with waste salty water.

Due to the several number and complexity of the heat and

mass transfer, included in the water still system it was seen

that modelling the whole water still distillation system was

too complex [34].

The sun energy is not constant with the time and, also due

to the change of the sun location and the existence of dust

and clouds, air pollution and etc, along the day. The

unsteady state conditions are existed in all parameter of the

water still distillation, so it is too difficult to get a

mathematical formula with the unsteady state condition.

So, depending on practical work will by better and more

satisfaction in evaluation to approach the optimum system

[35, 36].

Finally important notes must be considered during this

study as follow:

- The size of the still must with a standard size as 1 or 2

meter square.

- The quantity of brine water in basin must be kept at

minimum, because a lot of salty water in basin will absorb

the solar radiation energy and remain the salty water

temperature at low level.

- The salty water basin walls must be insulated, because

some heat energy will escape to ambient, that tend to

redaction in still performance.

- The temperature deference between glass upper surface of

collector and salty water, must kept maximum as possible, it

is the important parameter which defined the still

performance.

- The transparency of glass condenser cover must be of

high quality to reduce the absorption of solar radiation

which tends to heat the glass.

- The distance between surface of salty water and glass

lower surface must be kept at minimum as possible, to

shortage the vapour transfer distance.

- The glass collector thickness must be at minimum to

increase the heat transfer of the condensed vapor to the

surrounding.

- Water distillation still must be placed in open space, with

high wind speed, and under sun light for along period of

time.

- The incident angle of the solar light on glass collector

surface must be kept vertical to reduce the reflectivity of

the light on the glass surface.

- The upper surface of the glass collector must be kept

clean, because dust will absorb the light energy and tends

to increase the glass temperature, this will reduce amount

of condense water on hot dusty glass.

- The water distillation still system must be completely

closed, to prevent any escape of the vapour to the

surrounding, only small pipe for salty water inlet and small

pipe for clean water outlet.

The aim of this study is to evaluate the enhancement in the

productivity of a gradual basin solar distiller and

comparing it of a simple single slope solar distiller with

same collector area in two main seasons in Iraq, summer

and winter. Any improvement or increase in the production

of solar distillate is an added benefit to the distillation

process. So, the proposed distiller will undergo an

improvement to raise the efficiency of distillation to be

suitable for work in the atmosphere of Iraq.

II. EXPERIMENTAL SETUP

Two solar distillers were fabricated and tested, to evaluate

the best one of them and to determine to determine the

possibility of improving the proposed distillate production.

The first simplified type of glass was built as rectangular

box; the upper transparent surface is inclined with 12o. The

glass box was painted with black color to absorb the

sunlight radiation as shown in Fig. (2).

Dimension and technical details of the basin are:

o Basin cross section area 1 m2

o Basin length 1200 mm

o Basin width 834 mm

o Front height 100 mm

o Rear height 200 mm

o Salty water capacity 70 litre

o Angle of glass collector 12 degree

o Salty water maximum depth 70 mm


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o Constricted material, all from glass.

Fig. 2: Simple single slope rectangular glass basin

The second model of distillation system, that has been

constructed with technical specification as the Water

vapour can move from the hot part which facing the sun to

the cold part in opposite face of the system or we can say

in shadow face, and the collector bed covered by charcoal

to absorb the water and form the sun as shown in Fig. (3).

Fig. 3: Gradual solar distillation system with vapor circulation

technology

Dimension and Technical details as following:

o Collector length. 1200 mm

o Collector width. 834 mm

o Collector thickness. 120 mm

o Collector bed covered by charcoal.

o Make the bed as graduate surface to keep the

water in all side of the bad.

o Introduce sun-tracking system to keep the sun

radiation fall vertically along the day.

Experiments were conducted in Iraqi summer (June to

August 2017) and winter (mid November 2017 to end of

January 2018) to verify the Iraqi climates effects on both

distillers.

A. Tests Procedure

The two studied distillers were put on the roof of the

Energy and Renewable Energies Technology Center in the

University of Technology. The productivity of the two

stills was measured twice a week for the studied period

with conditions of shiny and no shadow from clouds or

dust. The basin water temperature was measured also as

well as the ambient temperature. The average of the

measured data (temperature and productivity) was taken

and compared.

III-RESULT AND DISCUSSION

Fig. 4 shows the temperature distribution for winter season

for the water in the distillers' basin and ambient

temperature. The graduate distiller raise the water

temperature in its basin compared to the simple single

slope solar distiller and ambient air. This increase in the

temperature comes from the increase in the basin area. This

increase in the basin area has increased the overall gained

temperature by 67.8%.

Fig. 4: The tested distillers' basin temperatures variation with

time at winter season

Fig. 5 shows that the two tested distillers' temperatures rose

highly at summer season compared to winter. The

maximum achieved temperature was 70°C for graduate distiller water. Here we must concentrate on the high

ambient temperature of Iraqi weathers at summer season

as the maximum average temperature recorded for the

testing period was 50°C. This high temperature inhibits the

cooling of the glass, reducing the heat transferred to the air,

and as a result negatively affected the distillation

productivity.

0

10

20

30

40

50

60

7 10 13 16 19

Tem

per

atu

re (°C

)

Time (hours)

Simple SD

Gradual SD

Ambeint temperature


653

Fig. 5: The tested distillers' basin temperatures variation with

time at summer season

Fig. 6 represents the average productivity of the two tested

distillers at winter season. In this season, the productivity

of the graduate distiller exceeded the simple single slope

solar distiller. This was because of the better heating of

basin water for the graduate distiller. The average increase

in productivity was 32.9%, which indicates that this

distiller is better than the simple distillate in winter season

of Iraq.

Fig. 6: The tested distillers' productivity variation with time at

winter season

Fig. 7 declares the average productivity of the tested stills

at summer season of Iraq. In the summer, the ambient

temperature is high and also solar radiation intensity is

high, which leads to higher water temperatures in the

distilled basin as shown in the figure 5. However, during

the period from 12 AM to 3 PM, the yield of the two

distillates is less than expected. The reason for this is the

high temperature of the condenser (distiller's glass) and

because of the high temperature of the external atmosphere

does not cool the glass to the desired level required, which

reduces the distillation productivity. This phenomenon has

been studied by Ref. [37] in detail and developed solutions.

The reader interested in this issue can return to the

reference above.

Fig. 7: The tested distillers' productivity variation with time at

summer season

VI- CONCLUSION

It seems that the use of small distillation stills is suitable

solution for supplying a family by fresh water. The first

and most important requirement for using solar distillation

is satisfied, which is the high solar energy. Radiation

density in Iraq is suitable for this application. The tests

were conducted on two fabricated distillers. The

performance of the two distillers declared that the single

slope solar distiller type is simple and cheap. It does not

require skilled workers to build it, low maintenance

required with low fresh water production, as the maximum

production of this type was about 3l/m2.D in average at

winter season. It is not small quantity, it is sufficient for

one person, especially if we know that it is cheap in price,

simple to maintain and easy to constructed. So a collection

of two or three units is sufficient to supply clean water for

drinking and cooking purposes of one small family. The

second distillation system is more complex but its

productivity is higher than the first still at winter. Its defect

is more complex in construction. It can produce about 4.5

L/m2 D. This distiller has low productivity as the first one

at summer due to difficulty of cooling the condenser

(glass).

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