solar pond - project (autosaved)

8/2/2019 Solar Pond - Project (Autosaved)

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CHAPTER 1

INTRODUCTION

1.1Solar Energy

Solar energy is radiant energy that is produced by the sun. Every day

the sun radiates, or sends out, an enormous amount of energy. The sun radiates

more energy in one second than people have used since the beginning of time!

Where does the energy come from that constantly radiates from the sun? It comes

from within the sun itself. Like other stars, the sun is a big ball of gasesmostly

hydrogen and helium atoms. The hydrogen atoms in the suns core combine to

form helium and generate energy in a process called nuclear fusion.

During nuclear fusion, the suns extremely high pressure and

temperature cause hydrogen atoms to come apart and their nuclei (the central cores

of the atoms) to fuse, or combine. Four hydrogen nuclei fuse to become one helium


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atom. But the helium atom contains less mass than the four hydrogen atoms that

fused. Some matter is lost during nuclear fusion. The lost matter is emitted into

space as radiant energy.

It takes millions of years for the energy in the suns core to make its

way to the solar surface, and then just a little over eight minutes to travel the 93

million miles to Earth. The solar energy travels to the Earth at a speed of 186,000

miles per second, the speed of light. Only a small portion of the energy radiated by

the sun into space strikes the Earth, one part in two billion. Yet this amount of

energy is enormous. Every day enough energy strikes the United States to supply

the nations energy needs for one and a half years!

Where does all this energy go? About 15 percent of the suns energy

that hits the Earth is reflected back into space. Another 30 percent is used to

evaporate water, which, lifted into the atmosphere, produces rainfall. Solar energy

is also absorbed by plants, the land, and the oceans. The rest could be used to

supply our energy needs.

1.2 Solar ponds

A solar pond collects and stores solar energy. Solar energy will warm

a body of water (that is exposed to the sun), but the water loses its heat unless

some method is used to trap it. Water warmed by the sun expands and rises as it

becomes less dense. Once it reaches the surface, the water loses its heat to the air

through convection, or evaporates, taking heat with it. The colder water, which isheavier, moves down to replace the warm water, creating a natural convective

circulation that mixes the water and dissipates the heat. The design of solar ponds

reduces either convection or evaporation in order to store the heat collected by the

pond. They can operate in almost any climate.


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SYNOPSIS

SUN is largest renewable energy source in the world .This energy is

collected and stored by various methods. But our case this energy is collected and

stored by another one important renewable energy of WATER. This method is

called SOLAR POND. Here the collecting medium is water and storage medium is

salt.

The collection of solar energy is different according to the sunshine.

And the storage level also different according to the salt content, density, pH value,

and concentration and heat loss.

This method should not affect the environment and cheapest method. In

this method two renewable energy are combine to produce power.

In this solar pond various types are available but we are chosen method

is Salinity-Gradient Solar Pond .We are doing to analyze the temperature level andstorage level. In analyze is carried out by various water. That is ordinary water

with salt, ground water and sea water.


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CHAPTER 2

TYPES OF SOLAR POND

2. Types of Solar Ponds

There are two main categories of solar ponds: nonconvecting ponds,

which reduce heat loss by preventing convection from occurring within the pond;

and convecting ponds, which reduce heat loss by hindering evaporation with a

cover over the surface of the pond.


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2.1 Convecting Pond

A well-researched example of a convecting pond is the shallow

solar pond. This pond consists of pure water enclosed in a large bag that allows

convection but hinders evaporation. The bag has a blackened bottom, has foam

insulation below, and two types of glazing (sheets of plastic or glass) on top. The

sun heats the water in the bag during the day. At night the hot water is pumped into

a large heat storage tank to minimize heat loss. Excessive heat loss when pumping


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the hot water to the storage tank has limited the development of shallow solar

ponds. Another type of convecting pond is the deep, saltless pond. This convecting

pond differs from shallow solar ponds only in that the water need not be pumped in

and out of storage. Double-glazing covers deep saltless ponds. At night, or when

solar energy is not available, placing insulation on top of the glazing reduces heat

loss.

2.2 Non-Convecting Ponds

There are two main types of non-convecting ponds: salt gradient

ponds and membrane ponds. A salt gradient pond has three distinct layers of brine(a mixture of salt and water) of varying concentrations. Because the density of the

brine increases with salt concentration, the most concentrated layer forms at the

bottom. The least concentrated layer is at the surface. The salts commonly used are

sodium chloride and magnesium chloride. A dark-colored material usually butyl

rubber lines the pond. The dark lining enhances absorption of the suns radiation

and prevents the salt from contaminating the surrounding soil and groundwater. As

sunlight enters the pond, the water and the lining absorb the solar radiation. As a

result, the water near the bottom of the pond becomes warm up to 200o F

(93.3oC). Although all of the layers store some heat, the bottom layer stores the

most. Even when it becomes warm, the bottom layer remains denser than the upper

layers, thus inhibiting convection. Pumping the brine through an external heat

exchanger or an evaporator removes the heat from this bottom layer. Another

method of heat removal is to extract heat with a heat transfer fluid as it is pumped

through a heat exchanger placed on the bottom of the pond. Another type of non

convecting pond, the membrane pond, inhibits convection by physically separating

the layers with thin transparent membranes. As with salt gradient ponds, heat is

removed from the bottom layer.


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2.2.1 Natural Solar Lakes

Naturally occurring salinity gradient solar lakes are known as

heliotherma lakes, the salinity gradient is the halocline, and the temperature

gradient is the thermolcline. These lakes are either a chloride or sulfate brine.

Saline lakes with a density gradient are referred to as meromictic and the density

gradient is called the pycnocline. Natural solar lakes have importance for solar

ponds because many of the early advances in the understanding of double-

diffusive convection were made by the scientists who were studying the natural

lakes and similar phenomena in the oceans. A good example of natural solar lake is

Lake Medve in Transylvania, then in Hungary (Hull, 1979).

2.2.2 Artificial Solar Ponds

The studies on artificial solar ponds were initiated in Israel in

1948 by Dr Rudolph Bloch and carried out by a group led by Tabor until 1966

(Boegli et al., 1982; Collins et al., 1985). The first artificial solar pond was built in

Israel in the beginning of 1958. Artificial solar ponds offer low cost heat and are

also known as man-made solar ponds. These solar ponds demonstrated

advancement of solar pond technology in Israel including electricity generation on

a relatively large scale. On the basis of convection, artificial solar ponds can be

classified into two groups known as convective and non-convective solar ponds.

2.2.3 Unsaturated Solar Ponds

The salt gradient solar pond also referred to as the unsaturated

solar pond is thermodynamically unstable. The concentration gradient decays

gradually, as the result of salt diffusion potential between the concentrated solution

at the bottom and the more dilute upper layers. This tendency towards the


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destruction of the layered configuration can be counteracted only by a proper

maintenance of the pond (Vitner., et al., 1990).

2.2.4 Saturated Solar Ponds

Another form of non-convective solar pond is a saturated solar

pond. It uses salts like KNO3, NH4NO3, and MgCl2, whose solubility increases

rapidly with temperature in the pond and saturation of salt concentration is

maintained at all depths. The pond is hottest at the bottom region and the

temperature progressively decreases from the bottom to the top. Consequently an

increasing concentration of salt is found towards the bottom. Because there is

saturation at each level, the vertical diffusion of salt is checked and the density

gradient is stable. This provides the possibility of a maintenance free solar pond.

Because of the solute cycle, saturated solar ponds have the possibility for self

maintenance. The diffusion from the concentrated bottom layer increases the

concentration in the upper layers. Then evaporation from the surface reinforced by

winds brings the upper layer to supper saturation, which is relieved under suitable

conditions by crystallization. The crystals, on attaining the proper size, sink to the

bottom and dissolve there, completing the solution cycle.

2.2.5 Gel Solar Pond

In gel or viscosity stabilized solar ponds, the non-convecting

layer is composed of a viscous polymer gel positioned by transparent films. The

gel is located in the upper part of the solar pond, is less dense than water and is

optically clear. It provides insulation against heat loss, and allows the sun to heat

the bulk of the water below the gel. The gel has low thermal conductivity and is


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viscous enough to avoid convection. It uses high viscosity rather than a salinity

gradient to suppress convection.

2.2.6 Salinity-Gradient Solar Pond

The Salinity or salt gradient solar pond is thermodynamically

unstable. The concentration gradient decays gradually as the result of the salt

diffusion potential between the concentrated solution at the bottom and the more

dilute upper layers. This tendency towards the destruction of the layered

configuration can be counteracted only by a proper maintenance of the pond.

CHAPTER 3

SALINITY-GRADIENT SOLAR POND

3.1 INTRODUCTION


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A salinity-gradient solar pond (SGSP) is a combined solar energy

collector and heat storage system reliant upon an aqueous solution of salt at

varying densities to suppress natural convection and store thermal energy. The

SGSP consists of three different zones; the upper convective zone (UCZ) with

uniform low salinity; a non-convective zone (NCZ) with a gradually increasing

density; and a lower convective zone (LCZ), called the storage zone.

Figure 3.1 Schematic of a salt gradient solar pond

A solar pond is a solar thermal collector and storage system which

is essentially a water pool with suppressed heat losses. It can supply heat up to a

temperature of approximately 95 c0 as shown in Figure 3.1. The Solar pond

involves simple technology and uses water as working material for collection of

solar radiant energy and its conversion to heat, storage of heat and transport of

thermal energy out of the system Solar pond technology inhibits heat loss

mechanisms by dissolving salt into the bottom layer of the pond, making it too

heavy to rise to the surface, even when hot.


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The salt concentration increases with depth, thereby forming a salinity

gradient. The solar energy which reaches the bottom of the pond remains entrapped

there. The useful thermal energy is then withdrawn from the solar pond in the form

of hot brine. The pre-requisites for 2 establishing solar ponds are: a large tract of

land, solar radiation, and cheaply available salt such as Sodium Chloride or bittern.

A salt gradient solar pond is an efficient, low cost solar energy collection

and long range storage system for low temperature heat. In a salinity gradient solar

pond, the concentration of salt dissolved in the water increases with depth. It is

important to maintain the clarity of a solar pond to allow as much solar radiation as

possible to reach the lower zone. The stability of its salinity gradient must also be

maintained for it to perform efficiently as a store of solar energy. Water clarity is

essential for high performance of solar ponds.

3.2 History

Naturally occurring solar ponds are found in many places on the earth (

Hull et al.,1988).Solar energy was first used approximately 2500 years ago when

great Roman baths were heated by the sun (Arumugam, 1997). The discovery of

solar ponds dates back to the early years of 1900s. The phenomenon of natural

solar ponds was first discovered by Von Kalecsinky in natural occurring lakes in a

salt region of Transylvania and Hungry (Hull et al, 1989 citing V. Kalecsinsky,

1902). One of the natural solar lakes was found near Elat, Israel. This lake wasmixed and salinity uniformly high during summer but, during the winter, the fresh

seawater forms a relatively low saline upper layer, giving rise to the solar pond

effect. Naturally occurring salinity gradient or solar lakes were found in many

places in Israel and Hungry.


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Following the natural solar lakes concept, further investigations were

conducted in the 1950s and 1960s in Israel in relation to artificial solar ponds. The

cumulative research experience provided some insight into how future solar pond

facilities can be designed and operated to extract solar heat. Artificial solar ponds

offer the promise of low cost heat. However, to the present day, most man-made

solar ponds have been constructed and operated primarily as research and

development facilities.

The first artificial salinity gradient solar pond was established at Sdom,

Israel in 1960. The pond was of size 25 x 25 m and 0.8 m depth. The purpose of

this pond was to study the physics of the solar pond and its economic viability. The

pond operated between September 1959 and April 1960 and attained a maximum

heat storage zone temperature of 92o C. The second solar pond at Sdom was

operated between June and December 1962.

In addition to the Sdom solar pond in Israel, two more experimental solar

ponds were constructed. One of these ponds was very close to the first pond

located at Sdom while the second pond was contructed at Atlith Salt works near

Haifa, Israel (Tabor, H., et al 1965). The solar pond constructed at En Boqeq in

Israel was started in 1979 and it was the first solar pond to generate and supply

commercial electricity at a peak output of 150KW.Another solar pond was built in

1984 at Bet Ha Arava in Israel and this solar pond supplies a 5 MW power station.

Solar pond technology was introduced in the United States in 1973 with the

work of Rabl and Nielson at Ohio State University and the experimental work was

mostly related to heat extraction. The solar pond constructed at Chattanooga,

Tennessee, together with two auxiliary ponds, was used for brine control and heat


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extraction until 1986. In Iowa, New Jersey, Ohio and EI Paso, Texas, commercial

solar ponds are being used for heat extraction for private use.

In Australia, Solar ponds were initially investigated in a research project

undertaken between 1964 and 1966 (Tabor, H.Z., 1966). The research work on

solar ponds was begun again in Australia in 1979. Solar ponds in Australia were

constructed for research and development but some of these solar ponds have also

generated commercial electricity including a solar pond at Pyramid Hill, Victoria.

A solar pond was built in 1984 at Alice Springs, Northern Territory.

In Melbourne, the University of Melbourne in conjunction with Cheetham

Salt Ltd is operating two solar ponds at salt works for research purposes. The

Energy Conservation and Renewable Energy group at RMIT University, Bundoora

East has initiated a research & development project in conjunction with Pyramid

Salt Pty Ltd at Pyramid Hill in northern Victoria. The solar pond at Pyramid Hill

was officially opened on 14 August 2001 and began supplying heat for commercial

salt production in June 2001. Geo-Eng Australia and Pyramid Salt, in conjunction

with RMIT University, were working together on this project. The current research

indicates that there is little evidence of publication in the field of clarity

monitoring, maintenance and stability control of solar pond operation (Tsilingiris,

Panayopas, T; 1988, 41-48). Several different clarification techniques have been

used in the past including acidification, polymerization, filtration and saturation,

but all these techniques were found to have some disadvantages, such as chemical

handling and corrosion of diffusers and pipes.

In another study, the spectral transmission of halo bacteria and selected

chemicals in de-ionized water at several concentrations levels were determined for

their effect on solar radiation transmission in salt water (Wang, J; et al., 1993). The


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chemicals that were used included copper sulphate, hydrochloride acid and bleach.

However, there is still little 16 literature on the effects of water turbidity and salt

concentration levels on solar penetration (Kishore, V.V.N; et al, 1996).

In another study, a major problem with bittern and seawater solar ponds has

been found to be the growth of algae and bacteria for example in the Margherita Di

Savoia solar pond project (Folchitto, S, 1993). In another investigation, three

significant aspects of solar pond operation using bittern were discussed including

monitoring of thermal and salinity profile data, reduction of wind and filtration

techniques for water clarity (Macdonald, R.W.G.; et al., 1991).

Most of the previous research work on maintaining clarity in solar ponds

was carried out using chemical techniques. These techniques are expensive and

have disadvantages like hazards in chemical handling and potential corrosion of

metal components including diffusers and pipes for heat extraction and brine

transfer (Lu, Huanmian, et al., 1993). Brine shrimps have been used previously in

biological management of solar salt works (Tackaert, W; et al., 1993). However,

study indicates that the use of brine shrimps to maintain water clarity in bittern

solar ponds has not been investigated before. Generally, there have been few

investigations of the methods for the removal of algae and bacteria in bittern

ponds.

In this study, brine shrimps were used in salinity gradient solar ponds to

achieve good water clarity and thermal efficiency. As a result of successful

application of a biological method (brine shrimps), good brine transparency in a

solar pond has been achieved and water clarity was improved. Research work also

established that the biological method is economical and cost effective. The main

objective of this research project was to investigate chemical and biological


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techniques for maintaining solar pond water clarity and salinity gradient, and hence

maximize the thermal efficiency. Solar ponds constructed both using common salt

(sodium chloride) and bittern (a waste-product of common salt production

comprising mainly magnesium chloride) are studied. This research has

demonstrated that solar pond technology is economical and feasible for storing

significant amounts of energy for several days. The solar pond approach is now

adopted in almost all parts of the world and interest in the technology continues to

increase. A number of projects in numerous countries are 17 being undertaken, and

these activities indicate the interest in using solar pond technology for a wide

variety of purposes.

3.3 ZONES

The SGSP consists of three different zones; the upper convective zone

(UCZ) with uniform low salinity; a non-convective zone (NCZ) with a gradually

increasing density; and a lower convective zone (LCZ), called the storage zone.

Fig: 3.2 zones of solar pond


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3.3.1 The Upper Convective Zone

An upper convective zone consists of clear fresh water whichacts as a solar collector or receiver and has relatively small depth and is generally

close to ambient temperature. The upper convective zone is the primary site where

external environmental influences impinge upon the pond. The upper convective

zone is influenced by wind agitation and convective mixing. Its thickness is

between 0.2-0.5 m and its salinity ranges from 2% to 80%. The upper convective

zone is a zone of absorption and transmission.

3.3.2 The Non-Convective Zone

The non-convective zone has a salt gradient, is much

thicker than the upper convective zone and occupies more than half the depth of

the pond. Salt concentration and temperature increase with depth. The non-

convective zone separates the upper and lower convective zones and that possess

several different salt concentration layers, constituting a salinity gradient. The

main focus of concern for the gradient zone is on its internal stability. A solar pond

cannot operate without an internally stable salinity gradient and, as part of a

minimum requirement; density must either be uniform or increase downwards to

prevent any gravitational overturn. This means that the salt concentration must

increase downwards as well. Instability of a solar pond is usually linked to a weak

salt gradient, commonly because of a gradient breakdown. Due to its unique

makeup, the gradient zone acts primarily as insulation so that little energy is lost

when solar radiation is transmitted through the surface zone and the gradient zone

and stored in the lower convective zone.

3.3.3 The Lower Convective Zone


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The lower convective zone has high salt concentration and

serves as the heat storage 3zone. Almost as thick as the middle non-convective

zone, salt concentration and temperatures are nearly constant in this zone. The

lower convective zone is normally the region in which useful heat is stored and

from which it is extracted. Most of the heat removed derives from heat provided by

solar energy either absorbed in the volume of pond water or the floor of the pond.

There may also be heat transfer to or from the gradient zone and heat transfer to or

from the earth underneath the lower zone and the floor of the pond. Heat removal

can be accomplished by extracting brine or usually by passing it through an

external heat exchanger. The lower convective zone is a homogeneous,

concentrated salt solution that can be either convecting or temperature stratified.

Above it the non-convective gradient zone constitutes a thermal insulation layer

that contains a salinity gradient. Unlike the surface zone, transparency in the lower

convective zone does not have as much influence on the thermal performance of

the solar pond, poor transparency resulting mostly from dirt from the bottom of the

pond stirred up by circulation in the lower region. The simplicity of the solar pond

and its capability of generating sustainable heat above 60 0 C makes it attractive for

a lot of applications. The energy stored and collected in a solar pond is low grade

heat at temperatures limited by the boiling point of the bottom zone brine.


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CHAPTER 4

TEMERATURE MEASUREMENT

4. 1 Temperature Measurement

Temperature can be measured via a diverse array of sensors.

All of them infer temperature by sensing some change in a physical characteristic.

Six types with which the engineer is likely to come into contact are:

1. Thermocouples

2. Resistive Temperature Devices (RTDs and thermistors)3. Infrared Radiators


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4. Bimetallic Devices5. Liquid Expansion Devices6. Change-Of-State Devices

4.1.1 Thermocouple Temperature Measurement

Sensors

Thermocouples consist essentially of two

strips or wires made of different metals and joined at

one end. Changes in the temperature at that juncture

induce a change in electromotive force (emf) between

the other ends. As temperature goes up, this output

emf of the thermocouple rises, though not necessarily

linearly.

4.1.2 Resistance Temperature Devices (RTD)

Resistive temperature devices capitalize on

the fact that the electrical resistance of a material

changes as its temperature changes. Two key types are

the metallic devices (commonly referred to as RTDs),

and thermistors. As their name indicates, RTDs rely on

resistance change in a metal, with the resistance rising

more or less linearly with temperature. Thermistors are

based on resistance change in a ceramic

semiconductor; the resistance drops nonlinearly with

temperature rise.
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4.1.3 Infrared Temperature Measurement Devices

Infrared sensors are non-contacting devices.

They infer temperature by measuring the thermalradiation emitted by a material.

4.1.4 Bimetallic Temperature Measurement

Devices

Bimetallic devices take advantage of the

difference in rate of thermal expansion between

different metals. Strips of two metals are bonded

together. When heated, one side will expand more than

the other, and the resulting bending is translated into a

temperature reading by mechanical linkage to a

pointer. These devices are portable and they do not

require a power supply, but they are usually not as

accurate as thermocouples or RTDs and they do not

readily lend themselves to temperature recording.

4.1.5 Fluid-Expansion Temperature Measurement

Devices

Fluid-expansion devices, typified by the

household thermometer, generally come in two main

classifications: the mercury type and the organic-liquid

type. Versions employing gas instead of liquid are also

available. Mercury is considered an environmental

hazard, so there are regulations governing the
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shipment of devices that contain it. Fluid-expansion

sensors do not require electric power, do not pose

explosion hazards, and are stable even after repeated

cycling. On the other hand, they do not generate data

that is easily recorded or transmitted, and they cannot

make spot or point measurements.

4.1.6 Change-of-State Temperature Measurement

Devices

Change-of-state temperature sensors consist

of labels, pellets, crayons, lacquers or liquid crystals

whose appearance changes once a certain temperature

is reached. They are used, for instance, with steam

traps - when a trap exceeds a certain temperature, a

white dot on a sensor label attached to the trap will

turn black. Response time typically takes minutes, so

these devices often do not respond to transienttemperature changes. And accuracy is lower than with

other types of sensors. Furthermore, the change in

state is irreversible, except in the case of liquid-crystal

displays. Even so, change-of-state sensors can be

handy when one needs confirmation that the

temperature of a piece of equipment or a material has

not exceeded a certain level, for instance for technical

or legal reasons during product shipment.
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4.2 Types of Thermocouple

Certain combinations of alloys have become popular as industry

standards. Selection of the combination is driven by cost, availability, convenience,

melting point, chemical properties, stability, and output. Different types are best

suited for different applications. They are usually selected based on the

temperature range and sensitivity needed. Thermocouples with low sensitivities (B,

R, and S types) have correspondingly lower resolutions. Other selection criteria

include the inertness of the thermocouple material, and whether it is magnetic or

not. Standard thermocouple types are listed below with the positive electrode first,

followed by the negative electrode. They are

1. K

2. E

3. J

4. N

5. Platinum types B,R and S

5.1

B

5.2R

5.3S

6. T

7. C

8. M

9.

Chromel-gold/iron
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4.2.1 K

Type K (chromel{90 percent nickel and 10 percent chromium}

alumel)(Alumel consisting of 95% nickel, 2% manganese, 2% aluminium and 1%

silicon) is the most common general purpose thermocouple with a sensitivity of

approximately 41 V/C, chromel positive relative to alumel. It is inexpensive, and

a wide variety of probes are available in its 200 C to +1350 C / -328 F to

+2462 F range. Type K was specified at a time when metallurgy was less

advanced than it is today, and consequently characteristics may vary considerably

between samples. One of the constituent metals, nickel, is magnetic; a

characteristic of thermocouples made with magnetic material is that they undergo a

deviation in output when the material reaches its Curie point; this occurs for type K

thermocouples at around 350 C .

4.2.2 E

Type E (chromelconstantan)has a high output (68 V/C) which makes

it well suited to cryogenic use. Additionally, it is non-magnetic.

4.2.3 J

Type J (ironconstantan) has a more restricted range than type K (40 to

+750 C), but higher sensitivity of about 55 V/C. The Curie point of the iron

(770 C)causes an abrupt change in the characteristic, which determines the upper

temperature limit.

4.2.4 N

Type N (NicrosilNisil) (Nickel-Chromium-Silicon/Nickel-Silicon)

thermocouples are suitable for use at high temperatures, exceeding 1200 C, due to

their stability and ability to resist high temperature oxidation. Sensitivity is about
http://en.wikipedia.org/wiki/Chromelhttp://en.wikipedia.org/wiki/Alumelhttp://en.wikipedia.org/wiki/Metallurgyhttp://en.wikipedia.org/wiki/Nickelhttp://en.wikipedia.org/wiki/Curie_temperaturehttp://en.wikipedia.org/wiki/Chromelhttp://en.wikipedia.org/wiki/Constantanhttp://en.wikipedia.org/wiki/Cryogenichttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Constantanhttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Nicrosilhttp://en.wikipedia.org/wiki/Nisilhttp://en.wikipedia.org/wiki/Oxidationhttp://en.wikipedia.org/wiki/Oxidationhttp://en.wikipedia.org/wiki/Nisilhttp://en.wikipedia.org/wiki/Nicrosilhttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Constantanhttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Cryogenichttp://en.wikipedia.org/wiki/Constantanhttp://en.wikipedia.org/wiki/Chromelhttp://en.wikipedia.org/wiki/Curie_temperaturehttp://en.wikipedia.org/wiki/Nickelhttp://en.wikipedia.org/wiki/Metallurgyhttp://en.wikipedia.org/wiki/Alumelhttp://en.wikipedia.org/wiki/Chromel


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39 V/C at 900 C, slightly lower than type K. Designed to be an improved type

K due to increased stability at higher temperatures, it is becoming more popular,

though the differences may or may not be substantial enough to warrant a change.

4.2.5 Platinum types B,R and S

Types B, R, and S thermocouples use platinum or a platinum

rhodium alloy for each conductor. These are among the most stable thermocouples,

but have lower sensitivity than other types, approximately 10 V/C. Type B, R,

and S thermocouples are usually used only for high temperature measurements due

to their high cost and low sensitivity.

4.2.5.1 B

Type B thermocouples use a platinumrhodium alloy for each

conductor. One conductor contains 30% rhodium while the other conductor

contains 6% rhodium. These thermocouples are suited for use at up to 1800 C.

Type B thermocouples produce the same output at 0 C and 42 C, limiting their

use below about 50 C.

4.2.5.2 R

Type R thermocouples use a platinumrhodium alloy containing 13%

rhodium for one conductor and pure platinum for the other conductor. Type R

thermocouples are used up to 1600 C.

4.2.5.3 S

Type S thermocouples are constructed using one wire of 90%

Platinum and 10% Rhodium (the positive or "+" wire) and a second wire of

100% platinum (the negative or "-" wire). Like type R, type S thermocouples
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are used up to 1600 C. In particular, type S is used as the standard of

calibration for the melting point ofgold (1064.43 C).

4.2.6 T

Type T (copperconstantan) thermocouples are suited for measurements in

the 200 to 350 C range. Often used as a differential measurement since only

copper wire touches the probes. Since both conductors are non-magnetic, there is

no Curie point and thus no abrupt change in characteristics. Type T thermocouples

have a sensitivity of about 43 V/C.

4.2.7 C

Type C (tungsten 5% rhenium tungsten 26% rhenium) thermocouples are

suited for measurements in the 0 C to 2320 C range. This thermocouple is well-

suited for vacuum furnaces at extremely high temperatures. It must never be used

in the presence ofoxygen at temperatures above 260 C.

4.2.8 M

Type M thermocouples use a nickel alloy for each wire. The positive wire (20

Alloy) contains 18% molybdenum while the negative wire (19 Alloy) contains

0.8% cobalt. These thermocouples are used in vacuum furnaces for the same

reasons as with type C. Upper temperature is limited to 1400 C. It is less

commonly used than other types.

4.2.9 Chromel-gold/iron

In chromel-gold/iron thermocouples, the positive wire is chromel and the

negative wire is gold with a small fraction (0.030.15 atom percent) of iron. It can

be used for cryogenic applications (1.2300 K and even up to 600 K). Both the

sensitivity and the temperature range depends on the iron concentration. The
http://en.wikipedia.org/wiki/Goldhttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Constantanhttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Tungstenhttp://en.wikipedia.org/wiki/Rheniumhttp://en.wikipedia.org/wiki/Vacuum_furnacehttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Nickelhttp://en.wikipedia.org/wiki/Molybdenumhttp://en.wikipedia.org/wiki/Cobalthttp://en.wikipedia.org/wiki/Chromelhttp://en.wikipedia.org/wiki/Goldhttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Cryogenicshttp://en.wikipedia.org/wiki/Cryogenicshttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Goldhttp://en.wikipedia.org/wiki/Chromelhttp://en.wikipedia.org/wiki/Cobalthttp://en.wikipedia.org/wiki/Molybdenumhttp://en.wikipedia.org/wiki/Nickelhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Vacuum_furnacehttp://en.wikipedia.org/wiki/Rheniumhttp://en.wikipedia.org/wiki/Tungstenhttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Constantanhttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Gold


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sensitivity is typically around 15 V/K at low temperatures and the lowest usable

temperature varies between 1.2 and 4.2 K.

4.3 Multichannel Temperature Digital Controller

Multi-channel digital temperature indicator is an ideal instrument

virtually for any industry or application, where multi-channel temperature have to

be measured and monitored from a convenient and centralized place. This compact

and highly reliable instrument can accept any one type of RTD or thermocouple

sensors. All thermocouple inputs are compensated for cold junction error. The

scanned channel number is indicated on a 2-digit display and the scanned

temperature is indicated on a 31/2 digit display.

Fig 4.1 Multichannel Digital Controller

Open sensor indication is a standard feature. The temperature

indication resolution is 10c. This instrument can be used either in auto-scan or

manual mode. In manual mode the measured temperature can be viewed one

channel after another by pressing the Advance switch. In Auto scan mode, all

the channel are scanned and displayed automatically one channel after and if the

user desires to view any particular channel for a long time, by pressing the

HOLD.


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CHAPTER 5

SALT

5.1 Introduction

Salt, also known as table salt, or rock salt, is a mineral that is

composed primarily ofsodium chloride (NaCl), a chemical compound belonging to

the larger class ofionic salts. It is essential for animal life in small quantities, but is

harmful to animals and plants in excess. Salt is one of the oldest, most ubiquitous

food seasonings and salting is an important method offood preservation.

The taste of salt (saltiness) is one of the basic human tastes.

Salt for human consumption is produced in different forms: unrefined

salt (such as sea salt), refined salt (table salt), and iodized salt. It is a crystalline

solid, white, pale pink or light gray in color, normally obtained from sea water or

rock deposits. Edible rock salts may be slightly grayish in color because of mineral

content.

Chloride and sodium ions, the two major components of salt, areneeded by all known living creatures in small quantities. Salt is involved in

regulating the water content (fluid balance) of the body. The sodium ion itself is

used for electrical signaling in the nervous system. Because of its importance to

survival, salt has often been considered a valuable commodity during human

history. However, as salt consumption has increased during modern times,

scientists have become aware of the health risks associated with too much salt

intake, including high blood pressure. Therefore health authorities have

recommended limitations of dietary sodium. The United States Department of

Health and Human Services recommends that individuals consume no more than

15002300 mg of sodium (37505750 mg of salt) per day depending on age.
http://en.wikipedia.org/wiki/Rock_salthttp://en.wikipedia.org/wiki/Mineralhttp://en.wikipedia.org/wiki/Sodium_chloridehttp://en.wikipedia.org/wiki/NaClhttp://en.wikipedia.org/wiki/Salt_(chemistry)http://en.wikipedia.org/wiki/Animalhttp://en.wikipedia.org/wiki/Salting_(food)http://en.wikipedia.org/wiki/Food_preservationhttp://en.wikipedia.org/wiki/Tastehttp://en.wikipedia.org/wiki/Basic_tasteshttp://en.wikipedia.org/wiki/Sea_salthttp://en.wikipedia.org/wiki/Iodized_salthttp://en.wikipedia.org/wiki/Sea_waterhttp://en.wikipedia.org/wiki/Chloridehttp://en.wikipedia.org/wiki/Sodiumhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Fluid_balancehttp://en.wikipedia.org/wiki/Hypertensionhttp://en.wikipedia.org/wiki/United_States_Department_of_Health_and_Human_Serviceshttp://en.wikipedia.org/wiki/United_States_Department_of_Health_and_Human_Serviceshttp://en.wikipedia.org/wiki/United_States_Department_of_Health_and_Human_Serviceshttp://en.wikipedia.org/wiki/United_States_Department_of_Health_and_Human_Serviceshttp://en.wikipedia.org/wiki/Hypertensionhttp://en.wikipedia.org/wiki/Fluid_balancehttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Sodiumhttp://en.wikipedia.org/wiki/Chloridehttp://en.wikipedia.org/wiki/Sea_waterhttp://en.wikipedia.org/wiki/Iodized_salthttp://en.wikipedia.org/wiki/Sea_salthttp://en.wikipedia.org/wiki/Basic_tasteshttp://en.wikipedia.org/wiki/Tastehttp://en.wikipedia.org/wiki/Food_preservationhttp://en.wikipedia.org/wiki/Salting_(food)http://en.wikipedia.org/wiki/Animalhttp://en.wikipedia.org/wiki/Salt_(chemistry)http://en.wikipedia.org/wiki/NaClhttp://en.wikipedia.org/wiki/Sodium_chloridehttp://en.wikipedia.org/wiki/Mineralhttp://en.wikipedia.org/wiki/Rock_salt


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5.2 Salt Resources

The cost of salt is approximately 30 to 50 % of the total pond cost;

hence the solar pond should preferably be built near a salt producing area. The

coastal areas are economically advantageous zones as the sea is the natural source

of water and salt at very little cost. Also there is considerable advantage in locating

ponds in areas presently accepted as high salt regions. The basic criteria for salt

selection are transparency to solar radiation, low cost, minimal environmental

hazard, and adequate solubility.

5.3 Candidate Salts in solar pond

The essential components of a salinity gradient solar pond are

dissolved salt and water. To establish a salinity gradient requires only very

concentrated brine and a low- salinity brine or fresh water. The availability of low

cost brine or salts having suitable chemical and physical properties strongly affects

the overall economics of solar ponds.

The basic criteria for salt and brine selection are

Adequate solubility

Transparency to solar radiation.

Low cost

Minimal Environmental Hazard


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The solubility of the salt composition in water is of fundamental importance

because it determines the range of salinity (or salt concentration) and salinity

gradient profiles. Salt diffusivity and brine viscosity certainly influence gradient

stability and gradientboundary behavior.

Sodium chloride (NaCl) and magnesiun chloride (MgCl2) are the major

constituents of salts used in solar ponds. Sodium chloride (NaCl) brines have been

by far the most widely used salt solutions in solar ponds built around the world.

While there are many possible candidate salts, experience to date has been limited,

again with a few exceptions, to brine in which NaCl and or MgCl2 are the major

constituent salts. This can be correlated with the availability and cost.

The use of sodium chloride salt and water to produce solar pond brines has

the significant advantage of producing highly transparent solutions. During the

initial establishment of solar ponds, it has been demonstrated that the use of

sodium chloride and water provides a high degree of clarity because clean salt and

water produce clear brines in the ponds.

After sodium chloride (NaCl), magnesium chloride (MgCl2) is the second

largest salt constituent of sea water. Magnesium chloride (MgCl2) is a major

residue salt in the end brines of solar salt works. Compared to sodium chloride

(NaCl), magnesium chloride (MgCl2) provides much more concentrated brines and

greater density can be produced by dissolution of magnesium chloride (MgCl2)

salt in the water. As a practical result, solar ponds operated with magnesium

chloride (MgCl2) brines exhibit greater operational stability. It is established that

magnesium chloride (MgCl2) is more expensive than sodium chloride (NaCl) but

that in the salt processing plants, magnesium chloride (MgCl2) brine

concentrations are often cheaper. Bittern is concentrated seawater, a waste product


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in the manufacture of sodium chloride. It has sodium chloride (NaCl) and

magnesium chloride (MgCl2) as its main constituents. A chemical analysis of the

bittern used at the Laverton solar pond indicates the following major constituents

in mg/kg.

Table 5.1A Typical Bittern Chemical Composition (concentration mg/kg)

Chloride Sodium Magnesium Potassium Sulfate

180,000 51,000 36,000 12,000 6,000

5.3.1 Sodium Chloride

Sodium chloride has been used in many solar ponds around the

world because of its wide availability, relatively low cost and well known

properties. It is the major constituent of sea water and many other saline waters.

Sodium chloride based solar ponds are essentially an established technology for

low temperature applications. High- temperature applications of NaCl ponds

have also been successful but these applications require more careful operation and

maintenance procedures. Several ponds have operated at temperatures in excess of

80 0 C. The thermo physical properties of pure NaCl solutions have been widely

investigated.

5.3.2 Magnesium Chloride

Magnesium chloride (MgCl2), is the second largest constituent of

ocean water and it is also the principal evaporate of Dead Sea brine. Magnesium

chloride is a major residue salt in the end brines of solar salt works. Brines with

substantial MgCl2 concentration are often cheap and at a few selected sites they


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are freely available for the cost of pumping. Two experimental solar ponds in

Israel utilized MgCl2, as the only constituent salt. One of the largest solar ponds of

36,000 m 2 in the U.S uses magnesium brine. This pond uses a thin gradient zone

to keep the winter temperature of a deep brine storage pond above 130

C.

An experimental 850 m 2 pond using mixed MgCl2 and NaCl was operated at the

Great Salt Lake and magnesium ions are present in the brine used in the Los Banos

ponds. The Margherita di Savoia Solar, Pond 25,000 m 2 , 4 m deep, has been filled

with salt- work bittern and the gradient has been generated using seawater.


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CHAPTER 6

DESGIN AND CONSTRUCTION OF SOLAR POND

In this solar pond system having a number of components they are

1. Cylindrical tray

2. Glass plate(soda lime)

3. Insulation material

4. Thermocouple

5. Temperature digital controller

6.

Absorber medium (black coating, Nylon clothe)

7. Collecting & storage medium (Water and salt)


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1. Cylindrical Tray:It is made up of stainless steel sheet. The sizes of the sheet are

10075 cm and thickness is 5mm.the require size of the tray is 900580mm from

this required dimension the cylindrical shape is formed by the sheet metal

operation. Then the both end of the cylindrical sides are closed and its weld by the

Arc welding now the cylindrical tray is formed. The density and thermal

conductivity of the stainless steel are 7900kg/m3

and 15.1W/m K.

2.

Glass plate:The glass covers the top surface of the cylindrical tray box with

airtight. The glass dimension is 10075cm and thickness is 8mm.The transitivity

of ordinary glass is quite higher compared with other material and also hindrance

the Heat loss and evaporation. In this system three holes are drilled on the glass


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plates with equal diameter of 6mm. The first hole is drilled at the center of the

glass plate and another two holes are drilled on the left and right side from the

center hole with equal distance of 10cm. Then plastic tubes are inserted in three

holes with different height. The density and thermal conductivity of glass plate are

2500 kg/m3

and 7.44 W/m K.

3. Insulation material:Here, the thermocole is the insulation material. This material is

coated on the outside of cylindrical tray. It is used for minimize the heat

loss. The density and thermal conductivity are 1050kg/m3

and 0.036W/m K.


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ABSTRACT

A Solar pond may be used as a large area collection and forthe storage of solar energy. The salt gradient solar pond is a body saline is which

the concentration increases with depth. The density gradient inhibits thermal

convection with the result that solar radiation reaching the lower regions is trapped

and the temperature is raised. A method to estimate the storage temperature

radiation in the pond is described raise in .The storage temperature is estimated by

a numerical analysis using metrological observation data with a time interval of

one hour.


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WORKING PRINCIPLE:

The solar pond works on a very simple principle. It is well-known that water or air is heated they become lighter and rise upward. Similarly,

in an ordinary pond, the suns rays heat the water and the heated water from within

the pond rises and reaches the top but loses the heat into the atmosphere. The net

result is that the pond water remains at the atmospheric temperature. The solar

pond restricts this tendency by dissolving salt in the bottom layer of the pond

making it too heavy to rise.

A solar pond is an artificially constructed water pond in which

significant temperature rises are caused in the lower regions by preventing the

occurrence of convection currents. The more specific terms salt-gradient solar


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pond or non-convecting solar pond are also used. The solar pond, which is actually

a large area solar collector is a simple technology that uses water- a pond between

one to deep as a working material for three main functions.But in our sample

analyse project is small size solar pond is taken, small amount salt is used.

The some amount of salt is proceed in the pond it dissolved in bottem layer of the

pond. This salt to store the heat and with stand long time. The heat is tranfer to the

water throght the glass. The first layer to absorbe the

Most people know that fluids such as water and air rise when heated. Solar pond

stop this process when large quanties of salt are dissolved in the hot bottom layer

of the pond , making it too dense to the surface and cool.

Solar pond consist of three main layer. The top layer is cold and has little slat

content. The bottem layer is hot, 70-1000c (160-212

0F) , and very salty. Separating

these two layer is the important gradient zone. Here salt content increases with

depth as shown by the drawing . water in the gradient cant rise because the water

above it has less salt content and is therefore lighter. Similarly, water cant fall

because the water below it has a higher salt content and is heavier. Thus the stable

graient zone can act as a transparent insulator, permitting sunlight to be trapped in

the hot bottom layer, from which useful heat is withdrawn.

Inthis simplified description, no attempt is made to describe the

hydrodynamic phenomena which influence zone and interface stability, salt and

heat transport, and other complex behavior.

solar pond - project (autosaved)

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