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A

PROJECT REPORT

ON

Solar Water Distillator

Submitted by

Amol M Shah (110250119037)

Parin A Shah (110250119126)

Soham S Shelat (110250119121)

In fulfillment for the award of the degree

of

BACHELOR OF ENGINEERING

in

Mechanical Engineering

Indus Institute of Technology and Engineering-Rancharda

Gujarat Technological University, Ahmedabad

November, 2014

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Indus Institute of Technology and Engineering-Rancharda

At: Rancharda, Via: Thaltej, Ahmedabad - 382 115

CERTIFICATE

This is to certify that the project reports, submitted along with the project entitled

Solar water distillator has been carried out by Amol Shah(110250119037)

,Soham Shelat(110250119121),Parin Shah(110250119126) under my guidance

in partial fulfillment for the degree of Bachelor of Engineering in Mechanical

Engineering 7th

Semester of Gujarat Technological University, Ahmedabad

during the academic year 2014-15. These students have successfully completed

project activity under my guidance.

Prof. Kushal Mehta

Guide Mechanical Department IITE,Rancharda, Gujarat

Dr K G Sudhakar

Head of Department

Mechanical Department IITE-

Rancharda, Gujarat

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ACKNOWLEDGMENT

Every project big or small is successful largely due to the effort of a number of

wonderful people who have always given their valuable advice or lent a helping hand. I

sincerely appreciate the inspiration; support and guidance of all those people who have

been instrumental in making this project a success.

I take this opportunity to express my profound gratitude and deep regards to my guide

Prof. Kushal Mehta for her exemplary guidance, monitoring and constant

encouragement throughout the course of this thesis. The blessing, help and guidance

given by her time to time shall carry me a long way in the journey of life on which I am

about to embark.

I would also like to thanks all the faculty members for their critical advice and guidance

without which this project would not have been possible. I would like to thank non-

technical staff of the department who were helping me every time.

I am obliged to staff members of Umiya wood works, Ahmedabad for letting us use the

machinery required to build the model.

I have received enormous support as well as guidance from Soham shelat and Parin Shah

throughout my work. I am very much thankful for their deep insight guidance and

immense moral support for fulfilment of project report.

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ABSTRACT

The purpose of this project is to design a water distillation system that can purify

water from nearly any source, a system that is relatively cheap, portable, and

depends only on renewable solar energy.

The motivation for this project is the limited availability of clean water resources

and the abundance of impure water available for potential conversion into potable

water, In addition, there are many coastal locations where seawater is abundant

but potable water is not available. Our project goal is to efficiently produce clean

drinkable water from solar energy conversion.Distillation is one of many

processes that can be used for water purification. This requires an energy input as

heat, electricity and solar radiation can be the source of energy. When Solar

energy is used for this purpose, it is known as Solar water Distillation. Solar

Distillation is an attractive process to produce portable water using free of cost

solar energy. This energy is used directly for evaporating water inside a device

usually termed a Solar Still. Solar stills are used in cases where rain, piped, or

well water is impractical, such as in remote homes or during power outages.

Different versions of a still are used to desalinate seawater, in desert survival kits

and for home water Purification. For people concerned about the quality of their

municipally-supplied drinking water and unhappy with other methods of

additional purification available to them, solar distillation of tap water or

brackish groundwater can be a pleasant, energy- efficient option. Solar

Distillation is an attractive alternative because of its simple technology, non-

requirement of highly skilled labour for maintenance work and low energy

consumption.

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Table of Contents

Title page 1

Certificate 2

Acknowledgement 3

Abstract 4

Table of contents 5

List of figures 6

List of tables 7

Ch 1 Literature review 8

1.1 Water purification 9

1.1.1 Options for purification 10

1.1.2 Needs for purification 11

1.2 Solar water distillation 13

1.3 Basic concept 15

1.4 Working of solar still 17

1.5 Design types and performance 18

1.6 Capability 21

1.7 User experience 22

Ch 2 Model making 24

2.1 Construction of solar still 25

2.2 Details of different parts of system 26

Ch 3 Experimental data 29

3.1 Experiment 30

Ch 4 Conclusion 37

Ch 5 Future scope 39

Refrences 41

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List of Figures

Fig.1.1 Basic concept of Solar Water

Distillation

14

Fig.1.2 Working of Solar Still Plant 15

Fig.1.3 Layout of Solar Still Plant 16

Fig.1.4 Proposed model of solar still 25

Fig.1.5 Side walls of still 26

Fig.1.6 Glass assembled with box 27

Fig.1.7 Channel design 27

Fig.1.8 Working model 28

Fig.1.9 Passive design 36

Fig.1.10 Design drawing 36

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List of Tables

Table 1 Reading of the still 30

Table 2 Comparison of various materials 32

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CHAPTER 1

LITERATURE REVIEW

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1.1 Water Purification:-

It is the process of removing undesirable chemicals, biological contaminants, suspended solids

and gases from contaminated water. The goal is to produce water fit for a specific purpose.

Most water is purified for human consumption (drinking water), but water purification may

also be designed for a variety of other purposes, including meeting the requirements of

medical, pharmacological, chemical and industrial applications. In general the methods

used include physical processes such as filtration, sedimentation, and distillation,

biological processes such as slow sand filters or biologically active carbon chemical

processes such as flocculation and chlorination and the use of electromagnetic radiation

such as ultraviolet light.

1.1.1 Options for water purification:-

There are four possible ways of purifying water for drinking purpose:-

1. Distillation

2. Filtration

3. Chemical Treatment

4. Irradiative Treatment

Considering the areas where the technology is intended to be used we can rule out few

of the above mentioned methods based on the unavailability of materials or costs. Chemical

treatment is not a stand alone procedure and so is irradiative treatment. Both can act only

remove some specific impurities and hence can only be implemented in coordination with other

technologies.

This analysis leaves us with two methods Distillation and Filtration. By weighting the Positive and negatives of both the methods we decided to go by the first one. The most Important

considerations were that of complexity, higher maintenance and subsequent costs coupled with

need of other sophisticated supporting equipment

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1.1.2 Needs and Specifications of water purification:-

Our project centers on converting the roughly 99.6% of water that is, in its natural form,

undrinkable, into clean and usable water. After researching and investigation, we outlined our

needs to be the following:-

1. Efficiently produce at 2 gallons of potable water per day minimum

2. Able to purify water from virtually any source, included the ocean

3. Relatively inexpensive to remain accessible to a wide range of audiences

4. Easy to use interface

5. Intuitive setup and operation

6. Provide clean useful drinking water without the need for an external energy source 7. Reasonably compact and portable

Our aim is to accomplish this goal by utilizing and converting the incoming radioactive power

of the sun's rays to heat and distill dirty and undrinkable water, converting it into clean

drinkable water. A solar parabolic trough is utilized to effectively concentrate and increase the

solid angle of incoming beam radiation, increasing the efficiency of the system and enabling

higher water temperatures to be achieved.

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1.2 SOLAR WATER DISTILLATION

Solar energy is a very large, inexhaustible source of energy. The power from the sun

intercepted by the earth is approximately 1.81011

MW., which is many thousands times larger

than the present all commercial energy consumption rate on the earth. Thus in principle, solar

energy could supply all the present and future energy needs of the world on a continuous basis.

This makes it one of the most promising of all the unconventional

energy sources. In addition to its size, solar energy has two other factors in its favor. Firstly,

unlike fossil fuels and nuclear power, it is an environmentally clean source of energy.

Secondly, it is free and available in adequate quantity.

Solar water distillation is a solar technology with a very long history and

installations were built over 2000 years ago, although to produce salt rather than drinking

water. Documented use of solar stills began in the sixteenth century. An early large-scale

solar still was built in 1872 to supply a mining community in Chile with drinking water.

Mass production occurred for the first time during the Second World War when 200,000

inflatable plastic stills were made to be kept in life-crafts for the US Navy.

The energy required to evaporate water, called the latent heat of vaporisation of water,

is 2260 kilo joules per kilogram (kJ/kg). This means that to produce 1 litre (i.e. 1kg as the

density of water is 1kg/litre) of pure water by distilling brackish water requires a heat input of

2260 kJ. This does not allow for the efficiency of the system sued which will be less than

100%, or for any recovery of latent heat that is rejected when the water vapour is condensed. It

should be noted that, although 2260 kJ/kg is required to evaporate water, to pump a kg of

water through 20m head requires only 0.2kJ/kg. Distillation is therefore normally considered

only where there is no local source of fresh water that can be easily pumped or lifted.

Human beings need 1 or 2 litres of water a day to live. The minimum requirement for

normal life in developing countries (which includes cooking, cleaning and washing clothes) is

20 litres per day .Yet some functions can be performed with salty water and a typical

requirement for distilled water is 5 litres per person per day. Therefore 2m2

of solar still are

needed for each person served. Solar stills should normally only be considered for

removal of dissolved salts from water. For output of 1m3/day or more, vapour compression

or flash evaporation will normally be least cost.

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Solar distillation systems can be small or large. They are designed either to serve the

needs of a single family, producing from to 3 gallons of drinking water a day on the

average, or to produce much greater amounts for an entire neighbourhood or village. In

some parts of the world the scarcity of fresh water is partially overcome by covering shallow

salt water basins with glass in greenhouse-like structures. These solar energy distilling plants

are relatively inexpensive, low-technology systems, especially useful where the need for

small plants exists. Solar distillation of potable water from saline (salty) water has been

practiced for many years in tropical and sub-tropical regions where fresh water is scare.

However, where fresh water is plentiful and energy rates are moderate, the most cost-effective

method has been to pump and purify.

Solar distillation is a relatively simple treatment of brackish (i.e. contain dissolved salts)

water supplies. In this process, water is evaporated; using the energy of the sun then the

vapour condenses as pure water. This process removes salts and other impurities. Solar

distillation is used to produce drinking water or to produce pure water for lead acid batteries,

laboratories, hospitals and in producing commercial products such as rose water. It is

recommended that drinking water has 100 to 1000 mg/l of salt to maintain electrolyte levels

and for taste. Some saline water may need to be added to the distilled water for acceptable

drinking water.

Generally, solar stills are used in areas where piped or well water is impractical. Such

areas include remote locations or during power outages .Distillation are therefore normally

considered only where there is no local source of fresh water that can be easily pumped or

lifted. One of the main setbacks for solar desalination plant is the low thermal efficiency and

productivity. In areas that frequently loss power, Solar stills can provide an alternate source

of clean water. A large use of solar stills is in developing countries where the technology to

effectively distill large quantities of water has not yet arrived.

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1.2.1 BASIC CONCEPT OF SOLAR WATER DISTILLATION

The basic principles of solar water distillation are simple yet effective, as distillation

replicates the way nature makes rain. The sun's energy heats water to the point of

evaporation. As the water evaporates, water vapor rises, condensing on the glass surface

for collection. This process removes impurities such as salts and heavy metals as well as

eliminates microbiological organisms. The end result is water cleaner than the purest

rainwater. The Solar still is a passive solar distiller that only needs sunshine operate.There

are no moving parts to wear out.

The distilled water from a Solar still does not acquire the "flat" taste of commercially

distilled water since the water is not boiled (which lowers pH). Solar stills use natural

evaporation and condensation, which is the rainwater process. This allows for natural pH

buffering that produces excellent taste as compared to steam distillation. Solar stills can easily

provide enough water for family drinking and cooking needs.

Solar distillers can be used to effectively remove many impurities ranging from salts to

microorganisms and are even used to make drinking water from seawater. Solar stills have

been well received by many users, both rural and urban, from around the globe. Solar solar

distillers can be successfully used anywhere the sun shines.

The Solar solar stills are simple and have no moving parts. They are made of quality materials

designed to stand-up to the harsh conditions produced by water and sunlight. Operation is

simple: water should be added (either manually or automatically) once a day through the still's

supply fill port. Excess water will drain out of the overflow port and this will keep salts from

building up in the basin. Purified drinking water is collected from the output collection port.

Supply Fill Port:

Water should be added to the still via this port. Water can be added either manually or

automatically. Normally, water is added once a day (in the summer it's normally best to fill in the

late evening and in the winter, in the early morning). Care should be taken to add the water at a

slow enough flow rate to prevent splashing onto the interior of the still glazing or overflowing

into the collection trough.

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Overflow Port:

Once the still basin has filled, excess water will flow out of this port. Solar recommends three

times daily distilled water production to be allowed to overflow from the still on a daily basis

to prevent salt build-up in the basin. If your still produced 2 gallons of product water then

you should add 6 gallons of fresh feed water through the fill port. If flushed like this on a

daily basis, the overflow water can be used for other uses as appropriate for your feed

water (for example, landscape watering).

Distilled Output Collection Port:

Purified drinking water is collected from this port, typically with a glass collection container.

Stills that are mounted on the roof can have the distillate output piped directly to an interior

collection container. For a newly installed still, allow the collection trough to be self-cleaned by

producing water for a couple of days before using the distillate output

Fig.1.1 Basic concept of Solar Water Distillation

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1.3 WORKING OF SOLAR STILL

Fig.1.2 Working of Solar Still

Solar stills are called stills because they distill, or purify water. A solar still operates on the

same principle as rainwater: evaporation and condensation. The water from the oceans

evaporates, only to cool, condense, and return to earth as rain. When the water evaporates, it

removes only pure water and leaves all contaminants behind. Solar stills mimic this natural

process.

A solar still has a top cover made of glass, with an interior surface made of a waterproof

membrane. This interior surface uses a blackened material to improve absorption of the sun's

rays. Water to be cleaned is poured into the still to partially fill the basin. The glass cover

allows the solar radiation (short-wave) to pass into the still.

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The water begins to heat up and the moisture content of the air trapped between the water

surface and the glass cover increases. The base also radiates energy in the infra-red region

(long-wave) which is reflected back into the still by the glass cover, trapping the solar energy

inside the still (the "greenhouse" effect). The heated water vapor evaporates from the basin

and condenses on the inside of the glass cover. In this process, the salts and microbes that were

in the original water are left behind. Condensed water trickles down the inclined glass cover

to an interior collection trough and out to a storage bottle. There are no moving parts in Solar

still and only the suns energy is required for operation.

The still is filled each morning or evening, and the total water production for the day is

collected at that time. The still will continue to produce distillate after sundown until the

water temperature cools down. Feed water should be added each day that roughly exceeds

the distillate production to provide proper flushing of the basin water and to clean out excess

salts left behind during the evaporation process.

Fig.1.3 Layout of Solar Still Plant

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1.4 Design objectives for an efficient solar still:-

For high efficiency the solar still should maintain:-

a high feed (undistilled) water temperature

a large temperature difference between feed water and condensing surface Low vapour leakage.

A high feed water temperature can be achieved if:-

A high proportion of incoming radiation is absorbed by the feed water as heat. Hence low absorption glazing and a good radiation absorbing surface are required

heat losses from the floor and walls are kept low The water is shallow so there is not so much to heat.

A large temperature difference can be achieved if:-

the condensing surface absorbs little or none of the incoming radiation Condensing water dissipates heat which must be removed rapidly from the condensing surface by, for

example, a second flow of water or air, or by condensing at night.

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1.4.1 Some problems with solar stills which would reduce their

efficiency include:-

Poor fitting and joints, which increase colder air flow from outside into the still Cracking, breakage or scratches on glass, which reduce solar transmission or let in air

Growth of algae and deposition of dust, bird droppings, etc. To avoid this the stills need to be cleaned regularly every few days

Damage over time to the blackened absorbing surface.

Accumulation of salt on the bottom, which needs to be removed periodically

The saline water in the still is too deep, or dries out. The depth needs to be maintained at around 20mm

1.5 Design types and their performance:-

Single-basin stills have been much studied and their behavior is well understood.

Efficiencies of 25% are typical. Daily output as a function of solar irradiation is greatest in

the early evening when the feed water is still hot but when outside temperatures are falling.

Multiple-effect basin stills have two or more compartments. The condensing surface of

the lower compartment is the floor of the upper compartment. The heat given off by the

condensing vapour provides energy to vaporize the feed water above. Efficiency is therefore

greater than for a single-basin still typically being 35% or more but the cost and complexity are

correspondingly higher.

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 can be tilted so that the

feed water presents a better angle to the sun (reducing reflection and presenting 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.

Simple wick stills are more efficient than basin stills and some designs are claimed to cost less

than a basin still of the same output.

Emergency still - To provide emergency drinking water on land, a very simple still can be

made. It makes use of the moisture in the earth. All that is required is a plastic cover, a bowl or

bucket, and a pebble.

Hybrid designs - There are a number of ways in which solar stills can usefully be

combined with another function of technology. Three examples are given:

a) Rainwater collection:-By adding an external gutter, the still cover can be used for rainwater collection to supplement the solar still output.

b) Greenhouse-solar still:-The roof of a greenhouse can be used as the cover of a still.

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c) Supplementary heating: - Waste heat from an engine or the condenser of a refrigerator can be used as an additional energy input.

After going through the various existing designs of solar stills there are a few facts :

The efficiency of single stage still is around 25%.

The efficiency of multistage stills is higher than 35%.

Mostly people use three staged stills because for more stages the cost outweighs the utility.

Most of the losses can be attributed to heat transfer losses.

Thermal losses are mostly in form of conduction and convection and very little by radiation owing to low temperatures. So we can assume radiative losses to be negligible.

Also the cost of a solar still which produces reasonable amount of purified water is high.

The cost of water produced by the still is high. This fact attributes to almost negligible

penetration of solar stills in Indian villages. While persuing and pondering about the

ways to reduce costs the first factor that comes to mind is why not increase the

efficiency. But as we all know this is much easier said than done. After giving it a

considerable thought we came up with a design that can greatly improve the efficiency of

a solar water distillation system by minimizing thermal losses.

The equations governing the heat transfer rates are:-

a. Conduction

Q = - k A dT / dx

b. Convection

Q = h A ( Tsurface- Tambient )

Both the losses are greatly dependant on the area and temperature difference between the

medium i.e., water and ambient. Hence if we can reduce temperature of the whole system we

can reduce the heat loss and hence improve the efficiency.

But reducing operating temperature will come at the cost of lower rated of evaporation and

consequently lower rated of condensation leading to slower distillation. So now the problem

boils down to increasing the rated of evaporation at lower temperature.

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(Mass loss rate) / (Unit area) = (Vapor Pressure - Ambient Partial Pressure) * sqrt (

(Molecular Weight)/(2*pi*R*T))

The Vapor Pressure of a liquid at a given temperature is a characteristic property of that liquid.

Vapor pressure of a liquid is intimately connected to boiling point.

Vapor Pressures are influenced by Temperature logarithmically and this relationship is defined

with the Clausius Clapyron Equation:

Log P2 / P1 = Delta H vaporization [ 1 / T1 - 1/T2] / 2.303 ( R)

where:

R = universal gas law constant = 8.31 J/mol-K = 8.31 X 10-3 Kj / mol-K P1 and

P2 = vapor pressure at T1 and T2

T1 and T2 = Kelvin Temperature at the initial state and final state At

373K the pressure is 1 atm.

We all know that boiling takes place when the ambient temperature equals that of the vapor

pressure of the liquid. This means that we can increase the rate of evaporation by reducing the

pressure of the vessel. This will ensure higher rates of evaporation even at low temperatures.

Constructing a solar water distiller using available utensils like plastic for casing, aluminum for

absorption of heat, glass and the thermocol for insulation. Got the temperature of water up to 60

degrees and 100 ml of distilled water in 4 hours.

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1.6 CAPABILITIES

A solar still operates using the basic principles of evaporation and condensation. The

contaminated feed water goes into the still and the sun's rays penetrate a glass surface causing

the water to heat up through the greenhouse effect and subsequently evaporate. When the

water evaporates inside the still, it leaves all contaminants and microbes behind in the basin.

The evaporated and now purified water condenses on the underside of the glass and runs into

a collection trough and than into an enclosed container. In this process the salts and microbes

that were in the original feed water are left behind. Additional water fed into the still flushes

out concentrated waste from the basin to avoid excessive salt build-up from the evaporated salts.

A solar still effectively eliminates all waterborne pathogens, salts, and heavy metals. Solar

still technologies bring immediate benefits to users by alleviating health problems associated

with water-borne diseases. For solar stills users, there is a also a sense of satisfaction in having

their own trusted and easy to use water treatment plant on-site.

Solar still production is a function of solar energy (insolation) and ambient temperature. Typical

production efficiencies for single basin solar stills on the Border are about 60 percent in the

summer and 50 percent during the colder winter. Single basin stills generally produce about 0.8

liters per sun hour per square meter.

Given the smaller product water output for a solar still, the technology calls for a different

approach to providing purified water in that it only purifies the limited amounts of water that

will be ingested by humans. Water used to flush the toilet, take a bath, wash clothes, etc. does

not need to meet the same high level of purity as water that is ingested, and thus does not need

to be distilled.

Solar stills have proven to be highly effective in cleaning up water supplies and in providing safe

drinking water. The effectiveness of distillation for producing safe drinking water is well

established and long recognized. Distillation is the only stand alone point- of-use (POU)

technology with NSF (National Sanitation Foundation) certification for arsenic removal,

under Standard 62. Solar distillation removes all salts and heavy metals, as well as

biological contaminants.

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1.7 USER EXPERIENCES

Surveys were conducted on user satisfaction with project participants receiving cost- shared

solar distillers . Users were nearly unanimous that owning a solar still was good for them. Some

owners prized the idea of using alternative, clean energy to achieve their purposes, while at

the same time leaving only a small footprint on the planet. All were very enthused about the economic benefits of using a solar distiller. They found that paying a relatively low price for a

still was a favorable alternative to having to buy water on a regular basis with no end in sight to

this routine. Others valued the independence and fascination they experienced from being

involved in the production of their own purified water. Most colonias residents often do not

trust their local water supply in those cases when there is one available (e.g., Columbus).

While many have noted a concern over local water supply color or odor, the overwhelming

characteristic that gains their attention is poor taste. There is a good deal of concern with taste,

and most of those interviewed noted that one of the reasons for wanting a water purification

system was to improve the taste of their local water supply. Since many of the local water

supplies are high in salts and minerals (e.g., iron or sulphur), they often have a marginal or

poor taste. The solar stills were considered useful by colonia residents to improve drinking

water taste.

Solar distillers were able to meet all of the drinking and cooking water needs of a household. Not

all of the households receiving solar stills through pilot projects had stills optimally sized to

meet all of their wintertime water production needs, but about 40 percent of the households

were completely satisfied with their still water production.

All households had sufficient water during the high summertime production period, and it was

during the wintertime where some families had insufficient still water.

Generally, it appears that for most Border households about 0.5 m2 meter of solar still is

needed per person to meet potable water needs consistently throughout the year. Those

households with insufficient wintertime still water production typically had

0.35 m2 or less of still area per person. Survey results clearly indicate that only about a third of

colonias residents are willing or able to pay the full price of the solar still up front, because most

simply could not afford the higher up-front capital cost. However, interest mounted greatly when

the possibility of financing was mentioned. Thus, water districts and others interested in

providing potable water to Border colonias should consider offering an option for still

financing. To bolster interest, a clear, easy-to-follow breakdown of cost payback should be

provided. Prospective customers interest is peaked when they realize that even at full price, a

solar still can pay for itself in less

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than two years as compared to purchasing bottled water. Some prospective customers

would be delighted to know that savings over a decade or more could be substantial

and amount to thousands of dollars.

Almost all of those surveyed were using their solar stills regularly, thus now

meeting most or all of their drinking water and cooking water supply needs via solar

distillation. Occasionally, still users had to supplement their still supply with store-bought

water, especially in the winter, when still production decreases to about half of

summertime production. Yet the need for purchasing bottled water from a store was

greatly mitigated in all cases. Solar still savings were approximately $150 - $200 a year

per household instead of purchasing bottled water.

Solar still technology has gradually improved over the past decade along the Border.

The greatest problem for the first generation stills designed by EPSEA in the mid-

1990s (an improvement on the original McCracken solar still) was that when they dried out, the inner membrane silicone lining would outgas. This in turn deposited a fine

film on the underside of the glass, causing the water droplets to bead up and fall back

into the basin rather than trickle down the glass to the collection trough and thus still

water production drops dramatically (about 80% or more drop). The first still used a food

grade silicone and were made out of plywood and concrete siding. It was found that the

stills (3 x 8) were often producing far more water than the users needed, especially in the summer. As time evolved, a second generation solar still was developed made out

of aluminum and smaller (3 x 6 and 3 x 3). The still was lighter, but expensive to build.

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CHAPTER 2

MODEL MAKING

25

2.1 Construction of Solar Still

Figure.1.4 Proposed Model of Solar Distillation System

The base of the solar still is made of G.I. box of dimension (4 x 2 x 10 cm). This box is embedded into another box of wood shown in figure 1. Here length L= 65 cm,

Breath B= 125cm, Height H= 30 cm. and at opposite side = 13 cm, Angle = 150 . This also contains same box of thermocol inside it between the G.I box and wooden

box. The thermocol is having 15 cm thickness. The channel is fixed such that the water

slipping on the surface of the glass will fall in this channel under the effect of gravity.

A frame of fibre stick is fixed with the wooden box so that glass can rest on it. This

completes the construction of the model.

The holes for the inlet of water, outlet of brackish water and outlet of pure water is

made as per the convenience. We have made the outlet of brackish water at right

bottom of the model (seeing from front of the model), outlet of the pure water at the

end of the channel and inlet at the right wall above the outlet.

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2.2 Details of Different Parts of the System

Still Basin: It is the part of the system in which the water to be distilled is kept.It is

therefore essential that it must absorb solar energy. Hence it is necessary that the

material have high absorbtivity or very less reflectivity and very less transmitivity.

These are the criterias for selecting the basin materials.Kinds of the basin materials that can be used are as follows: 1. Leather sheet, 2. Ge silicon, 3. Mild steel plate, 4. RPF

(reinforced platic) 5. G.I. (galvanised iron). We have used blackened galvanised iron

sheet(K= thermal conductivity= 300W/m0C)

(3mm thick).( SIZE:: 4 X 2 X 10 cm BOX OF G.I.).

Side Walls: It generally provides rigidness to the still. But technically it provides

thermal resistance to the heat transfer that takes place from the system to the

surrounding. So it must be made from the material that is having low value of thermal

conductivity and should be rigid enough to sustain its own weight and the weight of the

top cover (refer fig.no.2).

Different kinds of materials that can be used are: 1) wood , 2) concrete, 3) thermocol,

4) RPF (reinforced plastic).

For better insulation we have used composite wall of thermocol (inside) and wood

(outside). (Size:: wood(k= thermal conductivity=0.6W/m0C):-- 8 mm thick,

thermocol(k= thermal conductivity=0.02W/m0C):--- 15 mm thick).

Figure.1.5 Side Walls for Solar Still

Top Cover: The passage from where irradiation occurs on the surface of the basin is

top cover. Also it is the surface where condensate collects. So the features of the top

cover are: 1) Transparent to solar radiation, 2) Non absorbent and Non-adsorbent of

water ,3) Clean and smooth surface. The Materials Can Be Used Are: 1) Glass, 2)

Polythene.

We have used glass (3mm) (figure 3)thick as top cover having rubber tube as

frame border. (size: ---- 4 x 2cm).

27

Fig1.6 Solar Still Glas withCover

Channel: The condensate that is formed slides over the inclined top cover and falls in

the passage, this passage which fetches out the pure water is called channel. The

materials that can be used are: P.V.C., 2) G.I. , 3) RPF .

We have used P.V.C channel (figure.4)(size:: 4.5 X 1 cm).

Figure.1.7 Solar Still Channel Design

Supports for Top Cover: The frame provided for supporting the top cover is an

optional thing. I.e. it can be used if required. We have used fibre stick as a support to

hold glass (size :: 5 mm X 5mm).

The only change in our model is that we have to make the model as vacuumed

as possible. So we have tried to make it airtight by sticking tape on the corners of the

glass and at the edges of the box from where the possibility of the leakage of inside hot

air is maximum.

28

Figure.1.8 Working model of solar distillation system

29

CHAPTER 3

EXPERIMENTAL DATA

30

3.1 Experiment

Experiment is performed from 10:00am to 04:00pm in winter season.

Readings taken for still:

Table 1 represents the reading taken for solar still.

Table. 1 Reading for Solar Still

Time Temp of Water 0C

10:00 AM 20 10:45 AM 26 11:15 AM 33 1:30 PM 49 3:00 PM 53 4:00 PM 46

Observations:

Time taken for drop to come to channel = 1 hour

Time taken for drop to come out of channel = 0.5 hour

Amount of brackish water poured initially = 14 litre

Amount of pure water obtained at the end of the exp. = 1.5 litre

Temperature of the condensate = 29 0C

TDS of purified water = 81 ppm

31

Efficiency of Still: The theoretically obtained amount of pure water = 2.33 litre The

practically obtained amount of pure water = 1.5 litre.

Efficiency=(actual amount of pure water)/(theoretical amount of pure water)*100

= (1.5 / 2.33) *100

= 64.37 %

Results

From the graph 1, we can conclude that the increase in temperature and hence the

evaporation is maximum in the period of 11:15 am to 1:30 pm. The maximum temperature

achieved is 530c which is at 1:30 pm. then the temperature decreases.

The aim of our experiment was to get pure water from the brackish water available. The

brackish water we have supplied was 14 litres and at the end of the experiment we got 1.5

litres. The experiment was carried out in winter season.

The TDS level of purified water obtained is 81 PPM. So the water obtained is potable.

Theoretically, the experiment should fetch out 2.33 litres. So the efficiency of the system is

6%.

32

COST ANALYSIS & MATERIALS

Table 2Comparison of Various Materials Used in Solar Basin Construction

Materials:-

1. The side and bottom walls need to be insulated. This can be achieved by using multilayered insulator. Glass wool will be sand-witched between two metallic plates. This

will ensure negligible heat loss to the surroundings.

2. The main frame is composed of steel owing to its corrosion resistance, low weight, long life and easy cleanability.

3. The outside of the complete distiller is coated with carbon black to increase absorption of radiation.

4. The cover on the top is made of tempered glass so that the birds cant see their

reflection and hence avoid nuisance.

Cost Analysis:-

Total cost of wood box = Rs 500

Cost of crushed hay and sawdust = Almost free Cost of

carbon black paint = Rs 300

Cost of tempered glass = Rs 500 Cost of

pipe fitings = 100

Cost of insulation and sealing = Rs. 250

Cost of the hoisting mechanism and other auxiliaries = Rs 500

Cost of Report Writing: Rs. 500

Material Durability Cost Availibil

ity

Skill

Needed

Cleaning Portabili

ty

Toxicity

Enamled

steel

High High Low Low High Medium Low

EPDM

rubber

High High Low Low High High Low

Butyl

rubber

High High Low Low High High Low

Asphalt High Mediu

m

Medium Medium Medium Medium Medium

Asbestos High Mediu

m

Low Medium Medium Medium High

Wood Low Low Low Medium Medium Medium Low

33

(Typing, Editing, Color Printing,Hard Binding)

Net cost of the Project = Rs 2800

The per-liter cost of solar-distilled water can be calculated as follows:

estimate the usable lifetime of the still;

add up all the costs of construction, repair and maintenance (including labor)

over its

divide that figure by the still's total expected lifetime output in liters.

Such a cost estimate is only approximate since there are large uncertainties in both the lifetime and the yield estimates. Costs are usually considerably higher than

current water priceswhich explains why solar backyard stills are not yet marketed widely in India

34

.

Assembling and manufacture:-

Fabrication of the whole unit is pretty straight forward and involves metal cutting, welding, glass

cutting, sealing, painting and drilling. All these processes can be done at any local workshop

using simple machines lathe, drill, welding, milling etc.

The steps in the process of assembling are outlined as follows:

1. The outer box will be fabricated first. It will be made of double wall and will be filled with glass wool to provide insulation.

2. The stages will be fabricated second the collector holes will be made at the time of fabrication. Finally the stages will be assembled inside the outer covering.

3. The collector tubes are then made and attached to the lowermost stage.

4. The holes are provided for

a. Collecting distilled water

b. Transporting saline water

c. To attach the pump

5. The whole system is sealed using sealant to prevent the air from leaking in from the atmosphere.

The cost of construction for a passive solar still is considerably cheaper than a more complex

humidification/condensation flow through system. All that is required is a large insulated box

with solar absorbing material in the basin, and a transparent glazing.

Because the box is not under any loading, most insulating foam boards such as expanded

polystyrene, extruded polystyrene, and polyisocyanurate board can provide structural rigidity

and no other materials will be needed. The cost of construction components is listed below.

Box Structure/Insulation:

Extruded polystyrene foam has the best combination of light weight, rigidity, and

low cost. Foam boards of 2 thickness measuring 4x8 can be purchased

35

from sources such as Univfoam and Foam-Control. Three boards are required for the

construction a solar still with base dimensions of 1x2.25 m, with a 20 inclined slope glazing.

The maximum side height is 0.50 m, the minimum side height is 0.14 m.

Glazing:

One solid piece of polycarbonate measuring 1x2.25m will be required for the

glazing. This can be purchased from sources such as Eplastics and USplastic for a 1/16 thick sheet measuring 4x8. The excess from this sheet will be used to construct the catch for the distilled water.

Solar Radiation Absorber:

Another sheet of the same polycarbonate sheet used for the glazing can be painted

black and used as a solar heat absorber.

A picture of the passive solar still is shown below in Fig. 10, and dimensions are shown

in Fig. 1.9 The dimensions of the water refill port are arbitrary, or if tube filling is chosen as

the filling mode, it can be omitted. The actual catch for distill water is not shown, but

simply consists of a strip of polycarbonate fixed to the sloped glazing near the bottom, to

catch and direct the condensate out through the drip spout.

36

Figure 1.9 Passive Solar Still Design

Figure 1.10 Design Drawing of Solar Still, Dimensions in cm.

37

CHAPTER 4

CONCLUSION

38

Distillation is a method where water is removed from the contaminations rather than to remove

contaminants from the water.Solar energy is a promising source to achieve this.This is due

to various advantages involved in solar distillation. The Solar distillation involves zero

maintenance cost and no energy costs as it involves only solar enegy which is free of cost.

It was found from the experimental analysis that increasing the ambient temperature

from 32C to 47C will increase the productivity by approx 12 to 23%, which shows that

the system performed more distillation at higher ambient temperatures. When inverted type

absorber plate was used thermal efficiency of single slope solar still was increased by 7 %.

It was observed that when the water depth increases from 0.01m to 0.03m the productivity

decreased by 5%.These results show that the water mass (water depth) has an intense effect

on the distillate output of the solar still system.

Solar still productivity can also increase by use of reflector by 3%. The use of the mirror

reflector will increase the temperature of the solar still basin; such an increase in the

temperature is because of the improvement in solar radiation concentration.

The solar radiation increase from 0 MJ/m2 /h to 6 MJ/m2 /h has increased the productivity of

the still by 15 to 32%. However the increase of the solar radiation parameter will increase

the solar energy absorbed by the basin liner.

The main disadvantage of this solar still is the low productivity or high capital cost per

unit output of distillate.This could be improved by a number of actions, e.g. injecting black dye

in the seawater,using internal and external mirror,using wick,reducing heat conduction

through basin walls and top cover or reusing the latent heat emitted from the condensing vapour

on the glass cover.Capital cost can be reduced by using different designs and new materials

for construction of solar stills.

39

CHAPTER 5

FUTURE SCOPE

40

According to a World Bank report, 80% of communicable diseases in India are water related and with a population of 1.17 billion, only 15% have access to water fit for

consumption purposes. Also, ground water sources have been over-exploited, which has

caused the levels of mineral contaminants to increase dramatically. For example, in places

such as Rajasthan, Gujarat and Andhra Pradesh, the population is consuming water that has

high fluoride content which in turn will lead to increasing health risks such as mass

poisoning.

Solar distillation is a proven technology for water disinfection and the system can be customized from one person to community sized systems. They have a long life span of

about 20 years and generally do not require moving parts.The water purification business in

India is undergoing major changes, not just in terms of technology, but also in terms of

pricing and competition. The drivers of change include scarcity of clean drinking water, low

penetration of water purifiers, increasing urbanization, and waterborne diseases. The main

challenges are the lack of standards (for manufacturers) and low awareness levels amongst

potential users. The market has also started evolving for a category of consumers who do

not have access to running water electricity and lower price point products.

As almost 30% of rural India has no access to safe drinking water, consistent electricity source or even the financial means to afford the relatively expensive modes of water

purifying products. Therefore providing them with solar water purifiers, which makes use

of solar photo voltaic systems would be a step in the right direction as an access to clean,

safe, consumable water. There is an untapped opportunity in the rural areas but it is

definitely an effort for the long haul.

41

References

M.A.S. Malik, G.N Tiwari, A. Kumar and M.S. Sodha. Solar Distillation, Pergamon Press, Oxford, UK,

1982.

A. Kumar, A. Kumar, G.D. Sootha and P. Chaturvadi, Performance of a multi-stage distillation system using a flat-plate collector, Extended Abstract, ISES Solar World Congress, Kobe, Japan, 1989.

Akash BA, Mohsen MS, Osta O and Elayan Y ,Experimental evaluation of a single-basin solar still using

different absorbing materials,renewable energy- 14, 1998,307-310.

B.B.sahoo, N.Sahoo, P.Mahanta, L.Borbora, P.kalita, Performance assesment of solar still using blackened surface and thermocole

insulation , October 2007.

Garg H.P and J.Prakash, solar energy, Tata McGraw Hill Publishing Co. 2008.

Rai G.D. Non- conventional energy sources ,

Khanna Pub. 4th Ed, 2000. [7] Tiwari G.N

solar energy, Narosa Publishing House, 2002.

R.k.Rajput Heat and mass Transfer S.Chand publication.

David incropera Heat and Mass Transfer Wan Willey Publication