PREFACE

In Final year of Mechanical Engineering every student has undertaken one major project .

While selecting the subject or project, the following characteristics should be kept in mind.

1. It should test the skill attitude and the group range of knowledge of every student.

2. It should consider the local , social and industrial people and try to the fulfill it.

3. Preference should be given to the student and selection of project should match their

program me performance considering all their ability to works.

CONTENTS

Index of Report

Abstract

Nomenclature

List of tables

List of charts

Chapter-1 Introduction

1.1 Introduction

1.2 Principle

1.3 Types of Solar Still

1.4 Application

1.5 Scope of Work

1.6 Organization

Chapter-2 Literature Review

2.1 Introduction

2.2 Literature Review

2.3 Concluding Remark

Chapter-3 Theoretical Analysis

3.1 Introduction

3.2 Theoretical Analysis

3.3 Equations

3.4 Parameter

3.5 Dimensions

3.6 Various Losses

3.7 Various Formulas

3.8 Comparison

Chapter-4 Experimental Set-up and Planning of Experiment

4.1 Introduction

4.2 Material Selection

4.3 Requirement of m/c tools and Measuring Equipments

4.4 Experimental setup

Chapter-5 Costing

5.1 Defination

5.2 Aim of Costing

5.3 Purchase material and Labour cost

5.4 Final cost of BTSS

Chapter-6 Results and Discussion

6.1 Introduction

6.2 Results and Discussion

Chapter-7 Conclusion

7.1 Future Scope of Work

7.2 Conclusion

1. Appendix

2. References

NOMENCLATURE

Symbols Descriptions Units

H Heat transfer Coefficient W/m2

Ha Convective heat transfer coefficient W/m2

Q heat transfer in. W/ m2

T Temperature of the body in K

Q Rate of heat transfer KJ/sec.

M mass flow rate kg/sec

Cp specific heat KJ/Kg.K

ΔT Temperature Difference K

U The overall heat transfer coefficient W/m2.K

As Surface area m2

K Conductivity W/m.K

Ts Temperature of the surface fluid in K

Ta Ambient temperature in K

Tt Top cover temperature𝛿 K

V Velocity of wind m/s

L Length of tube m

D Diameter of tube m

𝜗 Kinematic viscocity m2/sec

Greek Symbols

σ The Stefan-Boltzmann Constant = 5.6703 X 10-8 W/ m2 k4

W/ m2 k4

ρ Density Kg/m3

Є Emissivity

𝛿 Insulation thickness m

Suffix

W BTSS wall, wind Velocity

H Hot

C Cold

A Ambient

F Fluid

R Radiation

0 Out side

CHAPTER 1: INTRODUCTION

1.1 INTRODUCTION

Clean drinking water is a basic human need. Many people, especially in developing countries, do not have access to clean drinking water. Water that is dirty or salty is undrinkable, and untreated water that looks clean is likely to have bacteria and organisms that cause sickness

and disease.

We are selecting this project for water purification by solar energy. Solar energy is non

conventional energy so it’s cheap. Also an availability of water purifier in market is very costly

compare with solar still. Solar still are useful to convert radiation energy of sun in easily.

Several kinds of very practical solar energy systems are in use today. They also illustrate

the two basic methods of harnessing solar energy: solar thermal systems, and solar electric

systems. The solar thermal systems convert the radiant energy of the sun into heat, and then use

that heat energy as desired.

A solar still is a device that produces clean, drinkable water from dirty water using the energy from the sun.

Solar still uses the heat of the sun directly in a simple piece of equipment to purify water.

The equipment, commonly called a solar still, consists primarily of a shallow basin with a

transparent glass cover. The sun heats the water in the basin, causing evaporation. Moisture r ises,

condenses on the cover and runs down into a collection trough, leaving behind the salts,

minerals, and most other impurities, including germs.

Solar stills are used in cases where rain, piped, or well water is impractical, such as in remote homes or during power outages. It is targeted areas that frequently lose power for a few

days; solar distillation can provide an alternate source of clean water.

Although it can be rather expensive to build a solar still that is both effective and long-

lasting, it can produce purified water at a reasonable cost if it is built, operated, and maintained

properly.

Here focuses mainly on small-scale box-type solar stills as suppliers of potable water for

families and other small users.

1.2 PRINCIPLE

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 still

mimic this natural process.

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, which is mostly absorbed by the blackened

base. 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.

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 pasteurized 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.1.1: principle of box type solar still

1.3 COMPARISON BETWEEN SOLAR STILL AND SOLAR COOKER

The reflection losses from water and basin above in the still and cooker.

Single glass cover of still has more loss of heat; hence the cooker has two layer of glass

cover, which reduces the heat loss from surface. The cooker can be used for pasteurization of water by keeping water in a box.

The solar still gives continue supply of water, but cooker can be used for both the purpose by few changes.

The green house effect is used as basic principle in both cooker and still, but the cooker is

proved more efficient to absorb heat of solar energy and maintain it for long time.

The temperature raised in solar cooker is higher due to its well insulated cover design and arrangement of reflector glass.

Usually the solar still is bigger than solar cooker, the outer surface of the glass is more exposed to air causing more surface heat loss.

1.4 TYPES OF SOLAR STILLS

There are several different types of solar stills.

Pit Type

The most basic is the pit type, which is most appropriate for emergency survival situations because it has a very low productivity. See Figure 1.2 for a diagram of the pit still.

Fig.1.2: Diagram of a pit type solar still.

Box Type

The basin or box still is the most complex type. There are many different variations, but the two main categories of basin stills are single and double sloped. Figure 2 shows a picture of a single

sloped basin still and Figure 3 shows the double sloped still.

Fig.1.3: Diagram of a single sloped box Solar still

Double Slopped Still

The double sloped basin still is a similar but has two sloped pieces of glass rather than one.

Fig.1.4: Diagram of a double sloped basin Solar still

The benefits of the basin solar still are that it can produce several liters of water per square meter of still, per day. With an upfront capital cost to invest in good materials, this still can be built sturdy enough to operate faithfully with an efficiency of 30-60% for as long as 20 years.

Concentrating Collector Still

A concentrating collector still, as shown in Figure, uses parabolic mirrors to focus

sunlight onto an enclosed evaporation vessel. This concentrated sunlight provides extremely high temperatures which are used to evaporate the contaminated water. The vapor is transported to a separate chamber where it condenses, and is transported to storage. This type of still is capable of

producing from .5 to .6 gallons per day per square foot of reflector area. This type of output far surpasses other types of stills on a per square foot basis. Despite this still's outstanding

performance, it has many drawbacks; including the high cost of building and maintaining it, the need for strong, directs sunlight, and its fragile nature.

Fig.1.5: Diagram of concentrating collector Solar still

Multiple Tray Tilted Still

A multiple tray tilted still (Figure 1.6), consists of a series of shallow horizontal black trays enclosed in an insulated container with a transparent top glazing cover. The vapor

condenses onto the cover and flows down to the collection channel for eventual storage.

This still can be used in higher latitudes because the whole unit can be tilted to allow the sun's rays to strike perpendicular to the glazing surface. The tilt feature, however, is less

important at and near the equator where there is less change in the sun's position over the still.

Even though efficiencies of up to 50 percent have been measured, the practicality of this design remains doubtful due to:

the complicated nature of construction involving many components;

Increased cost for multiple trays and mounting requirements.

Fig.1.6: Diagram of Multiple Tray Tilted Still

Tilted Wick Solar Still

A tilted wick solar still draws upon the capillary action of fibers to distribute feed water over the entire surface of the wick in a thin layer. The water is then exposed to sunlight. (See

Figure)

Fig.1.7: Diagram of Tilted Wick Solar still

A tilted wick solar still allows a higher temperature to form on this thin layer than can be expected from a larger body of water. This system is as efficient as the tilted tray design, but its

use in the field remains questionable because of:

Increased costs due to mounting requirements and essential insulation;The need to frequently clean the cloth wick of built-up sediments, highlighting the need for an operable glazing cover;

The need to replace the black wick material on a regular basis due to sun bleaching and physical deterioration by ultra-violet radiation;

Uneven wetting of the wick which will result in dry spots, leading to reduced efficiency; and

The unnecessary aspect of the tilt feature except where it is required higher latitudes.

1.5 PASTEURIZATION

What is the Pasteurization process?

Definition

Pasteurization is the cleansing process through which each particle of a food or drink is

heated to a certain temperature for a specific amount of time. Throughout this process the

temperature of the product and time-length are closely monitored to prevent contamination.

Pasteurization is a process of heating water, usually liquid, to a

specific temperature for a definite length of time, and then cooling it immediately. This process slows microbial growth in water.

Pasteurization is not intended to destroy all pathogenic micro-organisms in the food or liquid. Instead, pasteurization aims to reduce the number of viable pathogens so they are unlikely to

cause disease (assuming pasteurization product is stored as indicated and consumed before its expiration date).

As water heats in a solar cooker, temperatures of 56° C and above start killing disease-

causing microbes. Water can be made safe to drink by heating it to this lower temperature only

66° C instead of 100° C (boiling) presents a real opportunity for addressing contaminated water

in developing countries.

To pasteurize water, heat it in the solar box to at least 65 degrees C (150 F) and keep the

water at that temperature or above for at least 30 minutes. If no thermometer is available, heat

until bubbles are rising from the bottom steadily. Natural waxes, such as beeswax, can be used to

indicate pasteurization temperature.

Solar conditions, weather conditions, latitude and box efficiency are all variables that affect

the ability of solar boxes to pasteurize water. As a general guideline, 4 liters of water can be

pasteurized in about 3 hours on a day with strong sunlight and the sun high in the sky. The

plastic- or glass-covered.

Purpose

The pathogens contained in water were discovered to transmit tuberculosis, scarlet fever,

diphtheria and a number of other diseases.

1. The first purpose of pasteurization is to kill these harmful pathogens to make water

safe for human consumption.

2. The second purpose of pasteurization is to extend the self-life of consumable water.

1.6 APPLICATIONS

The energy from the sun used to distill water is free. But the cost of building a still makes

the cost of the distilled water rather high, at least for large-scale uses such as agriculture and

flushing away wastes in industry and homes. Consequently, the solar still is used principally to

purify water for drinking and for some business, industry, laboratory, and green-house

applications. It also appears able to purify polluted water.

Solar distillation can be a cost-effective means of providing clean water for drinking,

cooking, washing, and bathing--four basic human needs.

It can improve health standards by removing impurities from questionable water supplies.

It can help extend the usage of existing fresh water in locations where the quality or

quantity of supply is deteriorating.

Where sea water is available, it can reduce a developing country's dependence on rainfall.

Solar stills, operating on sea or brackish water, can ensure supplies of water during a time

of drought.

Solar distillation generally uses less energy to purify water than other methods.

Solar distillation will permit settlement in sparsely-populated locations, thus relieving

population pressures in urban areas.

1.7 SCOPE OF WORK

We have study the how the solar still works and also it is practically possible or not. Also

we have calculates its efficiency. Solar still is to make water pasteurized by using the solar

radiation energy. The solar energy is non convectional energy which easily available

everywhere. In this chapter we are also analyze or evaluated its design by using the commercial

solar cooker convert in to the solar still.

CHAPTER 2: LITERATURE REVIEW

2.1 INTRODUCTION

This chapter is consist of Literature review of the box type solar still. Which gives a base

to present this work with reference to various research papers the study and ideology to design

the equipment is considered. The following Literature surveys focuses on the solar still but also

includes other renewable energy sources. The Solar still papers gives insight how far the field is

developed.

2.2 LITERATURE REVIEW

1. A.Mahesh, C.E. Sooriamoorthi, A.K.Kumaraguru,Department of Solar Energy, School of

Energy, Environment and Natural Resources, Madurai Kama raj University, (University with

Potential for Excellence) performed and experiment, that solar still is tested for the various input

water depths like 0.5,1.0,1.5,2.0,2.5,3.0 cm. And also the second experiment is conducted using

tap water, sea water, and dairy water’s samples were preheated at two different temperatures of

25 0C and 65 0C respectively.

From this experiment they concluded the tap water showed the maximum rate of

efficiency with a depth of 1.5cm compare to that of the other water depths.

And the other experiment with different preheated water samples, the tap water showed

the maximum efficiency compared to the other samples.

2. C.N.NATARAJ AND Dr. E.S. PRAKASH dept. of studies in mechanical engineering

university BDT College of engineering Davangere.

They performed that single basin double slope solar still and a similar one coupled with flat plate

collector to study the effect of augmentation on the still performance under local condition.

The purpose of this work is to evaluate the augmentation in productivity of the still. The

productivity of the still increases nearby 40% when it is coupled to flat plate collector.

3. Robert E. Foster, New Mexico State University, MSC 3 SOLAR, P.O. Box 30001Las Cruces, New Mexico, 88003-8001 USA

For the past decade, solar distillation has been introduced and applied as an option for household drinking water for several colonies communities along both sides of the U.S.-Mexico

border. Purifying water through distillation is a simple yet effective means of providing drinking water in a reliable and cost-effective manner. Solar stills effectively eliminate all water borne pathogens, salts, and heavy metals. Solar distillation produces an ultrapure water that is superior

to most commercial bottled water sources. Three organizations have been active in promoting the use and development of solar distillation on the Border, namely the El Paso So lar Energy

Association, New Mexico State University and Sol Aqua. Commercial still costs were halved over the

past decade due to manufacturing improvements. Over 200 Borderland families have adopted

cost-shared solar distillers to meet their drinking water needs. In addition, Sol Aqua has worked with Sandia National Laboratories with accelerated aging and other materials testing. This paper

discusses solar still performance and acceptance along the U.S. Mexico border. Clean drinking water remains one of the most important international health issues of

today, and solar energy offers important and effective solutions in meeting potable water needs

worldwide. Low cost solar stills offer an immediate and effective solution in reliably providing safe drinking water year after year. Single-basin solar stills are easy to build, inexpensive and

extremely effective in distilling water with a high total dissolved salt content and in killing bacteria such as cholera and E. Coli. Single basic solar stills can use commonly available equipment, based on proven solar still designs. Average water production is about 0.8 liters per

square meter per sun hour. Solar stills can bring immediate benefits to their users by alleviating chronic problems caused by water-borne diseases.

Solar stills offer the only realistic and cost-effective means to provide safe drinking for many Borderland colonias residents who have few other realistic and affordable options available. Likewise, solar stills have tremendous potential worldwide in economically addressing

rural potable water needs and in saving lives. The Borderlands solar distillation water purification projects have been an overall success. This 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. As Border water supplies grow

increasingly scarce and more difficult to purify (i.e. increasing salinity), solar distillation offers a practical, effective, and relatively inexpensive means for residents to purify their drinking water. It can be practically applied on a decentralized and immediate basis by any end-user around the

globe.

2.3 CONCLUDING REMARK

1.The tap water shows maximum efficiency at a height of 1.5cm to 2.5cm & with different

preheated water samples, the tap water showed the maximum efficiency.

2.Solar still productivity increases about 40% when coupled to flat plate collector and also

production rate decreases with increasing water depth.

3.Single basin solar stills are easy to build inexpensive with a high total dissolved salt content

and in killing bacteria. Solar stills have tremendous potential world in economically addressing

rural portable water needs & in saving lives.

CHAPTER 3: THEORITICAL ANALYSIS OF BOX TYPE SOLAR STILL (BTSS)

3.1 INTORDUCTION

Analysis of solar still is most important topic of our project. There are lots of pasteurizer are

available in market for purification of water. The cost is high and it require conventional energy.

The use of solar energy for pasteurizes water. This chapter contains theoretical analysis of BTSS.

The various components are identified and analyze theoretically with relevant references.

Components use in solar still –

Major components:

Basin.

Support structure.

Double glass Transparent Top cover.

Storage tank

Ancillary components:

Insulation (usually under the still)

Sealants

Piping and valves

Temperature Indicator

An external cover

Reflector

3.2 SIMPLE THERMAL ANALYSIS OF BTSS

From the First Law of Thermodynamics, you know that the amount of energy exiting a

system can never be greater than the amount of energy entering a system. The heat load can be

conservatively estimated to be equal to the amount of electricity consumed if electricity is the

only form of energy entering a system.

During pasteurization heat gain water by solar irradiation:

Q = m x Cp x ΔT ….. (3.1)

Conduction

In general, the rate of conductive heat transfer is given by: Qcond = K(∆𝑇/∆𝑋) ….. (3.2)

Convection

Qconv = U A (T0 - Tin) ….. (3.3)

Radiation

In general, the rate of radiation heat transfer from the top surface and sky given by:

Qrad = σ .A.F1-2(Ts4 - Tsky

4 ) ….. (3.4)

Where Tsky = Temperature of sky= 0 K, F1-2=1

3.2.1 FREE CONVECTION IN THE BTSS

Free convection can form the dominant mechanism of heat loss in a solar thermal device and

therefore it is the key item limiting the collectors efficiency.

In case of parallel layer of stationary fluid of thickness L and having a temperature Th on one

face and Tc on the other (refer fig.3.1) Th being greater than Tc, the heat flux q (i.e. heat flow rate

per unit area) is given by eq. (3.1)

q = kf (Th– Tc) / L ….. (3.5)

Fig. 3.1: Horizontal fluid layer (θ = 0)

Nusselt Number

To calculate the heat transfer across and inside the double glass layer by convection , a

dimensionless number called the Nusselt number(Nu.) is introduced.

qa= ha (Th – Tc)

therefore ha = qa/(Th – Tc) represent the corresponding heat transfer coefficient

then Nusselt Number is defined by following equation.

Nu = ha L / k ….. (3.6)

Nu represents the ratio of the heat across the fluid layer in the convection situation compared to

that in the purely conducting situation.

Rayleigh Number

It is evaluated at a mean temperature, Tm, its defined as

Tm = (Th + Tc) / 2

= 1/Tm

The Rayleigh Number Ra, and the prandtl number Pr. They are defined by following equation

Ra = {g. . ( Th – Tc ) L3 }/∝.ν ….. (3.7)

Prandalt number

Pr= Cp ./K ….. (3.8)

Where ∆T = Th – Tc. When Pr. Number it is restricted to gases, then its value varies very

less , so dependence of Nu on Pr is, very slight ,so that Prandtl number effect can be ignored for

gases. The calculation for Pr. Will be ignored for double glass cover.

The Horizontal Layer of air between double layer glass cover

The horizontal layer as sketched in fig.3.2 is a represents the layer found in BTSS. When

it is found stationary the Nu= 1

At Rayleigh Number slightly greater than 1708, an instability in the stationary state result in the

formation of cellular motion in the fluid. The experimentally measured Nu-Ra relationship(fig.

3.2) for air .

Nu = 1 + 1.44 [1 – 1708/Ra ]* + [ ( Ra/5380) 1/3 – 1] * ….. (3.9)

where a square bracket having subscript dot indicate that if the argument inside the brackets is

negative, the total quantity is taken as zero, otherwise the brackets behave normally.

2

20

40

1

4

6

8 10

8

10 3 4

10 5 10 6 10 7 10 8 10

Nu

Fig.3.2: The experimentally measured Nu-Ra relationship for with (θ = 0)

3.2.2 COMBINED FREE CONVECTION AND RADIATION COEFFICIENTS ACROSS

AIR LAYERS

Air Layers between two glass of cover and between water surface and bottom glass of cover

Heat transfer across parallel air layer takes place in the BTSS by two mechanisms. Namely free

convection and thermal radiation. It is described in table No.

Table No 3.1. Radiation and convection heat flow in BTSS

Particular Description

Convection 1. The convection heat transfer above the surface of top cover.

2. Convection heat transfer between the two glass cover, which is minimize by

considering Rayleigh No. upto 1708.

3.The convection heat transfer above the surface of water it is to be minimized,

but the glass cover is air tight than it is considered that air is stagnant hence

convection is negligible.

Solar Radiation 1. It is transmitted through the covers towards the absorber tray, and the

thermal radiation arising from the emission of radiation by basin.

2. Long wave radiation emits from tray surfaces at a lower temperature than

sun when no water is present. The long wave radiations do not cross the double

glass cover. This is also called green house effect.

3. When water is present in the still then the heat transfer due to radiation from

the basin is minimum can be neglected.

4. When after is present the heat transfer due to radiation from the water

surface to fluid layer-1.

5. The solar radiations incident on the Top glass cover a part of it will be

reflected and remaining will be transmitted inside the still and absorbed by the

glass .

In actual the net long wave radiant exchange of heat across the air gap between basin and cover

hence it is to be expressed as heat is given by eq. (3.7)

q r = { σ . (Th4

– Tc4 )}/ (1 /Є h + 1 / Є c - 1 ) ..(3.10)

The quantity 1 / (1 /Є h + 1 / Є c - 1 ) termed as effective emissivity of the body.

The radiant heat transfer coefficient can be defined as work done for convective heat transfer

coefficient. Hence, h r = qr / ( Th - Tc )

h r = { σ . (Th4

– Tc4 )}/ {(1 /Є h + 1 / Є c - 1 ) ( Th - Tc )} ….. (3.11)

Total hea t flux ava ilab le a t bo ttom surface o f bo ttomglass o f cover

qT = qa + qr = ha ΔT + hr ΔT ….. (3.12)

Heat Loss from the top cover

heat loss is the important and major loss in a BTSS. The variables determining the

upward heat flux are.

i. Temperature of the absorber (Basin).

ii. Temperature of the outer air and sky.

iii. Number of glass covers and spacing.

iv. Tilt of glass plates from the horizontal.

v. Wind velocity over the top cover.

The first four are important in all cases while the wind velocity assumes importance when

the solar thermal device consists of a single glass cover.

Assumptions

The steady state unidirectional heat flow from Top cover, backs and sides of BTSS.

Heat Flow Mechanism: The loss from basin to the first glass cover is by radiation and

convection. No radiant heat is transmitted through the glass as glass is opaque to long wave

radiation

The Basin temperature do not exceed 150oC to 175oC. when no water is present.

The basin temperature donot exceed 90 oC to 95 oC when water is present.

The same quantity of heat is transferred through the upper face of the bottom cover to the

lower face of the top glass cover by radiation and convection.

Consider thermal resistance within glass plate/cover is negligible compared with plate-to-plate

resistance.

The mean temperature may be assigned to each glass plate.

Since the air is diathermic to radiation, the loss of heat by convection from a basin to an air space

equals the loss by convection from air space to next bottom plate of cover. The convection loss

from glass plate to next glass plate by air gap between two glasses of cover to out site air . The

schematic diagram of a BTSS is shown in fig.3.4.

Fig.3.3: Schematic diagram of box type solar still (BTSS)

The heat flux qa by convection for fluid layer-1 is given by eq. (3.13)

qa1 = hal (Thl – Tcl) ….. (3.13)

and the radiation heat flux qr for fluid layer - 1 is given by eq. (3.14)

qr1 = {σ . (Th 14

- Tc 14 ) }/ (1 /Є h 1 + 1 / Є c 1 - 1 ) ….. (3.14)

Total heat loss from the fluid layer-1 is given by qTl = qal + qrl

Radiative heat transfer coefficient in fluid layer-1

hr 1 = {σ . (Th 12

+ Tc 12 ) (Th 1 + Tc 1 )}/ (1 /Є h 1 + 1 / Є c 1 - 1) ….. (3.15)

The same heat flux occurs from first glass cover to the second glass cover and so for

fluid layer – 2. Under steady state qT1 = qT2.

qa2 = ha2 (Th2 – Tc2) ….. (3.16)

qr2 = {σ . (Th 24

- Tc 24 )}/ (2 /Є g l a s s - 1) ….. (3.17)

The total heat losses from the second fluid layer-2 is qT2 = qa2 + qr2

Heat transfer coefficient in fluid layer-2

hr2 = {σ . (Th 22

+ Tc 22 ) (Th 2 + Tc 2 )} / (2 /Є g l a s s - 1) ….. (3.18)

The radiant interchange between the top cover and the sky

qr3 = . Є g l a s s (Tt4 – Tsky

4 ) ….. (3.19)

Tsky = 0.0552 Ta3/2 ….. (3.20)

Tt = Top cover temperature

Heat transfer coefficient between top cover and and the sky

hr3 = Є g l a s s . . (Tt4 – Tsky

4) / ( Tt - Tsky ) ….. (3.21)

Heat carried away by the ambient air at a temperature Ta moving with a velocity Vw from the

upper surface of the top cover which is at a temperature Tt the heat transfer coefficient to the

wind speed.

hw = 5.7+3.8 Vw ….. ( 3.22)

Rear Losses

The heat lost by conduction from back and side

q b or s = ki ( Th1 - Ta ) / δ i ….. (3.23)

h b & s= ki / δi ….. (3.24)

Radiation heat transfer coefficient from honeycomb walls can be calculated from eq. (3.25)

hr2 = [1 / (1 /Є h 2 + 1 / Є c 2 + {Є wr (A.R) + 1}] . { (Th2

4 – Tc24)}/ (Th2 – Tc2) …..(3.26)

A.R.= Aspect ratio (L/w), r = Constant (equal to 1 for glass)

3.2.3 THERMAL NETWORK OF BTSS

The thermal network for a solar still with a double glass cover is shown in fig.3.4. The

tray absorbs solar Energy. This absorbed energy is distributed to losses through top, bottom and

edges and to useful energy gain. The overall heat transfer helps to co nvert thermal network

shown in fig.3.4(a) to the equivalent thermal network of fig.3.4 (b)

Fig. 3.4 : Thermal network of box type solar still (BTSS).

The breakdown of heat losses in solar still are as follows:

Table 3.2 Heat losses in box type solar still

Type of losses Percentage

Edge 1 – 3

Back 5 – 10

Radiation 5 – 7

Convection 25 – 30

Heat losses in solar still

Heat losses in solar still based on thermal network are given in table 3.2.

Table 3.3 formulae obtained from thermal network for heat losses

Description Formula

Upward heat loss

Basin to 1st Glazing , convection and radiation losses

through fluid layer-1

Convection and radiation losses through fluid layer-2

Heat loss from the top surface due to radiation and

wind velocity

R1 = 1 / (ha1 + hr1)

R2 = 1 / (ha2 + hr2)

R3=1/hw+hr3

Rear heat loss through insulation

Back loss

Side loss

R4 = 1 = δ i

hb ki

R5 = 1 = δ i

hs ki

Heat loss coefficients

The top loss coefficient from the cooker absorber

The back loss coefficient

The side loss coefficient

The overall heat loss coefficient

Ut = 1 / ( R1+R2+ R3 )

Ub = 1/R4

Us = 1/R5

UL = Ut + Ub + Us

3.2.4 Effect of different color in solar still

We are using apoxy black coated material in solar still because of its radiation absorption capacity is higher than all other colour so its increase efficiency of

solar still. and give better result in less time.

Table No 3.4. Description of surfaces with Absorptivity and Radiation

Sr.No Surface Solar Radiation Absorption(α)

Low Temperature

Radiation at 25oC

1 Polished alluminium 0.15 0.06

2 White 0.14 0.97

3 Yellow 0.30 0.95

4 Cream 0.25 0.95

5 Light gray, green blue 0.50 0.87

6 Mid. Gray, green blue 0.75 0.95

7 Dark gray, green blue 0.95 0.95

8 Black 0.97 0.96

Fig. 3.5 : Diagram of Solar Load Vs Temperature rise

3.2.6 STORAGE TANK

The design of storage tank is depend upon the capacity of BTSS. And the cooling of hot water is

through conduction and convection process.

The heat transfer is given by the basic equation,

Qtotal = mcp ΔT ….. ( 3.27)

Mass of water is depend upon by the capacity of the box type solar still. And also the decide

specific heat for water.

In storage tank the upper surface of water is cooled by the natural convection and the side and

bottom part of tank is cooled by the conduction process.

The heat transfer through conduction is given by the basic equation for conduction process.

Qcond =(K x Acond x ΔT)/L ….. ( 3.28)

The thermal conductivity (K) is depends upon which material we are selected for conduction

process.

The heat transfer through convection in storage tank is given by the basic equation for

convection process

Qconv = hw x Aconv x ΔT ….. (3.29)

Heat carried away by the ambient air at a temperature Ta moving with a velocity Vw from the

upper surface of the top cover which is at a temperature Tt, the heat transfer coefficient of convection to the wind speed.

hw = 5.7+3.8 Vw ….. (3.30)

The wind velocity of the air (Vw) is decided by the weather analysis chart as per the location of

particular city.

The total heat transfer through the storage tank is given by

Qtotal = Qcond. + Qconv. ….. (3.31)

Using the eqn. calculate the area of the conduction by using the relation below,

Here we are considering the storage tank top surface area is vary between 17% to 40% for the

cooling through natural convection and the remaining part of the storage tank is cooling through

conduction.

Qcond. = 0.6 X Qtotal ….. (3.32)

Qconv. = 0.4 X Qtotal ….. (3.33)

Using above value of convection and conduction find the area of that particular conduction

(Acond) and convection (Aconv) process eqn. (3.28,3.29),

As=Aconv + Acond ..… (3.34)

Now, eqn. (3.39) calculate the surface area required for the cooling of hot water through

conduction and natural convection.

3.2.7 CHARACTERISTICS OF WATER

Density is a measure of how compact a substance is. It is defined as the mass of a

substance divided by its volume. Solids are almost always the most dense form of a substance,

then liquids and then gases. As temperature increases, the density generally decreases. Pure

water is an exception to this and is the only substance which has its highest density as a

liquid. Water is at its most dense at about 4 oC. This is because hydrogen bonds between water

molecules give ice a very stable open ordered structure. At low temperatures, water has a

higher density than ice and this means that ice floats.

Fig.No.3.6: Variation of water density vs Temperature.

Table No.3.5 CHARACTERISTICS OF DRINKING WATER SUPPLIED .

Parameter

Average Results Drinking water

Permissible Limit

BIS:10500-1991

Colour Slightly whitish 25 Units

Odour Chlorinous Unobjectionable

Turbidity (NTU) 7 10

Total Dissolved Solids (mg/L) 385 2000

Total Hardness (mg/L) ( as CaCO3 ) 114 600

Calcium (mg/L) (as Ca) 26 200

Magnesium (mg/L) (as Mg) 12 -

Chloride (mg/L) (as Cl ) 109 1000

Sulphate (mg/L) (as SO4 ) 54 400

Ammoniacal Nitrogen (mg/L) (as N ) 0.07 -

Albuminoid Nitrogen (mg/L) (as N ) 0.30 -

Nitrite (mg/L) (as N ) Nil -

Nitrate (mg/L) (as NO3 ) Nil 100

Phenolphthalein Alkalinity (mg/L) ( as CaCO3 ) Nil -

Total Alkalinity (mg/L) ( as CaCO3 ) 62 600

Phosphates (mg/L) (as PO4 ) 0.015 -

Iron (mg/L) (as Fe ) 0.10 1.0

PH 7.1 6.5 - 8.5

Silicates (mg/L) (as SiO2 ) 10 -

Fluoride (mg/L) (as F ) 0.10 1.5

Specific conductance (micro mhos/cm) 595 -

3.3 CONCLUSION

The present chapter has outlined the development of the model used to simulate the box

type solar still operation. Here we calculate the thermal effect which is occurs during

process. By thermal analysis we conclude that water can be pasturised at minimum cost and

minimum time.

CHAPTER 4 : EXPERIMENTAL SETUP AND PLANNING OF EXPERIMENT

4.1 INTRODUCTION

In this chapter, we have arranged the full experiment set-up, which is appropriate to the solar still system work easily. Also the work to be carried out by the experimental set-up is

properly or not. Here the decide the full experiment procedure and proce ss planning for our project. And through full arrangement of the experimental set-up to full- fill the result which is to

be achieved. So this chapter is also useful for our project work. 4.2 EXPERIMENTAL SET-UP

Fig. 4.1: Experimental Set-up of BTSS

Experimental work to be carried out

A standard commercial Box Type Solar Still with the following specification was used:

Capacity: 20 litres Effectiveness factor: 80 % Power consumption: Through Solar Energy

Dimensions: (400mm x 436mm x 125mm)

Experiment procedures

The procedures will be as follows:

a) Water inlet in box type solar still’s basin, thermometer is placed in for temperature

measurement.

b) Water will be heated at 80 0C to 90 0C by solar energy. c) Then this water will be drawn to the storage tank through pipe, in the storage tank water will

be cooled by natural convection.

d) Here in storage tank the water will be cooled and temperature will be reached at 35 0C e) The filter is provided at the outlet of storage tank which removes dust particals from water.

f) Then filtered water is brought to earthen pot through pipe for further normal cooling of water.

g) Here in earthen pot water temperature reach at 27 0C to 30 0C.

Results to be achieved

The pasteurised drinkable water will be obtained at effectiveness of greater than 80% of solar still.

4.3 MATERIAL SELECTION

Sr. No. Name of the parts Material Quantity

1. Solar Cooker Alluminium 1

2. Steel Tank Steel 1

3. Flexible Pipe PVC 2mtr

4. ½”Elbow PVC 2

5. ½”Tee PVC 2

6. ½”Washer PVC 2

7. ½”Valve PVC 1

8. Bush PVC 2

9. ¾”Angle Mild Steel 14 Kg.

10. N.C.Paint - 500ml

11. Thinner - 500ml

4.4 REQUIREMENT OF M/C TOOLS AND MEASURING EQUIPMENTS

Requirment of Machine Tools

Hacksaw Machine

Welding Machine

Soldering Machine

Drilling Machine

Requirment of Different Equipments

Hacksaw Blede

Cutting Tools

Welding Rod

Hammer

Sizzer

File

Measuring Instruments

Thermometer

Measuring Tap

Shrinkage Rule

CHAPTER 5 : COSTING

5.1 INTORDUCTON

It is the determination of actual cost of article after adding different expensive incurring

in various departments. It may also be definite as a system which systematically. Record and the

expenditure included in the various departments.

To determine any the cost of manufacture product.

5.2 AIM OF COSTING

The important aim and object of costing are as follows:

1. To determine the cost of each article.

2. To determine the cost of each article operation to keep central over head expenses’.

3. To supply information for costing of wastage.

4. It helps in reducing the total cost of manufacture.

5.3 PURCHASE MATERIAL AND LABOUR COST

Sr.

No.

Name of Parts and Materials Rate Quantity Total Rupees

1. Solar Cooker 3500/piece 1 3500

2. Glass 140/piece 2 280

3. Wooden Frame 180/piece 1 180

4. Stainless Steel Sheet 300/kg 2kg 600

5. NC Black Coating 225/Lt 400ml 90

6. Brush 12/piece 1 12

7. Thinner 70/Lt 500ml 35

8. Galvanised Sheet 45/kg 3.5kg 158

9. Earthen Pot 65/piece 1 65

10. M.S.Angle 40/kg 13.5kg 540

11. All PVC Fittings - - 275

TOTAL 5735

5.3 FINAL COST OF BTSS

PRIME COST

= Total cost of purchase material and part + Labor cost

= 5735 + 755

=6490 Rs.

SALES AND DISTRIBUTION OVERHEAD COST

= 10% of Prime Cost

= 649 Rs.

TOTAL COST OF BTSS

= Prime cost + Sales and Distribution Overhead Cost

= 7139 Rs.

PROFIT

= 10% of Total Cost

= 714 Rs.

SALING PRICE

= Total Cost + Profit

= 7850 Rs.

CHAPTER 6 : RESULTS AND DISCUSSION

2.1 INTRODUCTION

2.2 RESULTS AND DISCUSSION

CHAPTER 7: CONCLUSION

7.1 FUTURE SCOPE OF WORK

The solar energy is non convectional energy which easily available everywhere.

So its an environmental friendly product. In this chapter we are also analyze or evaluated its

design by using the commercial solar cooker convert in to the solar still.

The solar still is using water to in drinkable form and also pasteurized water. In

future we have using these solar still to get the distilled water. Also its make water to in

drinkable form.

In future the solar still is give a different impression in big industries and special

occasions.

7.2 CONCLUSION

We have given detail explation of our project. We finally conclude that our project is

completed in a given time limit with satisfaction. While doing this project we learn about various

engineering fields helps each other to make different kind of work easily. We visited various

industries, work shop and engineering shop. We also know about cost of various materials,

which we required. We learn the group works from this project, which is important for our future

industrial life and how to manage with different skill persons and how to work different

condition without loosing more time, how we can give our best work to our project/industrial

life.

Finally we are very thankful all group members and our all the mechanical department

professors and H.O.D. and also our class collogues, which directly of indirectly help us to

complete this project on time.

APPENDIX- I

Sample Calculations:

Performance evaluation of Box Type Solar Still

Table 1. Radiation properties of some surface coatings and materials used in solar still.

Sl.

No. Description

Solar Energy

Absorptance α

Long waves Radiation

admittance Є

1. Black Enamel Paint 0.83 0.83

2. Lamp Black 0.95 0.95

3. Sol chrome (Black chrome on nickel

plated copper Substrate)

0.965 0.15

4. Lamp Black in Epoxy 0.96 0.89

5. Selective Paint 0.94-0.96 0.35-0.45

6. Aluminium 0.09-0.1 0.102-0.113

7. Parsons Black Point 0.98 0.981

Table 2. Physical and optical properties of some glazing materials available in India

Sl. No. Description Thermal Conductivity (K)

W /m K Transmittance

1. Glass 0.640 - 0.7443 ---

2. Safex (4mm) 0.84-0.88

3. Atul (5mm) 0.80-0.84

4. Vallabh Glass 0.80-0.85

Fig .1

Fig2

Below Table shows break down of Heat losses in solar cookers

Type of losses Percentage

Edge 1 – 3

Back 5 – 10

Radiation 5 – 7

Convection 25 - 30

THERMAL NETWORK OF BOX TYPE SOLAR STILL

The thermal network for a Box type solar still with a double glass cover is shown in fig.

The tray absorbs solar Energy. This absorbed energy is distributed to losses through top, bottom

and edges and to useful energy gain. The overall heat transfer helps to convert thermal network

shown in fig.(1) to the equivalent thermal network of fig.(2)

Heat Transfer Calculations For Fluid Layer-1

Data used for calculation as given below:

Th1 = 75oC and Tc1 = 65oC

Tm = ( Th1 + Tc1 ) = {(75 + 273 )+ (65 + 273 ) }/ 2 = 343 K or 70oC

Properties of air at a mean temperature of 70oC

Kinematic Viscosity, ν = 20.21 x 10-6 m2/sec.

Thermal diffusivity, = 2.891 x 10-5 m2/sec

Coefficient of Volumetric expansion, β = 2.91 x 10-3 / K

g = 9.81 m/sec2 , characteristic depth L 1 =0.80 m,

Thermal conductivity of air, kf = 29.48 x 10-3 W/m K

The aperture area of glass cover, A = .436 x .436 = 0.190096m2

Є h 1 = 0.89 (refer table for Lamp Black in Epoxy)

Є c 1 =0 .85 ( refer table for Vallabh glass)

Ra = {g ( Th1 – Tc1 ) L3 }/ .ν

Ra = 2.5 x 108

Nu = 1 + 1.44 [1 – 1708/Ra ]* + [ ( Ra/5380) 1/3 – 1] *

Nu = 37.39

Nu = ha1 L1 / kf

ha1 = 1.38W/m2 K

qa1 = ha1 (( Th1 - Tc1 ) = 1.38. ( 75 + 273) - (65 + 273) =13.8 W/m2

Qa1 = qa1 x At = 13.8 x 0.190096m2 = 2.62 W

qr1 = σ . (Th 14

- Tc 14 ) / ( 1 / Є h 1 + 1 / Є c 1 - 1 )

qr1 = 70.41 W/m2

Qrl = q r 1 x Area = 70.41 x 0.190096 m2 = 13.38 W

Radiation heat transfer coefficient hrl

hr 1 = {σ . (Th 12

+ Tc 12 ) (Th 1 + Tc 1 )} / (1 /Є h 1 + 1 / Є c 1 - 1)

h r 1 = 7.04 W/m2K

Total heat Supplied to Cooker Cover through fluid layer -1

Q1 = Qal + Qrl = 2.62 W + 13.38 W = 16 W

Heat Transfer Calculations for Fluid Layer – 2

Data used for calculation as given below:

Q1 = 16 W

Thermal conductivity of glass k = 0.7443 W/m K (refer table )

Thickness of cover glass t = .003 m, L2 = 0.0125 m.

The aperture area of glass cover A = .436 x .436 = 0.190096m2

Є g l a s s = 0.85 ( refer table for Vallabh glass)

The heat transferred due to conduction

Qc = {k.A (Tcl – Th2)} / L = Q1 =16 W

(Tcl – Th2) = Qc .L / k.A = ( 16x 0.003 ) / ( 0.7443 x .0190096) = 33 oC (take 1 oC)

Tcl = 338 K. Th2 = 338 – 1 = 337 K

Similarly Tt - Tc2 = 1oC or K. Taking the maximum value of Tt observed

Tt = 40 oC = 313 K,

Tc2 = Tt – 1 k = 313 – 1 = 312 K

The mean temperature therefore for fluid layer-2 is equal to

Tm = (337 + 312) / 2 = 324.5K or 51.5 oC (take 54oC)

The air properties at a mean temperature of 54oC as follows

Kinematic viscosity, ν = 18.61 x 10-6 m2/sec.

Thermal diffusivity, = 2.65 x 10-5 m2/sec.

Coefficient of volumetric expansion, β = 3.06 x 10-3/ K.

Taking the thermal conductivity of air, K=28.3 x 10-3 W/m K

g = 9.81 m/sec2 , characteristic depth L 2 =0.0125 m .

(Th2 – Tc2 ) = (337– 312) = 25 K

Ra = {g (Th2 – Tc2 ) L3 }/ .ν

Ra = 2973

Nu = 1 + 1.44 [1 – 1708/Ra]* + [ ( Ra/5380) 1/3 – 1] *

Nu = 1.43

Nu = ha2. L2 / kf

ha2 = 3.23 W/m2 K

qa2 = ha2 x ( Th2 – Tc2 ) = 80.75 W/m2

Qa2 = qa2 x A = 15.35 W

qr2 = {σ . (Th 24

- Tc 24 )}/ (2 /Є g l a s s - 1)

qr2 = 143.41 W/m2

hr2 = {σ . (Th 22

+ Tc 22 ) (Th 2 + Tc 2 )} / (2 /Є g l a s s - 1)

hr2 = 5.74 W/m2 K

Qr2 = qr2 x A2 where A2 = 0.190096 m2

Qr2 = 27.26 W

Total Heat transfer from fluid layer-2

Q2 = Qa2 + Qr2 = 15.35 + 27.26 = 42.62 W

Heat transfer between top cover and sky

Data used for calculation as given below:

The aperture area of glass cover A = .436 x .436 = 0.190096m2

Average wind velocity Vw =8 kmph as per the weather analysis chart

Є g l a s s = 0.85 ( refer table for Vallabh glass)

Tt = 313 K

Ta = 303 K

Tsky = 0.0552 Ta3/2 = 291.14 K

hr3 = Є g l a s s . (Tt4 – Tsky

4) / ( Tt - Tsky )

hr3 = 0.85 x 5.67 x 10-8 x {(313) 4 – (291.14) 4}/ (313 – 291.14) = 5.26 W/m2 K.

hw = 5.7+3.8 Vw W/m2K = 14.14 W/m2 K.

Back and side losses from tray

Thermal conductivity of insulation (glass wool), k = 0.0372 W/m K

Thickness of back δi b = 52 mm

Thickness of side δi s = 74 mm

Area of the back, A b = 400mm x 400mm = 0.16 m2

Area of each side, A s = 0.08 x (0.436 + 0.400) /2 = 0.03344 m2

Th1 = 348 K and Tcasing = Ta = 303 K

h b (back) = ki / δi b = 0.0372 / .052 = 0.715 W/m2 K

q b (back) = h b x ( Th1- Ta ) =32.18 W/m2

Q b (back) = q b x A b = 5.15 W

h s (side) = ki / δi s = 0.0372 / 0.074 = 0.503 W/m2K

q s (side)= h s x ( Th1- Ta ) = 0.503 ( 348 – 303) = 22.64 W/m2

Q s (side) = q s x A s x 4 = 3.03 W (four sides)

Total heat loss from the back and sides

QL(back and side) = Q b (back) + Q s (sides) = 5.15 + 3.03 = 8.18 W

Overall heat loss coefficient of solar still

Thermal Resistances

R1 = 1 / (ha1 + hr1) = 0.1188 m2 K/W

R2 = 1 / (ha2 + hr2) = 0.1115 m2 K/W

R3=1/ (hw+hr3) = 0.0515 m2K/W

R4 = 1 / hb = δ i b / ki = 1.4 m2K/W

R5 = 1 / h s = δ i s / ki = 2 m2 K/W

Overall Heat Loss Coefficient

Ut = 1 / (R1+R2+ R3) = 3.5 W/m2 K.

Ub = 1/R4 = 0.71 W/m2 K.

Us = 1/R5 = 0.50 W/m2 K

UL = Ut + Ub + Us

UL = 4.71 W/m2 K.

QL = Q2 + QL(back and side) = 50.8 W

REFERENCES

1. ↑ Heat transfer. (2010, April 15). In Wikipedia, the Free Encyclopedia. Retrieved 15:56, April 22, 2010, from

http://en.wikipedia.org/w/index.php?title=Heat_transfer&oldid=356169993

2. ↑ Convection. (2010, April 22). In Wikipedia, the Free Encyclopedia. Retrieved 16:31, April 22, 2010, from

http://en.wikipedia.org/w/index.php?title=Convection&oldid=357620678 3. ↑ Conduction (heat). (2010, April 21). In Wikipedia, the Free Encyclopedia. Retrieved

16:14, April 22, 2010, from http://en.wikipedia.org/w/index.php?title=Conduction_(heat)&oldid=357403462

4. ↑ Thermal radiation. (2010, April 12). In Wikipedia, the Free Encyclopedia. Retrieved

16:18, April 22, 2010, from http://en.wikipedia.org/w/index.php?title=Thermal_radiation&oldid=355601161

5. Pr. Kaabi Abdenacer, Smakdji Nafila, 2007, Impact of temperature difference (water-

solar collector) on solar-still global efficiency, Desalination, Volume 209, Pages 298-305.

6. K. Kalidasa Murugavel, Kn.K.S.K. Chockalingam, K. Srithar, 2008, An experimental

study on single basin double slope simulation solar still with thin layer of water in the

basin, Desalination, Volume 220, Pages 687-693.

7. Bilal A. Akash, Mousa S. Mohsen, Omar Osta and Yaser Elayan, 1998, Experimental evaluation of a single-basin solar still using different absorbing materials, Renewable

Energy, Volume 14, Issues 1-4, 8. Robert E. Foster New Mexico state university, Ten Years of Solar Distillation

Application Along The u.s-mexico.

9. A.Mahesh, C.E. Sooriamoorthi, A.K.Kumaraguru,Department of Solar Energy,School of Energy, Environment and Natural Resources,Madurai Kamaraj University,Design construction and performance evaluation of low cost basin type solar still.

10. C.N.NATARAJ AND Dr. E.S. PRAKASH dept. of studies in mechanical engineering university BDT College of engineering Davangere., Experimental Study of Single basin

solar still coupled with flat plate collector. 11. Engineering heat and mass transfer by M.M.Rathore ch-2,7,12