Annual performance of solar stills for different inclination of condensing covers and water depths.

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ANNUAL PERFORMANCE OF SOLAR STILLS FOR DIFFERENT INCLINATIONS OF CONDENSING

COVERS AND WATER DEPTHS

by

ANIL KUMAR TIWARI Centre for Energy Studies

submitted

in fulfilment of the requirements of the degree of Doctor of Philosophy to the

Indian Institute of Technology, Delhi

JULY, 2006

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C ertiffic ate

This is to certify that this thesis entitled "Annual performance of solar stills for different inclinations of condensing covers and water depths"

being submitted by Anul Kumar Tiwari to the Indian Institute of Technology Delhi, is worthy of consideration for the award of the degree of Doctor of Philosophy and is a record of bonaffide research work carried out by him. He has worked under my guidance and supervision and has fuiffihled the requirements, which to my knowledge have reached the requisite standard for the submission of this thesis. The results contained in this thesis have not been submitted in part or full to any other University or Institute for the award of any degree or diploma.

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Dated: July 14, 2006

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Centre for Energy Studies

Indian Institute ofTechnology Delhi New Delhi-i i0016

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Acknowledgements

First of all, I express my thanks and deep gratitude to the omnipresent almighty God by whose grace my dream of completing this thesis has come true.

With all due regards, I would like to express my deep sense of gratitude, indebtedness, and thankfulness to my Supervisor and Guide Professor (Dr.) G.N.Tiwari, who has always shown me the right path and without whose guidance, I would have not done any thing during my research work. He has shown an admirable patience and fortitude in guiding me during my research period. I always found him utmost cooperative and helpful during all the stages of my research tenure. I, without any doubt in my mind, consider myself most fortunate to work under Professor Tiwari's guidance. I heartily thank the almighty God to give me an opportunity to work under Professor Tiwari's able guidance. I shall always remain grateful to my supervisor for his father-like behavior and guidance.

Fortunately, I have become a part of Solar Distillation Group that has started working way back under the dynamic leadership of Professor M. S . Sodha, who has done quite remarkable work in the fleld of Solar Distillation together with my supervisor Professor G.N.Tiwari. Even today, many scholars have been able to fulfil their dreams because of his able direction. I pray to God for their long, prosperous and healthy life.

I am very much thankful to Prof. M.K.G. Babu, Head of Department CES, Prof. A. Chandra, Prof. T. S. Bhatti and Dr. Subodh Kumar ofCentre for Energy Studies for their constant support and encouragement. My sincere thanks go to Prof.

v. K. Srivastava, Ex-Dean IRD for his academic discussion and encouragement.

Prof. J.P. Subrahmanyam, Mech. Engineering has helped me by providing moral support through his words and exclusive emails time to time. In fact, he has been very helpful to me throughout my research work. I am very much thankful to him for his kind support extended since the days of my M.Tech.

I am deeply indebted to Dr. Rajesh Tripathi, Dr. Anuj Kumar Sharma and Mr. Vishal Singh for their encouragement and all possible helps extended to me to complete this daunting task of research work.

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I am highly grateful to Secretary, Department of Technical Education Ministry, Government of Chhattisgarh to be kind enough for sponsoring me under quality improvement programme (QIP). I am also very thankful to Dr. Rajesh Pathak and Dr. D. G. Motwani of Directorate, Technical Education, Chhattisgarh to help me for getting the sponsorship and relieving. In particular I am thankful to Dr. R. P.

Sukhija, Dr. D. K. Mishra, Mr. Debashis Sanyal and Dr. Anupam Shukia, NIT Raipur for their cooperation extended in getting the sponsorship and relieving fflom the Government of Chhattisgarh.

My special thanks go to my colleague and ffliend Prof. A. M. Rawani, Mechanical Engineering at National Institute of Technology, Raipur for extending all possible support for the works related to my department at NIT Raipur.

I would like to thank the coordinator QIP, lIT Delhi and his offfice as a whole for extending all supports; particularly my sincere thanks go to Ms Sheela Koli of QIP offfice for extending her generous support during my stay at IlT Delhi. I also like to express my regards to Mr. La

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mi Chand and Mr. Dhanne Singh for providing me all intense support in the lab and outside. I am very much thankful to Mr. Umesh Mishra for the help he extended during my rigorous experimentation that lasted for a year.

I would like to express my thankfulness and obligation towards my colleagues Ashish Shukla, Dr. Arvind Tiwari, Bikas Sarkar and Anand Joshi for providing me with a lovely company during my stay in the group.

I have no befitting words to express deep sentiments towards my wife; Smt. Vandana Tiwari, Sons; Abheesht and Kushagra for their whole hearted Support and patience during the period ofmy stu

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Finally, this acknowledgement would prove to be meaningless if I do not express my deep sense of regard and gratefulness to my brother-in-law Dr. Dinesh Upadhyaya, nephrologist, Arogya Hospital, at Bhopal for his 'vell wishes and true blessings.

New Delhi July 14, 2006

Anil Kumar Tiwari

"

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Abstract

The failure to provide pure water and adequate sanitation services to all people is perhaps the greatest development failure of the 2Oth century. The most egregious consequence of this failure is the high rate of mortality among young children from preventable water-related diseases. According to a new report released by the Paciffic Institute of Oakland, California that over 76 million people will perish fflom water-related disease by 2020 unless urgent action is taken. OEe report ffinds that water-related diseases could claim more lives than the global AIDS pandemic by 2020 unless major changes are made. This problem of non availability of pure water is one of the most serious public health crisis and deserves far more attention and resources than it has received so far.

The causes of the global water crisis are many, but the points to which the attention has to be sought is that the present arrangement to solve this problem has not been found capable enough to ffight this problem because it focuses on large, centralized water puriffication systems and also are highly energy intensive.

The total amount of water available on earth has been estimated at i .4 billion cubic kilometers, enough to cover the planet with a layer of about 3-km deep. About 95% of the earth's water is in the oceans, which is unffit for human consumption and other use because of its high salt content; about 4% is locked in the polar icecaps; and the remaining 1% constitutes all the fresh water in

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drological cycle including ground water reserves. Only 0. 1% is available in as fresh water in rivers, lakes, and streams only suitable for human consumption. OEis highlights the signifficance of the need to ffind out some alternative to get pure water fflom the available brackish water.

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As a solution a lot of attention and money has been diverted on centralized, large-scale water puriffication systems that cannot be built or maintained with local expertise or resources, while traditional and community-scale systems (old concept of solar distillation) have not been given importance to solve the problem. It is time to change direction towards a path that relies on small scale, less energy consuming, decentralized, easy to maintain, and environmental ffliendly solution for obtaining pure water.

The solar still is a best suitable solution of getting pure water from the impure water available. It is one of many processes available for water puriffication, and sunlight is one of the several forms of heat energy that can be used to power that process. Sunlight has the advantage of zero fuel cost.

Solar stills can be used to eLectively remove many impurities ranging fflom salts to microorganisms. Speciffic water quality problems include salinity, iron, manganese, fluorides, heavy metals, bacterial contamination, and pesticide/herbicide residues.

The basic concept of using solar energy to obtain potable water from salty, brackish or contaminated water is really quite simple. Water is left in a closed container under the open sky. It gets evaporated and leaves the water mass.

The function ofa solar still is to capture some how, this evaporated (or distilled) water by condensing it onto a cool surface. Solar energy is used to accelerate the evaporation.

The ultimate aim of most of the research work done in the field of solar distillation is to increase the distillate output from the solar still. This is achieved either by increasing the water temperature or decreasing the condensing cover temperature. Thus any new approach to be employed should attain either one of the

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two objectives effficiently. It can be assumed that higher the solar radiation the higher will be water temperature since they are interrelated. The temperature of water depends on the mass of water in the still, which depends on the depth of water. In addition, the water temperature also depends on the amount of solar radiation received, which depends on the inclination of condensing cover upon which the solar radiation is incident. Consequently, the inclination of the condensing cover and the water depth has been chosen as the main points of interest ofthis research work.

The sun's position changes with change in seasons and as a result, the incident angle of the solar radiation on the cover varies throughout the year.

Therefore an experiment for the whole year has been conducted to study the effect of cover inclination and water depths.

Initially, an indoor experiment for different cover inclinations has been conducted to understand and use the model proposed by Kumar and Tiwari ( 1 996). This numerical model has been chosen for evaluating the different internal heat transfer coeffficients. Cover inclination of 300 was found most suitable inclination for the highest yield and the numerical model has been found capable enough to evaluate the convective and evaporative heat transfer coeffficients accurately that later on used to evaluate theoretical yield. The theoretical and experimental yield has been found agreeing, that proves the suitability of numerical model proposed by Kumar and Tiwari (1 996) for evaluating the internal heat transfer coeffficients.

Outdoor experiments on four single slope passive solar stills were conducted to study the effect ofcover inclination (150, 300 and 450) and water depths (0.02, O.04m, O.08m, O.12m, O.16m and O.18m) on the annual and seasonal performance at the solar energy park of IlT Delhi, India ((latitude 2803 5 ' N, longitude

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77012' E, altitude 216 m from mean sea level). OEe lowest water depth (O.02m) and lowest cover inclination (150) has been found the best suitable for highest annual yield. However the highest cover inclination of 450 has been shown better performance during winter in contrast to i 50 that has shown its superiority on annual as well as in summer season. Higher water depths, in solar still, have shown nocturnal distillation but the same could not contribute much for annual yield.

A thermal model has been developed based on the inner surface cover temperature for predicting the yield as well as various temperatures unlike earlier researchers. This model has been validated successfully for different cover inclinations and water depths for different weather conditions.

Relative dominance of energy fractions of internal heat transfer within the solar still has also been studied for different cover inclinations and water depths for different seasons. The interdependence of all the energy fractions, on water temperature, and their set behavior corresponding to the water temperature, has also been understood that is ffixed, irrespective of the seasons.

On the basis of annual performance shown by different cover inclinations and water depths the size of solar still was optimized to be produced commercially for best performance. The cost per liter and pay back period for this size of solar still has been evaluated by life cycle cost analysis. The lowest cost per liter of Rs 0.3 8 per kg ( 1 kg =1 liter) has been encountered for the lowest system life of 30 years and at lowest rate of interest 4%. If system life increases to 50 years the cost per liter falls down to Rs 0.30 per kg of distilled water at the same interest rate.

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2.3.1 Experimental set-up 2.3.2 Procedure

2 . 3 .3 Instrumentation and observations 2.3.4 Internal estimate of uncertainty

Effect of Inclination of Condensing Cover on Internal Heat and Mass Transfer in Indoor Condition

3. 1 Introduction

3.2 Numerical model for getting "C" and "n"

3.3 Result and Discussion 3.4 Conclusions

Effect oflnclination ofCondensing Cover on Annual Performance

4.1 Introduction

4.2 Goals for studying cover inclinations 4.3 Analysis on observations

4.3. 1 A typical summer observation 4.3.2 A typical winter observation 4.4 Evaluating heat transfer coeffficients 4.5 Annual and seasonal analysis

4.5. 1 Seasonal performance 4.5.2 Annual performance 4.5.3 Analysis ofenergy fraction 4. 5 .4 Validation ofthermal modeling 4.6 Conclusions

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5 Effect of Water Depth on Annual Performance

5.1 Introduction 5.2 Background

5.3 Observational discussions

5.3.1 For typical summer month 5.3.2 For typical winter month

5.4 Evaluating heat transfer coeffficients for different water depths

5.5 Analyzing: annually and seasonally

I 22-155 I 22 i , IL.) 125 125

I-, L)2 I.).) i 37 5.5.1 Analyzing peak months: Summer and winter 138

5.5.2 Performance analysis: Annual 140

5.5.3 Performance analysis: Half yearly i 44 5.5.4 Validation of thermal model: for different water

depths i 45

5.5.5 Studying parametric effect I 50

5.6 Conclusions i 54

Chapter

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6 Techno-Econometric Analysis of Solar Still 6.1 Introduction

6.2 Need oftechno-econometric analysis 6.3 System design and dimensions 6.4 Understanding economics involved

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6.4. 1 .5 Determination of other miscellaneous cost involved, PM1

6.4.2 Maintenance cost for the operation, M%

6.4.3 Salvage value ofa solar still, Ss 6.4.4 Interest rate, i%

6.4.5 Life ofa solar still, n

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6.4.6 Selling price, Si,, 6.4.7 Pay back period, n

6.4.7.1 Ifdistilled water is sold at the price it is produced, CASE -I

6.4.7.2 Ifdistilled water is sold at market price, CASEfr

6. 4.7.3 Ifdistilled water is sold at market price considering interest rate to be zero CASE

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6.5 Result and discussion 6.6 Conclusions

Conclusions and recommendations 174-177

7. 1 Conclusions i 74

7.2 Recommendations I 77

References I 78

Appendix-I I 87

Append

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II I 90

Appendix-Ill i 99

List of publications 202

Reprints/Preprints 203

Brief Bio-Data of author 211