PERFORMANCE STUDY OF VARIOUS DESIGNS OF SOLAR STILL
by
V ija y K u m a r D w iv e d i
Centre for Energy Studies submitted
in fulfillment o f the requirement o f the degree o f Doctor of Philosophy to the
Indian Institute of Technology, Delhi
November 2008
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Certificate
This is to certify that the thesis entitled “Performance Study o f Various Designs of Solar Still” being submitted by Mr. Vijay Kumar Dwivedi to the Indian Institute o f Technology, Delhi, is worthy o f consideration for the award o f the degree o f Doctor of Philosophy and is a record o f bonafide research work carried out by him. He has worked under my guidance and supervision and has fulfilled the requirements, which to my knowledge have reached the requisite standard for the submission o f 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 o f any degree or diploma.
Prof. (DkJIG. N. Tiwari
Professor, Centre for Energy Studies Indian Institute o f Technology, Delhi New D elhi-110016, INDIA
Dated: November i 0 , 2008
Acknowledgements
First o f all, I would like to express my heartiest gratitude and indebtedness to my respected Guide Prof. (Dr.) G. N. Tiwari, who has always shown me the right path, without which, I would not have been able to complete my research work. It was very fortunate that Prof. (Dr.) G. N. Tiwari agreed to become my Supervisor and Philosopher.
I will be grateful to, my respectable Guide through out m y life for his guidance, cooperation and support. I pray for his good health and long life.
I would like to thank Prof. (Dr.) S. C. Kaushik (Head o f Department, Centre for Energy Studies), Prof. (Dr.) A. Chandra and Prof. (Dr.) T. S. Bhatti o f Centre for Energy Studies, for their continuous help and encouragement.
I am very much thankful to, The Management o f Krishna Institute o f Engineering and Technology (K.I.E.T.), Ghaziabad, where I have been working since last eight years.
The K.I.E.T. management has provided financial and moral support, without which it would have been very difficult to complete my Ph.D. work. I will never forget Dr. Ajay Sharma, Director General o f K.I.E.T., who inspired and supported me for Ph.D. work and provided every facility that was required time to time. I am also very thankful to Prof.
(Dr.) P. Chakravorty (Director), Prof. G. S. Sandhu (Ex. - Director), Prof. Gajendra Singh (Additional Director), Prof. (Dr.) K. P. Tyagi (HoD, Mechanical), Mr. Manoj Goel (Chief Administrative Officer), Mr. Manohar Singh, Mr. Manoj Lohumi, Dr. Arvind Tiwari, Mr. Ravi Shankar Prasad, Mr. Vikram Sharma and other colleagues o f K.I.E.T.
I have no words to express my sentiments for my parents who have always loved and encouraged me for higher education. My wife Maithili, sons- Bhavya and Divya,
brother Ajay and Avanindra, brother-in-law Rajesh Mishra, Harish Chand Pandey and Chandramauli Tripathi have always provided moral support and conducive environment throughout my research period. I express high regards to my father-in-law Late Shri T. P.
Tripathi for his blessings and love.
I am also grateful to Mr. Anil Rai, Mr. Swapnil, Mr. Jamil Mr. P. Barnwal and Mr. Lakshmi Chand who helped me in my research work.
I am fortunate to have friends like Mr. Shy am and Mr. Am it, who were always there to support me in moments o f any difficulty.
New Delhi
November 10, 2008
Abstract
The potable water is one o f the basic needs for survival o f human being. All living organisms are predominantly made of water. In fact, water is life. Our drinking water today, far from being pure, contains almost two hundred deadly commercial chemicals and different types o f harmful bacteria and viruses, which make it dangerous for our health. Dufe to fast increase in industrial growth, water pollution is increasing and hence, available water in rivers, lakes and underground water has been polluted. According to a report o f UNICEF more than one billion people live without clean drinking water and more than 2.6 billion people lack adequate sanitation (UNICEF/WHO JMP 2004).
According to WHO 2004 report more than 1.8 million people die every year from diarrhea and 3900 children die every day from water borne diseases.
A lot o f money has been spent in design and development o f centralized large- scale water purification systems that is difficult to maintain with the help o f local expertise and technique. Experiments are being conducted regularly to develop self
sustained system to meet the requirement o f fresh water. Rigorous researches have been carried out by various scientists on design, fabrication and development o f various designs o f solar stills for purification o f saline/brackish/polluted water.
The objective o f most o f the research work carried out in the field o f solar distillation is to increase the distillate yield from the solar still. The distillate yield can be increased either by increasing the water temperature or by decreasing condensing cover temperature. Higher water temperature can be achieved by designing efficient solar distillation systems.
In this research work design, fabrication and performance analysis o f the following solar stills have been discussed.
• Single slope passive solar still,
• Double slope passive solar still, and
• Double slope active solar still under natural circulation mode.
To predict the performance o f single and double slope passive solar still numerous experiments have been conducted at the water depths o f 0.01 m, 0.02 m and 0.03 m in the solar energy park o f Indian Institute o f Technology, Delhi, India (latitude 28°35’ N, longitude 77° 12’ E, altitude 216 m from mean sea level) through out the year starting from October 2005 to September 2006. The single slope solar still was kept facing due south and double slope solar still was placed in east-west direction to receive the maximum possible solar radiation. On the basis o f present studies, it has been found that the double slope passive solar passive still gives higher yield in the summer months (March to June) while single slope passive solar still gives higher yield in the other months. But, the overall annual yield o f single slope passive solar still is higher in comparison to the annual yield o f double slope passive solar still. The annual yield from single slope and double slope passive solar still was observed maximum (499.41 kg) and (464.68 kg) respectively at the water depth o f 0.01 m. The annual yield decreases with increase in water depth for single slope and double slope passive solar still.
Experiments were also conducted on double slope active solar still under natural circulation mode in the campus o f Krishna Institute o f Engineering and Technology, Ghaziabad (U.P), India (28°40’N, 77°25’E, altitude 216 m from mean sea level) starting from January 2008 to June 2008 at the water depth o f 0.03 m and its performance was
compared with double slope passive solar still. The double slope active solar still under natural mode produces almost 1.5 times higher yield than double slope passive solar still.
Analysis o f heat and mass transfer in single and double slope passive solar still have been carried out by different thermal models (Kumar and Tiwari model, Dunkle’s model, Chen model, Adhikari model, Zheng model and Clark’s model) and it was found that Dunkle’s model is most suitable for determination o f internal heat transfer coefficients at the lower water depths (0.01 m to 0.03 m).
Thermal model for double slope passive and active solar still were developed on the basis o f energy balance for different components o f double slope passive and active solar still to evaluate theoretical yield and temperature o f water and condensing covers.
Further, the thermal models for double slope passive and active solar still are validated with experimental results.
Energy and Exergy analysis of single and double slope passive solar still have been carried out on the basis o f annual performance of energy and exergy o f both solar stills. Energy pay back time (EPBT) for single slope and double slope passive solar stills was found 1.91 years and 1.85 years respectively. The thermal efficiency for single and double slope passive solar still was calculated in every month o f a year and it was found that the thermal efficiency o f double slope passive solar still is higher in comparison to the thermal efficiency o f single slope passive solar still.
Based on the monthly data o f yield and embodied energy o f the system, CO2
emission, mitigation and carbon credit earned for different water depth and life o f the system has been evaluated for double slope passive solar still. The carbon credits earned
from double slope passive solar still were found maximum (Rs. 26229.16) at the water depth o f 0.01 m, when the life o f the system was assumed 50 years.
The life cycle cost analysis o f single and double slope passive solar still has also been carried out for composite climate o f New Delhi. The analysis is based on annual performance o f energy and exergy o f both solar stills. It has been observed that water produced by double slope passive solar still is cheaper (Rs. 0.28/kg) than single slope passive solar still (Rs.0.33/kg; Rs. stands for Rupees, an Indian currency). The minimum pay back time o f solar still was found to be 0.61 year, when the distilled water is sold at the market rate (Rs. 10 per kg) considering lifetime o f solar still as 30 years, rate o f interest 4 % and capital cost Rs. 2741.6.
Table of Contents
Page
Certificate i
Acknowledgement ii
Abstract iv
Contents viii
List o f Figures xiii
List o f Tables xvii
Nomenclature xx
CHAPTER-1 GENERAL INTRODUCTION 1-21
1.1 Importance o f Water 2
1.2 Working Principle o f Solar Distillation 6 1.3 Performance Parameters for Solar Distillation 8 1.4 Advantages and Disadvantages o f Solar Still 9
1.4.1 Advantages 9
1.4.2 Disadvantages 9
1.5 Quality o f Water from Solar Still 9
1.6 Application o f Distilled Water 10
1.7 Reasons o f Water Problem 10
1.8 Classification o f Solar Distillation Systems 11
1.9 Literature Review 12
1.10 Objectives o f Research 15
1.11 Thesis Organization 18
CHAPTER-2 DESIGN, FABRICATION, INSTRUMENTATION AND OBSERVATIONS OF SINGLE AND DOUBLE SLOPE
SOLAR STILL 22-47
2.1 Introduction 23
2.2 Design and Fabrication o f Solar Stills 23 2.2.1 Single slope passive solar still 23 2.2.2 Double slope passive solar still 26 2.2.3 Double slope active solar still under natural
circulation mode 28
2.3 Instrumentation 31
2.3.1 Measurement o f temperature 31
2.3.2 Measurement o f distillate yield 32
2.3.3 Measurement o f solar radiation 32
2.3.4 Calibration o f thermocouples 32
2.4 Experimental Procedure 35
2.5 Experimental Observations 35
2.6 Experimental Uncertainty 42
CHAPTER 3 ANALYSIS OF HEAT AND MASS TRANSFER IN SINGLE AND DOUBLE SLOPE PASSIVE SOLAR STILLS 48-65
3.1 Introduction 49
3.2 Thermal Models 51
3.2.1 Dunkle’s model 52
3.2.2 Kumar and Tiwari model 52
3.2.3 Chen et al. Model 54
3.2.5 Zheng et al. model 55
3.2.6 Clark’s model 55
3.3 Results and Discussion 55
3.4 Conclusions 64
CHAPTER 4 THERMAL MODELING OF DOUBLE SLOPE PASSIVE
SOLAR STILL 66-78
4.1 Introduction 67
4.2 Energy Balance Equations for Modeling Double Slope
Passive Solar Still 68
4.2.1 Energy balances on east facing condensing cover 68 4.2.2 Energy balances on west facing condensing cover 69
4.2.3 Energy balances for water mass 69
4.2.4 Energy balances for basin liner 70
4.3 Results and Discussion 72
4.4 Conclusions 77
CHAPTER 5 THERMAL MODELING OF A DOUBLE SLOPE ACTIVE SOLAR STILL UNDER NATURAL
CIRCULATION MODE 79-92
5.1 Introduction 81
5.2 Energy Balance Equations for Modeling Double Slope Active Solar Still Under Natural Circulation Mode 82 5.2.1 Energy balances on east facing condensing cover 83 5.2.2 Energy balances on west facing condensing cover 83
5.2.3 Energy balances for basin liner 84
5.2.4 Energy balances for water mass 84
5.3 Results and Discussion 85
5.4. Conclusions 91
CHAPTER 6 ENERGY AND EXERGY ANALYSIS OF SINGLE AND DOUBLE SLOPE PASSIVE SOLAR STILLS 92-110
6.1 Introduction 93
6.2 Energy Analysis 95
6.2.1 Daily yield o f single and double slope passive solar
Still 95
6.2.2 Monthly and annual yield o f single and double
slope passive solar still 95
6.2.3 Instantaneous thermal efficiency o f a passive solar
still 96
6.2.4 Daily thermal efficiency o f a passive solar still 96
6.3 Exergy Analysis o f Solar Still 96
6.3.1 Instantaneous exergy efficiency o f a passive
solar still 97
6.3.2 Daily exergy efficiency o f a passive solar still 97
6.4 Energy Pay Back Time (EPBT) 98
6.5 CO2 Emission, CO2 Mitigation and Carbon Credit Earned 99
6.5.1 CO2 emission 99
6.5.2 CO2 mitigation 99
6.5.2 C 0 2 mitigation 99
6.5.3 Carbon credit earned 100
6.6 Results and Discussion 100
6.7 Conclusions 108
CHAPTER 7 LIFE CYCLE COST ANALYSIS OF SINGLE AND DOUBLE SLOPE PASSIVE SOLAR STILLS 110-129
7.1 Introduction 111
7.2 Economic Analysis 113
7.2.1 Annual cost o f the passive solar distillation system 113
7.2.2 Pay back time 114
7.3 Capital Cost 115
7.3.1 Cost o f GRP body 116
7.3.2 Cost o f condensing cover 116
7.3.3 Cost o f rubber gasket 117
7.3.4 Cost o f iron stand 117
7.4 Results and Discussion 118
7.5 Conclusions 128
CHAPTER 8 CONCLUSIONS & RECOMMENDATIONS 130-133
8.1 Conclusions 131
8.2 Recommendations 133
