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APPLICATION OF GREENHOUSE

FOR

CROP PRODUCTION AND DRYING

by

DILIP JAIN

Centre for Energy Studies

Submitted

in fulfillment of the requirements of the degree of

Doctor of Philosophy

to the

Indian Institute of Technology Delhi

July 2002

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© Indian Institute of Technology, New Delhi, 2002

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A'Y FP CCESSED

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Certificate

This is certified that the thesis entitled "Application of Greenhouse for Crop Production and Drying" being submitted by Dilip Jain 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 the original bonafide research work carried out by him under my guidance and supervision.

The results contained in the thesis have not been submitted in part or full, to any other University or Institute for the award of any degree or diploma.

Cc:101 D .N. Tiwari Professor

Center for Energy Studies Indian Institute of Technology Hauz Khas, New Delhi 110 016 Date: 1 July 2002

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Acknowledgements

I acknowledge the path and the energy that one gets through the grace of God for fulfilling research work. I acknowledge His love, He showers on all and lead me to work through out this period.

I express my deep sense of gratitude to Professor G.N. Tiwari for his constant inspiring guidance and utmost cooperation at every stage in successful completion of this research work.

I express my sincere gratitude to Dr. S.M. Ilyas Director and Dr. B.S. Bisht Ex-Director, Central Institute of Post Harvest Engineering and Technology, Ludhiana (ICAR) for deputing me to pursue the Ph.D. degree and for their keen interest and help rendered during the research work.

I am very much thankful to Prof, S.C. Mullick, Head, Prof D.P. Kothari, Prof.

S.C. Kausik, Prof A. Chandra and Prof. J.C. Joshi of CES for their kind advice and timely help. My sincere thanks to Prof. V.K. Srivastava and Prof A. K. Gupta, Department of Chemical Engineering and Prof. G. Deshmukh, Department of Mechanical Engineering for their academic discussion and encouragement.

My special thanks are due to my colleagues at CIPHET, Ludhiana and my 'friends Mr. Manu Sharma, Mr. Nirupam Rohatgi, Mr. M.K. Goshal and many others for their valuable assistance and fruitful discussion throughout the course of study.

I have no befitting words to express my deep sentiments towards my mother, wife Rekha, sons Sidhant and Vedant for their wholehearted support and patience during the period of study.

My wife joins me to extend our deep sense of obligation and regards to Mrs.

Tiwari and family members for their high order of hospitality and encouragement throughout our stay in Delhi.

Last but not least, I convey my sincere thanks to Mr. Dhaney Singh, Mr.

Lakhmi Chand, Mr. Shankar Lai and staff member of IIT, Delhi for their kind support and help in completing this work.

Date: 1 July 2002 (Dilip Jain)

ii

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Abstract

In tropical countries like India the application of greenhouses is limited because of prevailing extreme weather conditions in summer and winter. Heating and cooling of greenhouses are therefore important aspects for their efficient use and wide applicability. Crop drying is another important process, where the applicability of greenhouses can be extended, since the greenhouses are the effective solar energy collector. Very limited work on crop drying in greenhouses has so far been attempted in India.

The experimental studies have been conducted to optimize the parameters of one of the heating and cooling systems in a greenhouse, and also to evaluate the convective mass transfer coefficient for drying of cabbage and peas in the greenhouse.

Appropriate mathematical models have been developed to study the thermal behavior of the greenhouse during these processes. An even-span greenhouse has been considered for experimental purposes and thermal modeling. A ground air collector was used 'for heating of greenhouse in winter. A fan and pad type evaporative cooling system was provided for cooling the greenhouse in summer. A simulated study of crop drying has been attempted with the smaller size of even-span greenhouse.

For heating of the greenhouse, parameters such as area of ground air collector;

mass flow rate and heat capacity have been optimized against behavior of the plant and room air temperature and thermal load leveling. The stored thermal energy of ground collector proved useful in increasing the temperature by 7 from the ambient temperature during night. The optimum area of ground air collector, mass flow rate and heat capacity were obtained as 17.55 m2, 200 kg/hr and 20950 UT, respectively for the even-span greenhouse (ridge height 3m and walls height 2m with floor area 6x4 m2).

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Abstract

The cooling system (fan and pad) parameters like length of greenhouse (for effect of cooling length), height of cooling pad and mass flow rate have been optimized against the maximum temperature and thermal load leveling by dividing the greenhouse into two zones- zone-I and zone-IL The average temperature drop in greenhouse was 5 °C from the ambient temperature during daytime in summer. The temperature was lowest near the cooling pad and increased while going away from the cooling pad (along the length of greenhouse) as expected. The optimum parameters of cooling system were found to be (i) 6 m length of the greenhouse, (ii) mass flow rate as 0.6 kg/s, and (iii) 1.5 m height of cooling pad (width 3 m) o the given greenhouse.

For cabbage and peas, the convective mass transfer coefficient in greenhouse drying under forced mode doubled over the natural convection in the initial stage of drying. Its value ranged from 38 W/m2 °C to 1 W/m2 °C from the beginning towards the end of the drying period. The behavior of convective mass transfer coefficient in the beginning of drying was like that of a wetted surface and at the end of the drying like of dry surface. The convective mass transfer coefficient as a function of drying time has been established with the help of a two-term exponential curve model. For drying of crop produce, three simple mathematical models were developed to predict the crop temperature, greenhouse room air temperature and moisture evaporation for open sun drying (natural convection), greenhouse drying under natural and forced convection. These models were validated with experimental observations for drying of cabbage and peas with each mode of drying. The predicted values showed good agreement with experimental observations with positive coefficient of correlation for crop temperature (r =0.96), greenhouse air temperature (r =0 .97) , and rate of moisture evaporation (r =0.99) for all the three drying methods.

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Abstract

The present studies amply indicated that greenhouse can be efficiently used for crop production providing moderate heating (ground air collector) and cooling (fan and pad evaporative cooling) systems. Such greenhouses can also be used for effective crop drying under forced convection to enhance the drying.

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Contents

Table of Contents

Certificate

Acknowledgements Abstract

Nomenclature

Chapter I 1

General Introduction

1.1 Importance of greenhouse 1

1.2 Definition of greenhouse 3

1.3 Application of principle of greenhouse 4

1.3.1 Solar crop cultivation 4

1.3.2 Solar crop drying 6

1.4 Classification of greenhouse systems 7

1.5 Basic heat and mass transfer 9

1.5.1 Radiative heat transfer coefficient 9 1.5.2 Convective heat transfer coefficient 10 1.5.3 Conductive heat transfer coefficient 12 1.5.4 Evaporative heat transfer coefficient 12

1.6 Basic energy balance equations 13

1.6.1 For crop production in greenhouse under steady-state 13 condition

1.6.2 For open sun drying 14

1.6.3 For crop drying in greenhouse 14

1.7 Statistical tools 14

1.7.1 Experimental uncertainty 14

1.7.2 Mean square deviation as z-square 16 1.7.3 Root mean square of percent deviation 16

1.7.4 Coefficient of correlation 16

1.8 Scope of the present studies 17

vii

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Contents

Chapter II 19

Thermal modeling and optimization of greenhouse parameter integrated with ground air collector

2.1 Introduction 19

2.2 Review of literature 20

2.3 Identification of problem 23

2.4 Working principle of ground air collector 24

2.5 Design of experimental greenhouse 25

2.5.1 Greenhouse 25

2.5.2 Ground air collector 27

2.6 Parameters and their measurements 27

2.6.1 Solar radiation 27

2.6.2 Temperature 28

2.7 Experimental observation 30

2.8 Thermal analysis 30

2.8.1 Energy balance equations 30

2.8.2 Useful energy gain 32

2.8.3 Thermal load leveling 34

2.9 Computational procedure and input parameters 34 2.9.1 Evaluation of solar radiation on different walls and 38

roofs

2.9.2 Determination of solar fraction (Fn) 39 2.9.3 Example of evaluation of heat removal factor 39 2.9.4 Determination of experimental error 41

2.10 Results and discussion 43

2.10.1 Hourly variation of plant and room temperature 43 2.10.2 Optimization of ground air collector parameters 47 2.10.3 Evaluation of threshold solar intensity 52 2.10.4 Effect of ground air collector on room temperature 54

2.11 Conclusions 55

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Contents

Chapter III 57

Modeling and optimal design of evaporative cooling system in greenhouse

3.1 Introduction 57

3.2 Review of literature 58

3.3 Identification of problem 61

3.4 Working principle of fan-pad evaporative cooling system 62 3.4.1 Fan and pad evaporative cooling systems 63

3.5 Design of experimental greenhouse 64

3.5.1 Greenhouse 64

3.5.2 Fan and pad cooling system 64

3.6 Parameters and their measurements 66

3.6.1 Solar radiation 66

3.6.2 Temperature 66

3.7 Experimental observation 66

3.8 Thermal analysis 67

3.8.1 Energy balance equations 67

3.8.2 Thermal load leveling 71

3.9 Computational procedure and input parameters 71 3.9.1 Evaluation of solar radiation on different walls and 74

roofs

3.92 Determination of experimental error 74

3.10 Results and discussion 75

3.10.1 Variation of room temperature after evaporative 75 cooling

3.10.2 Optimization of evaporative cooling parameters 80

3.11 Conclusions 87

ix

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Contents

Chapter IV 89

Evaluation of convective mass transfer coefficient for cabbage and peas drying: Natural and forced mode

4.1 Introduction 89

4.2 Review of literature 91

4.3 Identification of problem 93

4.4 Design of experimental greenhouse 94

4.5 Parameters and their measurements 97

4.5.1 Solar radiation 97

4.5.2 Temperature 97

4.5.3 Humidity/Relative humidity 97

4.5.4 Weight 99

4.5.5 Air velocity 99

4.6 Theory 99

4.6.1 Determination of convective mass transfer coefficient 99

4.6.2 Exponential curve fitting 102

4.7 Experimentation 103

4.7.1 Sample preparation 103

4.7.2 Experimental observation 103

4.8 Computation technique 107

4.8.1 Determination of experimental error 108

4.9 Results and discussion 110

4.9.1 Heat transfer in greenhouse drying 110 4.9.2 Convective mass transfer coefficient under natural 114

convection

4.9.3 Convective mass transfer coefficient under forced 119 convection

4.9.4 Exponential curve fitting 122

4.10 Conclusions 122

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Contents

Chapter V 123

Thermal behavior of crop drying under open sun and inside the greenhouse

5.1 Introduction 123

5.2 Review of literature 124

5.3 Identification of problem 127

5.4 Working principle of solar crop drying 128

5.5 Thermal modeling 130

5.5.1 Thermal modeling of open sun drying 130 5.5.2 Thermal modeling of greenhouse drying under natural 132

mode

5.5.3 Expression of coefficient of diffusion 133 5.5.4 Thermal modeling of greenhouse drying under forced 134

mode

5.6 Input values and computational procedure 135 5.7 Determination of coefficient of diffusion under natural mode 140

5.8 Results and discussion 141

5.8.1 Open sun drying 141

5.8.2 Greenhouse drying under natural convection 143 5.8.3 Greenhouse drying under forced convection 144

5.9 Conclusions 146

Chapter VI 147

Conclusions and Recommendations

6.1 Conclusions 147

6.2 Limitations 149

6.3 Recommendations 149

References 151

Appendices 165

Reprints / preprints 175

Brief bio-data of the author 181

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