ABSTRACT
Agricultural products upon harvesting have high moisture content which makes it unsafe for storage as the moisture in the crops attracts microorganisms which result in deterioration of the products. The major shortcoming of multiple trays drying is uneven drying of the products being dried on different trays.Solar dryers with and without thermal storage materials were developed, simulated and tested under the same meteorological conditions of Zaria and their performance evaluation were carried out. The average drying rates, collector efficiencies, and drying efficiencies of the solar crop dryers with and without thermal storage are 2.82×10−5 kg/s and 2.55×10−5 kg/s, 78.25% and 42.20%, 29.15 % and 25.35% respectively. During the experiment, the drying rates do not vary much with the coordinate positions of the trays. The performances of the solar dryers were simulated under varying meteorological conditions of Zaria. TRANSYS 16.0software was used to simulate the collectors‟ outlet air temperatures with and without thermal storage. Since a drying model is not available in the TRNSYS library, MATLAB code was written to computes the weight loss of the yam slices in the drying chamber. The computedNash-Sutcliffe Coefficient of Efficiency (NSE) values and its correspondingRoot Means Square Errors(RMSE) between the modeled collector air temperature, and the observed collector air temperature, with and without thermal storage confirms that the model formulation using TRANSYS 16 software used here for the performance simulation of the system is valid and realistic owing to the good quality of fit between the experimental and the simulated results. Similarly, the computed NSE values and its corresponding RMSE between the modeled weight loss of yam slices, and the observed weight loss of yam slices, with and without thermal storage follow the same trend
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TABLE OF CONTENTS
COVER PAGE ………………………………………………………. Error! Bookmark not defined.
TITLE PAGE ………………………………………………………… Error! Bookmark not defined.
DECLARATION …………………………………………………………………………………………….. iii
CERTIFICATION …………………………………………………………………………………………… iv
DEDICATION ………………………………………………………………………………………………….v
ACKNOWLEDGEMENT ………………………………………………………………………………… vi
ABSTRACT ………………………………………………………………………………………………….. vii
TABLE OF CONTENTS ………………………………………………………………………………… viii
LIST OF FIGURES …………………………………………………………………………………………. xi
LIST OF TABLES ………………………………………………………………………………………… xiii
LIST OF PLATE …………………………………………………………………………………………….. xv
LIST OF APPENDICES …………………………………………………………………………………..xvi
NOMENCLATURE ……………………………………………………………………………………… xvii
CHAPTER ONE………………………………………………………………………………………………..1
INTRODUCTION ……………………………………………………………………………………………..1
1.1 Background of the Study ………………………………………………………………………………..1
1.2 Problem Statement ………………………………………………………………………………………..3
1.3 Present Research …………………………………………………………………………………………..4
1.4 Aim and Objectives ………………………………………………………………………………………4
1.5 Justification …………………………………………………………………………………………………5
1.6 Scope of the Study ………………………………………………………………………………………..5
CHAPTER TWO ……………………………………………………………………………………………….6
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LITERATURE REVIEW ……………………………………………………………………………………6
2.1 General Introduction on Yam ………………………………………………………………………….6
2.2 Solar Dryers and Drying Principle …………………………………………………………………..6
2.3 Classification of Drying Systems …………………………………………………………………7
2.3.1 Types of Solar Dryer …………………………………………………………………………………..9
2.4 Theoretical Background of Solar Energy ………………………………………………………… 12
2.4.1 Solar constant …………………………………………………………………………………………. 12
2.4.2 Declination …………………………………………………………………………………………….. 12
2.4.3 Incidence angle ……………………………………………………………………………………….. 14
2.4.4 Hour angle(𝝎) ………………………………………………………………………………………… 14
2.4.5 Sunset hour angle (𝝎𝒔) …………………………………………………………………………….. 15
2.4.6 Extraterrestrial solar radiation on a horizontal surface ……………………………………. 15
2.4.7 Solar radiation at the earth surface ……………………………………………………………… 15
2.4.8 Direct solar radiation ………………………………………………………………………………… 16
2.4.9 Diffuse solar radiation ………………………………………………………………………………. 17
2.4.10 Ratio of beam and diffuse radiation on tilted surface to that on the horizontal ….. 17
2.5 Thermal Storage ………………………………………………………………………………………… 18
2.6 Review of Related Past Work ………………………………………………………………………. 20
2.6.1Direct Mode Solar Dryers ………………………………………………………………………….. 20
2.6.2Indirect Mode Solar Dryers ………………………………………………………………………… 21
2.6.3Summary of the Solar Dryer Review ……………………………………………………………. 24
CHAPTER THREE …………………………………………………………………………………………. 25
MATERIALS AND METHOD …………………………………………………………………………. 25
3.1 Description of the Two Solar Crop Dryers …………………………………………………….. 25
3.2 Working Principle ……………………………………………………………………………………… 27
3.3 Materials …………………………………………………………………………………………………… 28
3.3.1 Material Selection ……………………………………………………………………………………. 28
3.4 Design Considerations ………………………………………………………………………………… 30
3.5 Design Theory …………………………………………………………………………………………… 32
3.5.1 Solar Radiation ……………………………………………………………………………………….. 32
3.6 Design Procedure for the Solar Dryers …………………………………………………………… 33
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3.6.1 Solar Collector Design ……………………………………………………………………………… 33
3.6.2 Drying Chamber Design …………………………………………………………………………… 36
3.6.3 Performance Evaluation of the Crop Dryers …………………………………………………. 41
3.7 Heat Loss from the Collector ……………………………………………………………………….. 43
3.8 Design Calculations ……………………………………………………………………………………. 44
3.9TRANSYS Simulation of Solar Collectors ………………………………………………………. 49
3.10 Drying Modelling …………………………………………………………………………………….. 53
3.11 Error Analysis and Validation of Simulation Model in Comparison with the Experimental Results …………………………………………………………………………………….. 54
3.12 Solar Crop Dryer Construction ……………………………………………………………………. 56
3.13 Cost Analysis …………………………………………………………………………………………… 59
3.14 Yam Tuber Sample Preparation ………………………………………………………………….. 60
3.15 Instrumentation of the Solar Dryers……………………………………………………………… 60
3.16 Testing and Performance Evaluation ……………………………………………………………. 61
CHAPTER FOUR …………………………………………………………………………………………… 64
RESULTS AND DISCUSSION ………………………………………………………………………… 64
4.1 Results ……………………………………………………………………………………………………… 64
4.1.1 Simulated and Experimental Results for the Solar Dryers ……………………………….. 64
4.1.2 Error Analysis of the Comparison between Experimental and Simulated Results .. 76
CHAPTER FIVE …………………………………………………………………………………………….. 83
SUMMARY, CONCLUSION AND RECOMMENDATIONS ……………………………….. 83
5.1 Summary ………………………………………………………………………………………………….. 83
5.2 Conclusion ………………………………………………………………………………………………… 84
5.3 Recommendations………………………………………………………………………………………. 85
REFERENCES ……………………………………………………………………………………………….. 86
APPENDICES ………………………………………………………………………………………………… 91
CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Solar thermal technology is rapidly gaining acceptance as an energy saving measure in agricultural application. It is preferred to other alternative sources of energy because it is abundant, inexhaustible and non-polluting (Bukola and Ayoola, 2008). In Nigeria, just like several other developing nations, agriculture is considered a factor for growth and development. The country is blessed with a landmass of 98.3 million hectares of which 72% is considered suitable for agricultural production(Aasa et al., 2012). However, the rate of growth has been attributed to the level of agricultural preservation in the country. Her poor record of food preservation has led to improper management of agricultural produce and this impinged on the growth of food production (Aasaet al., 2012). After agricultural products are harvested, there is the need for proper storage for future use. The products upon harvesting have high moisture content which makes it unsafe for storage as the moisture in the crops attracts microorganisms which result in deterioration of the products. Among other reasons, crops are dried to improve shelf life, retain original flavor and reduce weight for easy transport and trade. Drying ensures water evaporation from agricultural products to the drying medium- usually hot air. Drying plays a vital role in the preservation of agricultural products (Amma, 2014).
Conservatively, many cereal crops, vegetables and fruits are dried by thinly spreading them on a prepared ground, mats, and paved ground in open sunlight. Large losses are generally incurred as a result of using this method. The losses are attributed to birds,
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rodents, domestic animals and the wind blowing the product beyond recovery (Bolaji, 2005). High humidity levels associated with tropical environments has been contributing immensely to crop lost to fungal and microbial degradation (Drew, 2011). The further disadvantage of this open air sun drying technique is lack of control over the drying rate which results in under drying or over drying (Bolaji, 2005). Controlled Solar drying gives quality end product, rapid drying and more hygienic product. Many dryer types have been in used in both domestic and industry sectors. The simplicity of design and economic consideration make cabinet dryer most extensively used. A cabinet dryer consists of several stacks of trays placed in an insulated chamber in which hot air is distributed by a fan or natural flow (Mishaet al., 2013). The major shortcoming of the cabinet dryer is uneven drying because of poor air flow distribution in the drying chamber. Good air flow distribution in the drying chamber will help in attaining uniform moisture contents of the products being dried on different a tray. Solar energy application requires efficient thermal energy storage so that the excess heat collected during high insolation may be stored for later use during low insolation, cloud cover, rains and even in the night. Due to the intermittent nature of solar energy, an integration of energy storage material with the solar collectors is necessary in order to make the solar energy source more consistent (Kambleet al., 2013).
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1.2 Problem Statement
The inadequate method of preserving agricultural produce which is usually produced in larger quantities during harvest has remained one of the main problems facing Nigerian farmers. High crop losses due to inadequate drying, fungi attacks, insects, birds, rodent encroachment and unpredictable weather effects such as dust, rain, and the wind have remained some of the inherent limitations of the traditional open sun drying method widely being practiced by rural farmers (Eze and Agbo, 2011). The open sun drying also results in physical and structural changes in the agricultural produce such as unnecessary shrinkage, case hardening and loss of volatiles and nutrient components. (Rajkumar, 2007).Therefore, a control mode of drying which preserves the color, nutrient components and unnecessary shrinkage of the agro-produce is necessary. One of these control modes involves constructing a solar crop dryer. Different types of dryers were developed at different times and places in the world. The problem of most of these dryers is the variation of the final moisture content of the dried product at different trays position due to the poor airflow distribution, especially in a typical cabinet dryer. As the drying air goes up from the bottom tray to the upward tray, the drying rate decreases. This is because the drying air temperature into the upper tray is lower than that of the bottom tray, and also the drying air is relatively wet. Therefore, there is need to improve on the existing ones that can solve or mitigate this problem of non-uniform drying.
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1.3 Present Research
The present work is concerned with the design, simulation, construction, and performance comparison of mixed-mode solar crop dryers with and without thermal storage. Two separate dryers were built; one with plane conventional flat plate absorber and the other with flat plate absorber integrated with thermal storage material. An experimental test of the dryers was done to validate the simulated results using TRANSYS 16.0 and MATLAB R2013a Softwares.
1.4 Aim and Objectives
The aim of the work is todesign, simulate,construct and carry out the performance comparison of mixed-mode solar crop dryers with and without thermal storage material integrated with the absorber for yam drying under the meteorological conditions of Zaria. The specific objectives are to:
i. Carry outdesign analysis to determine the dimensions of the solar crop drying systems;
ii. Simulate the performance of the drying systems with and without thermal storage material under varying meteorological conditions of Zaria;
iii. Construct solar crop dryers with and without thermal storage materials; and
iv. Evaluate experimentally the performance of the solar dryers.
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1.5 Justification
The escalation of fuel cost, fossil fuel depletion and high pollution potential of conventional fuels to the environment has resulted in a search for a safe alternative fuel for dryers. Solar energy is one of the most promising renewable energy sources in the world because of its abundance, inexhaustible and non-pollutant in nature compared with higher prices and shortages of fossil fuels (Rajkumar, 2007). The present study will address the problem of nonuniform drying in different trays coordinate position in solar cabinet dryer. The drying efficiency and uniformity in drying of the dried product depend on airflow distribution into the drying chamber. Proper airflow distribution will help in attaining uniform drying rate of the product being dried in the solar crop dryer and hence solve the problem of variation of moisture content of the product in the different trays coordinate position.
1.6 Scope of the Study
The scope of this research work is limited to design, simulation, construction and performance comparison of mixed-mode solar crop dryers with and without thermal storage. Using typical meteorological year (TMY) data of Zaria, TRANSYS 16.0 and MATLAB R2013a Softwares were used to predict the performance of the dryers. Performance evaluation covered determination of the amount of moisture loss, drying rate, collector efficiency and drying efficiency.
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