DESIGN, CONSTRUCTION, SIMULATION AND PERFORMANCE EVALUATION OF A SOLAR BOX COOKER

ABSTRACT

A solar box cooker is a device that converts solar energy into useful heat in a confined space. The solar cooking system which captures and utilizes the abundant solar energy was designed, simulated, constructed and tested. Plane reflectors were used to concentrate solar radiations continuously on the collector which result to heat gain. It is usually difficult to manually track the movement of the sun and the use of a tracking device may be very expensive. Hence, plane reflectors were used.

At the initial stage, the typical metrological year (TMY) solar data of Zaria obtained was processed to obtain the monthly average daily solar resources of Zaria using the solar radiation and weather data processor TYPE 109 component of TRNSYS 16 software. The month with the least average daily solar radiation was considered as the design month and the result shows that the month of August has the least solar radiation and therefore, considered as the design month. Secondly, the solar cooker was constructed at Ahmadu Bello University, Zaria Mechanical Engineering Workshop using various tools for cutting and machining.

Thirdly, the solar cooker was tested at Mechanical Engineering Department of ABU between 28th and 31st of October, 2016. During the course of the testing, it was observed that in general the performance of the cooker was so encouraging because it cooked rice within an hour. The maximum stagnation temperature and that of absorber plate temperature were found to be 141oC and 143oC respectively.

The cooker was simulated using TRNSYS and EES software. The simulated results were compared with the experimental results to determine the level of agreement between the two using Root Mean Square Error (RMSE) and Nash Sutcliffe Efficiency (NSE) statistical tool.

The RMSE results are 4.8203oC and 2.604oC. While the NSE results are 0.9867 and 0.996. These results show that the experimental values and the simulated values are in good fit.The regression line for the experiment and simulation were obtained and were used to compute the cooking power of the cooker. At 50oC, the experimental and simulated cooking powers are 52.8W and 54.8W respectively.

For the average solar radiation incident on surfaces at different time intervals for the 4 conservative days, the regression line showing line of best fit for the co-efficient of determination (r2) was found to be 91.87%. And also, for the variation of simulated and experimental collector efficiency, the co-efficient of determination (r2) for both the simulated and experimental results were found to be 98.8 and 94.1% respectively. And the percentage of energy increment due to third reflector was found to be 84.5%.

CHAPTER ONE

INTRODUCTION

1.1 Background to the Study

Energy is a thermodynamic quantity which is described as the capacity of a physical system to do work. Energy is vital for our relations with the environment, and thus the research to resolve problems related to energy is quite significant since life is directly affected by energy and its consumption. Fossil fuel based energy resources still predominate with the highest share in global energy consumption (Chinnumol and Victor, 2015). An enormous amount of energy is thus expended regularly on cooking. In almost all the rural homes and many urban homes in Nigeria, the traditional and most popular source of energy for cooking is firewood (Kulla, 2011). The projected wood consumption in Nigeria for the year 2000 was 23.6 million tonnes of oil equivalent (Ekechukwu and Abdussalam, 2001).

Desert encroachment and global warming are few among many resultant effects. Most urban dwellers also use kerosene and other petroleum bye products for cooking amidst its attendant environmental hazards. Fossil fuels are not environmentally friendly owing to emissions arising from bye products of combustion which constitute health hazards (Basil, 2013). The energy required for cooking is supplied by non-commercial fuels like firewood, agricultural waste, cow dung and kerosene (Erdem and Pinar, 2013).

Nigeria is blessed with a significant level of solar insolation. The country receives about 5.08 x 10¹² KWh of energy per day from the sun (Aremu and Akinoso, 2013). The technology of solar cooking involves the conversion of solar energy to heat energy. The heat is then directed to cooking pot for food preparation. Solar cooking systems could be box type, concentrating type or a hybrid of the two. Box-type solar cooker makes use of both diffuse and direct radiation while the concentrating type depends on its ability to make use of direct radiation only (Aremu and Akinoso, 2013).

Solar energy is one of the main alternative renewable sources of energy crucial to our search for domestic fuel replacements. This is because; it is the source of almost all renewable and non-renewable sources of energy. Also, it is the cleanest, free from environmental hazards and it is readily available and inexhaustible (Bello et al., 2010).

Solar energy presents an alternative energy source for cooking, which is simple, safe and convenient without consuming fuels and polluting the environment. It is appropriate for Hundreds of millions of people around the world with scarce fuel and financial resource to pay for cooking fuel (Chinnumol and Victor, 2015). Solar cookers can also be used for boiling of drinking water, providing access to safe drinking water to millions of people thus preventing water-borne illnesses (Chinnumol and Victor, 2015).

Solar cookers are heat exchangers designed to use solar energy in cooking process (Haftom et al., 2014). In supplying the needed energy, solar cookers can fully or partially replace the use of firewood for cooking in many developing countries (Haftom et al., 2014).Cooking is the art, technology and craft of preparing food for consumption with the use of heat. Cooking techniques and ingredients vary widely across the world, from grilling food over an open fire to using electric stoves, to baking in various types of ovens, reflecting unique environmental, economic and cultural traditions and trends (SC, 2016).

Solar cooking is the simplest, safest, most convenient way to cook food without consuming fuel or heating up kitchen. Many people choose to solar cook for these reasons. But for hundreds of millions of people around the world who cook over fires fuelled by wood or dungs, and who walk miles to collect fire wood or spend much of their meagre income on fuel, solar cooking is more than a choice-It is a blessing (SC, 2016).

1.2 Problem Statement

Cooking using firewood has led to wood shortages (Aremu and Akinoso, 2013).In meeting the essential and basic need of human being, wood and fossil fuel as sources of energy for cooking food have played tremendous and invaluable roles. However, the direct combustion of wood and fossil fuel as the major sources of cooking has immensely contributed to global warming and acid rains (Sobamowa et al., 2012). Aside from these adverse effects of global warming, the inhalation of these gases irritates the lungs and the eyes and can cause diseases such as pneumonia (Sobamowa et al., 2012).

Electric cookers are also source of heat energy. But unfortunately the high cost of electric energy generation and distribution added to erratic power supply, which constitute obvious drawbacks. Nigeria as well as other countries in the tropics is readily blessed with abundant supply of solar energy which can conveniently be harnessed to fill this gap (Basil, 2013). About two billion people are daily dependent on firewood as a source of their domestic and heating energy. They live in the tropics which are the most favourable area for harnessing solar energy (Ohajianyaet al., 2014). Therefore, there is need for developing solar stoves to harness the available solar energy. However, some solar cookers use only one reflector which results to low solar radiation. Therefore, the radiation can be improved by increasing the number of reflectors which result to high absorber plate temperature into the cooking chamber.

1.3 Present work

The present work is to design, simulate, construct and evaluate the performance of a box solar cooker using three reflectors. The Box solar cooker was built using three reflectors and plane mirrors were used to serve as booster of solar radiations to the cooking chamber. Ply wood was used to build the inner and outer casing and good insulating material (fibre glass) was inserted in between the casing to minimize heat loss. Double transparent glass (window frame) on top of the cooker was served as top cover that let in sunlight. However, absorber plate was attached to the inner box casing and served as the cooking chamber were the cooking chamber was coated with matte black colour for better heat absorption. A mathematical model using TRNSYS simulation based programme and Engineering Equation Solver (EES) was used to simulate the components of the cooker to compare with constructed components.

1.4 Aim and objectives

The aim of the project is to design, simulate, fabricate and carry out the performance evaluation of box solar cooker using three plane reflectors to achieve cooking under Zaria metrological condition.

Specific objectives are to:

1. Carry out design analysis to determine the dimensions of solar cooking system.
2. Simulate the design and evaluate performance of the collector under Zaria metrological condition.
3. Construct and carry out performance evaluation of the solar cooker.

1.5 Justifications

No petroleum, diesel or any artificial form of fuel required to use in solar cooker. But rather, it uses sunlight which is in abundant. Many profit organisations are promoting their use worldwide in order to help reduce fuel cost and to avoid air pollution. The use solar cooker in homes dramatically lead to decrease in illegal electrical connections and consequent fire outbreak. Solar cooking systems can operate for many years without requiring any serious maintenance. So therefore, very little service or maintenance is required for the life of the system. Solar cooker produces no waste products such as carbon dioxide or other chemical pollutants, so has minimal negative impact to the environment. Use of solar energy slows down:

1. Deforestation: clearing earth‟s forest on a massive scale often resulting in damage in the quality of the land.
2. Desertification: process by which fertile land becomes desert, typically as a result of drought, deforestation and in appropriate agriculture.

The use of solar energy helps in reducing electricity consumption. The saved energy could be used for other activities (Mohammed, 2015).

1.6 The Scope of the Study

The work done covers the following areas:

1. Design and selection of materials at a specified dimension.
2. Simulation of the solar cooker.
3. Performance evaluation of the cooker.