“Experiment Analysis of Box Type Solar Cooker with and without Thermal Energy Storage Medium”

Abstract

Energy plays a vital role for cooking purpose. This study is focused on the performance analysis of box type solar cooker at the climate conditions of Gwalior. Thermal energy storage materials provide better temperature and reducing cooking time as compared to without TES. In this thesis, two different types of TES material are used i.e. water and sand and the performance of solar cooker with TES and without TES are compared, the maxi mum temperature is attained by the solar cooker without TES was found 90.6oC when solar radiation was 1075 w/m2 while using sand and water as TES the maximum temperature was found 81.3°C and 69.4oC respectively when solar radiation was found very low 496 w/m2 and 365 w/m2 .It seems that where radiation is low and off-sunshine, TES material is used for attaining maximum temperature. The sand gains the temperature faster than the water but it needs to be moisture free. The advantage of using water is that even though there occurs a sudden fall in solar radiation, the water temperature remains the same for a long duration, which is not possible in case of cooker without thermal energy storage.

Introduction

I. INTRODUCTION

Cooking is a heat treatment process of raw food, and depending on the temperature requirement, method of heating, and duration, cooking may be categorized as baking, roasting, boiling, blanching, etc. Besides, household cooking, it is performed in an institutional and community kitchen. This has given an opportunity for solar cooking to prove environmentally and economically beneficial. Various studies have shown that solar cooking and heating contributes to carbon mitigation [1,2]. Solar cooking is a part of India's energy expansion program in the energy security area. Energy consumption for cooking accounts for 36% of the total energy demand in India. The use of solar energy will reduce the burden on LPG and fossil fuel consumed. The main obstacle in the acceptance of solar energy is a convenience issue and high initial cost of solar cookers. The development in concentrated solar technology could overcome the limitations of the conventional box cooker [3]. Concentrated solar power has offered many benefits in large-sized kitchens where people take their meals. Steam at high temperature and pressure produced using the solar concentrators transferred to the kitchen for food cooking. Concentrated solar energy has proven the best clean and economical energy source for cooking; its use can be expanded to post-harvesting agricultural produce such as turmeric cooking/blanching [4].

II. RESEARCH GAPS IN SOLAR COOKERS WITH THERMAL ENERGY STORAGE

1. There have been limited research studies on solar cookers with TES systems using heat transfer oils. Heat transfer oils are particularly favorable since temperatures above the boiling point of water (100oC) can be achieved which are suitable for frying and baking. Besides this, storage tanks using oil are simplified since they do not have to be pressurized as with the case of water which is cheaper and readily available [5].
2.  The use of locally available TES materials in a particular region or country for enhancing the performance of solar cookers is rather limited [6].
3.  Packed bed storage systems using oil heat transfer fluids for domestic cooking applications have been rarely reported in recent literature. The packed bed storage configuration has better heat transfer characteristics than other types of configurations such as the shell and tube especially when latent heat thermal energy storage systems are considered [7].
4.  Storage type of cooking vessels has been rarely reported. These vessels can store  heat during periods of high solar radiation, and use it during non-sunshine periods.
5. Hybrid solar cooking and TES storage systems using another energy source have been rarely reported. These systems are more practical especially when there are extended periods of low solar radiations. The alternative energy source can be used for cooking [8].
6.  TES applications of metallic phase change materials (PCMs) for higher volumetric storage densities and higher thermal conductivities that have appeared in recent literature are rather limited [10].

The box type solar cooker of dimensions 600mm × 600mm × 200mm facing south is used as shown in the Figure 3.1. The box is fitted with a 2cm thermocol sheet and a 2cm thermocol sheet. The absorber tray is made aluminum sheet of 0.5mm thickness, which is a black powder coated. Similarly, cooking utensils are made of black powder coated stainless steel. It consists of one reflector mirror and two transparent glasses. The experiment is performed in the summer at the terrace of Madhav Institute of Technology & Science, Gwalior. The setup is shown in Figure 1.

Cooking capacity is about 1 kg at a time or 3-4 kg per day depending on the intensity of the radiation. The absorption tray material should have high absorption and low ventilation, to help block radiation inside the solar cell [10]. The dark cover of the absorber plate and the cooking vessel enhances absorption of the solar radiation by a type of solar cooker. The solar cooker cover is made using double-glazed glass, with long beams, and is exposed to high energy, short rays of the sun. The anchor is provided so that the display is properly positioned to allow for real tracking. The parallel rays from the coming from the sun are reflected by the reflector mirror towards the absorber plate via plane mirrors as shown in the Figure.2. The absorber plate is pain ted with black paint to absorb the heat energy to an optimum capacity.

The type of solar cooking box used for experimental analysis is displayed. The solar cooker is made of UV-resistant UV glass. The performance evaluation of a solar cooker's box, the temperature of the suction plate, the temperature of the water in the cooking vessel, and the high and low gloss temperatures need to be measured. To measure the temperature at these points, a thermocouple of the appropriate diameter is installed. Five numbers of thermocouple are necessary for experiment. One thermocouple is inserted in the cooking vessel through a small opening, to measure the food temperature. Two thermocouples are attached to inner and outer glazing of cooker in order to measure the temperature of inner glazing and outer glazing of solar cooker respectively. To measure the ambient temperature one thermocouple is placed outside the solar cooker and the remaining one can be used as per the experiment.

IV. EXPERIMENT USING CONVENTIONAL SOLAR COOKER WITHOUT ANY TES

In case of experiment, the temperatures measured are upper glazing temperature, lower glazing temperature, absorber tray temperature, ambient temperature as well as the food temperature, and the corresponding solar radiation is to be measured using solarimeter.

Table 1 Observation table for temp. at various points of cooker for experiment     without thermal energy storage medium dated on 25/05/2022

The average solar radiation for the whole day was only 639.2 W/m2.

A. Experiment Using Sand As Thermal Energy Storage
During this experiment, the space surrounding the cooking vessel is filled with sand. In this experiment, 4 kg of sand has been used. When compared to the height of cooking vessel, sand level was around three-fourth the height of cooking vessel (as per size of solar cooker and cooking vessel). Solar cooker setup with sand as TES material is shown in Figure 5.

Conclusion

In this project, three set of experiments we performed, which are, 1) Solar cooker without any TES, 2) Solar cooker with water as TES and 3) Solar cooker with sand as TES. a) When the solar cooker with TES and without TES are compared, the maximum temperature is attained for the one with finned absorber plate and the value is 81.3°C, whereas for without TES material, it is 90.6°C. b) The sand gains the temperature faster than the water but it needs to be moisture free. The advantage of using water is that even though there occurs a sudden fall in solar radiation, the water temperature remains the same for a long duration, which is not possible in case of cooker without thermal energy storage. The problem encountered in this experiment was the evaporation and leakage of water and the time for the water ton get heat up. c) As the solar radiation increases, the evaporation of water in absorber tray occurs at a faster rate. Due to imperfections in insulation, water may escape as water vapor, resulting in severe evaporation losses. Also, due to the cooker design imperfections, the water gets escaped through the edges/joints. d) Thermal energy storage materials provide better temperature and reducing cooking time as compared to without TES. Addition of TES materials increases the weight of the solar cooker that makes it heavier, water and sand which are used as TES medium takes time to get heat up.

References

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Copyright

Copyright © 2023 Anand Mohan, Amit Agrawal. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.