Mathematical Modelling of a Box Type Solar Cooker Incorporating Contact Resistance

Abstract

A solar cooker is a device that uses solar energy to heat food to cook it.  Solar cooking is used to reduce conventional fuel usage and improve the quality of food. Solar cookers have to deal with high concentration heat flows through the contact between metal parts of the absorber plate and the food vessel. For heat transfer, thermal contact resistance plays an important role and it is a major concern to reduce the thermal resistance at the contact. In the present work, mathematical modeling of a lightweight, energy-efficient box-type solar cooker is done by incorporating contact resistance. An experimental setup is developed to find out the thermal contact resistance and thermal contact resistance is evaluated for surface roughness of 0.2 Ra and 0.8 Ra for the Aluminum material. Performance tests of the cooker are carried out to get the figure of merits F₁ and F₂. Also, the load test with the measured thermal contact resistance is carried out with surface roughness of 0.8 and 0.2 Ra. For surface roughness of 0.2 Ra, the % error is observed as 19.77%, 13.69%, 13.68% considering thermal resistance at joints, and −42.89%, 18.95%, and 16.37% without considering thermal resistance at joints. For surface roughness of 0.8 Ra, the deviation is observed as 23.09%, 17.52%, 13.5% considering thermal resistance at joints and −42.89%, 18.95% and16.37% without considering thermal resistance at joints. The figure of merit F₁ is calculated as 0.12 as compared to 0.11 for the commercial cookers, which shows that the newly designed cooker has higher optical efficiency. The figure of merit F₂ is calculated as 0.42 against 0.38 for the commercial cookers. The results thus emphasize that thermal contact resistance is important and should be considered during modeling.