Design and simulation of a solar powered clay refrigerator

Abstract

A solar powered clay refrigerator is designed and simulated with the objective of increasing shelf life of stored vegetables and fruits, in this case tomatoes. Evaporative cooling is dependent on the air temperature, relative humidity, air velocity and thermal conductivity of media. The higher the temperature the higher the evaporation rate thus speeding up the rate of cooling. It is shown that the lower the relative humidity the lower the wet bulb temperature which is the theoretical temperature in the inner clay cabinet. The literature review covers the different types of evaporative cooling and refrigeration methods such as direct and indirect evaporative cooling. The clay refrigerator is designed using solid edge software. Heat and mass transfer analysis which aids in the simulation of evaporative cooling process in the clay refrigerator is done based on Reynolds flow hypotheses. The model proposed herein assumes that the heat transfer due to natural convection is coupled with an imaginary ambient air mass flow rate (gAo) which is an essential assumption in order to arrive at the solution for the rate of water evaporation. Effect of several parameters on the pot-in-pot system performance has been studied. The equations are iteratively solved and detailed results are presented to evaluate the cooling performance with respect to various parameters: ambient temperature, relative humidity (RH), pot height, total heat load and hydraulic conductivity. It was found that pot height and total heat load play a critical role in the performance of the system. Model predicts that the temperature difference can reach a maximum of close to 25 oC for ambient conditions of 50 oC and 10% RH, while minimum temperature difference could be seen close to 2.74 oC for ambient conditions of 30 oC and 50% RH. Thereby verifying the usual concept that evaporative cooling is best suited for hot and dry ambient conditions