Characterisation of edible sunflower as a heat storage medium for solar cooking

Abstract

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.

Charging and discharging experiments to evaluate Sunflower Oil as a heat storage medium for domestic solar cooking applications are presented. An experimental setup to evaluate the thermal performance of Sunflower Oil during charging and discharging cycles is presented. Energy and exergy based experimental thermal performance parameters are evaluated. Energy, exergy, thermal gradient and exergy factor values are evaluated with experimental tests. High temperature charging is found to be the most viable option. This option results in higher energies, higher exergies, higher thermal gradients and higher exergy factors. For the discharging cycles, a high flow-rate results in a fast heat transfer rate. This fast rate of heat transfer destroys thermal stratification earlier but heats up water faster. The lower discharging flow-rate ensures that the discharging cycle can be carried out for a longer period. This is beneficial in utilizing the stored energy and exergy for a longer period, such that it can be used for cooking foods that take a longer time to cook. An optimal discharging flow-rate is also suggested. The optimal flow-rate comprises between fast heat transfer and using the stored energy more effectively. Exergy factor profiles during charging and discharging cycles show characteristic dips which correspond to the time when the thermal gradients begin to decrease. Sunflower Oil is found to be a viable and readily available TES medium which can be used in domestic solar cooking applications.