Thermal performance of a solar box cooker with forced convection heating and sensible heat storage
Abstract
A solar box cooker using a 12 V DC fan in the forced convection mode is experimentally evaluated. The experimental tests use two black stainless steel cooking pots with and without storage. The storage system consists of a glass bowl with 500 g of granite, and one pot is placed inside the glass bowl. The experimental tests are carried out for a 10-hour interval. The first part of the experiments involves testing without any load for 4 hrs to establish the stagnation temperatures. The second part of the experiment consists of loading the cooking pots with 1 litre of water for 6 hrs. The pots with and without storage are tested simultaneously in the solar cooker. Experimental results without the fan blowing and without the load show that the highest temperatures for the storage and non-storage cases are around 142 and 123 oC, respectively. For the case of forced convection using the fan without the load, the corresponding maximum temperatures in the cooking pots are around 156 and 135 oC, respectively. During the 6 hrs water heating cycle, maximum temperatures attained for the storage and non-storage cases are 92 and 81 oC without the fan. These maximum temperatures are comparable to the forced convection maximum temperatures of 93 and 82 oC, achieved at about the same time. The first figure of merits (F1) for the storage case with and without the fan of 0.121 and 0.110 oC/Wm2 is greater than those of the non-storage case of 0.102 and 0.092 oC/Wm2, respectively. Using the fan results in an improvement of the first figure of merit. The storage case shows better performance in terms of the higher cooking temperatures achieved and the higher first figure of merits; however, there is no advantage to using forced convection when the pots are loaded after achieving higher temperatures in the no-load tests.