Impact of load variation on the energy and exergy efficiencies of a single vacuum tube based solar cooker

A single vacuum tube based solar cooker has high energy and exergy efficiency, and is capable of achieving cooking temperatures as high as 250 C. The reason for high energy and exergy efficiencies of this solar cooker is the high achievable concentration ratios of 15e20, which are not possible with multiple vacuum tube based solar cookers. In this paper, a comparative study has been carried out to experimentally determine the impact of varying the load on the various performance measuring parameters. Five experiments have been carried out with 3, 4, 5, 6 and 7 kg of respective water loads. Performance measuring parameters including the energy and exergy efficiencies, heat loss coefficient, quality factor, adjusted quality factor, peak exergy power, and peak exergy power to temperature difference gap product have been determined for each case. It is concluded that the performance measuring parameters have correlation with the load on the solar cooker. Performance parameters indicate average peak exergy power of 51.07 W, while the product of temperature difference gap at half power to that of peak exergy power is about 3000 W K. The highest value of the quality factor was found to be 0.0506 with 6 kg of water load. © 2014 Elsevier Ltd. All rights reserved.