Thermal performance improvement of the modified evacuated U-tube solar collector using hybrid storage materials and low-cost concentrators

Abstract

Abstract This study aims to enhance the thermal performance of an evacuated tube solar water collector. To experimental investigate this idea, a modified evacuated U-tube solar water collector with hybrid storage materials and low-cost cylindrical parabolic concentrators were designed, constructed, and tested in Tanta city under the Egyptian weather conditions. To investigate the influences of the graphite powder mass concentration within hybrid energy storage material on thermal performance of the modified evacuated U-tube solar water collector with low cost cylindrical parabolic concentrators. Five different mass concentrations of graphite nanoparticles in hybrid storage materials (0.0, 2, 3, 4, and 5% by weight) was studied and compared to the case without hybrid energy storage material to obtain influences of hybrid storage materials with different mass concentrations on the thermal performance of the modified design. The results show that with increasing the rate of feed water from 14 to 22 LPH during the period 10:00 am-10:00 pm, the sum of the useful heat gain produced from the modified design with hybrid storage materials varying between 17,133 and 20,146, 17,458 and 20,378, 17,665 and 20,796, 17,783 and 20,954, 17,960 and 21,075 kJ/day at 0.0, 2, 3, 4, and 5% graphite mass concentration, respectively. But for the operating case without hybrid storage materials, the sum of useful heat gain varying between 10,605 and 12,255 kJ/day. The results of this study presented that, the average improvement in the sum of useful heat gain for the modified design with hybrid energy storage material reached 63.5, 65.8, 68.7, 69.9, and 71.1% at 0.0, 2, 3, 4, and 5% mass concentration, respectively compared to cases without storage material. Also, with increasing the mass concentration of graphite in hybrid storage material from 0.0 to 5%, the improvement in the daily thermal efficiency of the modified design reached to 69.4%, 72%, and 72.1% for the rate of feed water 14, 18, and 22 LPH, respectively as compared to the cases without hybrid storage material.