Thermal stratification enhancement in cylindrical and rectangular hot water tanks with truncated cone and pyramid shaped insulation geometry

Abstract

Thermal stratification enhancement in hot water tanks improves the efficiency of solar water heating systems by providing the increase in utilization of the solar energy. In the present study, it was aimed to increase thermal stratification by using truncated cone and pyramid shaped insulation geometry for cylindrical and rectangular hot water tanks. Numerical analyzes were carried out for three parameters and eight hours time interval in the study. These parameters are the tank aspect ratio (D/H), the ratio of the bottom insulation diameter to the top insulation diameter (d(i)/D-i), and the ratio of the bottom insulation thickness to the top insulation thickness (h(b)/ h(t)). Low values of D/H, d(i)/D-i, and h(b)/h(t) ratios reduced the amount of hot and cold water mixture in the tank and increased the thermal stratification. The maximum thermal stratification occurred at D/H = 0,3, d(i)/D-i = 0,75 and h(b)/h(t) = 0,02. For these parameter values, the maximum water temperature difference (Delta T-max) between the bottom and top region of the tank was increased by 131% for the cylindrical tank and 138% for the rectangular tank. Reducing the D/H, d(i)/D-i and h(b)/h(t) ratios significantly increased the thermal stratification, while reducing the exergy efficiency at a negligible level compared to the use of constant insulation thickness. These results reveal that the cylindrical and rectangular hot water tanks coated with truncated cone and pyramid shaped insulation are feasible in terms of thermal stratification enhancement.