Optimization of the air gap spacing in a solar water heater with double glass cover

Abstract

A parametric study has been conducted in a solar water heater with double glass cover, in order to minimize heat losses. The air gap spacing between the absorber and the inner glass cover (L1) and between the two glass covers (L2) for the system with 0.7 m x 1.35 m absorber area were varied within the range of 15-50 mm to investigate which combination of gap sizes (L1, L2) would result in minimum total heat losses i.e. including radiation and convection losses. Three-dimensional CFD models have been developed using ANSYS 13.0-FLUENT software. The continuity, momentum and energy equations have been solved, in steady state condition, using pressure-based type solver. A realizable k-є turbulent model has been used, and surface to surface radiation was included. The results showed that as the size of the air gap increases, the velocity of the air in the gap increases which increased the convection part however the total heat losses decreased. The optimum combinations for the present case have been found to be 40, 25 mm, since the overall heat loss was found to be the lowest (216.4 W).