EFFECTS OF GAS RADIATION AND ACCELERATED FLOW ON SOLAR HEATER PERFORMANCE

In this paper, the performance enhancement of solar gas heaters is evaluated by taking the advantage of both radiating gas effect and using converged ducts with the accelerated flow. The analyzed solar gas heater includes the glass cover, air gap, absorber, gas channel, bottom plate, and insulation. The inclined position of the bottom plate relative to the absorber provides a converged shape for the duct of the heater. For the free convection airflow inside the air gap and forced convection gas flow in the heater's duct, the CFD-based numerical simulations are carried out by the finite element method via the COMSOL software. Numerical results reveal the positive effect of gas radiation with the fact that in the downstream side of gas flow with a small convection coefficient, the gas accelerated flow with extra turbulence breaks down the thermal boundary layer and augments the convection heat transfer rate. For the studied test cases, 18% and 8% increases in thermal efficiency are observed due to the gas radiation and inclined position of the bottom plate, respectively. Consistency between the obtained numerical findings and experimental data shows the accuracy of the applied numerical method.