(221c) CFD Modeling of Solar Air Heaters

Solar air heaters have shown a huge interest in the past few years trying to make developments to enhance its overall performance. Such systems are being used in many applications such as crop drying and space heating aiming to get the most benefit of solar energy and to reduce pollution in the environment. Performance of solar air heater is measured by its thermal efficiency and fan power consumption related to the pressure drop. Different aspects could affect the value of the thermal efficiency and pressure drop such as the solar air heater configuration, mass flow rate, mean velocity of air, solar radiation intensity. It was planned to model solar collectors through Computational Fluid Dynamics (CFD) approach using COMSOL Multiphysics software to investigate the effects of these aspects on the system performance. In terms of configuration, the solar air heater modelled was a double pass single flow with U-turn type in which its depth of flow and U-turn spacing has been studied against the thermal performance and pressure drop. The optimum values of performance parameters were found to be corresponding to 0.01 depth of flow and U-turn spacing where thermal efficiency and pressure drop found to be 47.25% and 93.55 respectively. The effect of the mass flow rate and mean velocity on the performance parameters studied by varying Reynolds number at different ambient temperatures which demonstrated a significant increase of thermal efficiency and pressure drop. At 15000 Reynolds number and 273.15 ambient temperature, the thermal efficiency and fan power consumption were 57.99% and 56.36 respectively. An increase in the solar radiation intensity resulted in increasing the temperatures of both absorbing plates and the mean temperature of air. Higher temperatures were related to the aluminium absorber due to the assumption of non-participating fluid and ultra-clear glass cover resulting in a direct exposure of solar radiation. It also influenced the outlet air temperature by increasing it for a total of 12.69 degrees.