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Due to high energy demand and adverse effect of global warming, improving the performance of solar thermal systems is of great importance. In this respect, the transient flow and thermal behavior of turbulent naturally ventilated airflow in a flat plate solar air heater (SAH) are investigated numerically. To achieve this aim, conservation of mass, momentum, and energy equations are solved for the turbulent airflow concurrently with the conduction equation inside the solid element using finite element method (FEM). The low Reynolds turbulence model is applied in the calculation of turbulent stress and heat flux, and the Boussinesq approximation is applied for computing buoyancy forces associated with the density gradient. The surface radiation is also considered explicitly in the calculations to obtain more accurate and reliable results. It is found that although based on the considered location the maximum incident radiation occurs at the optimum angle of 30°, the maximum flow rate reach to its peak when the inclination angle is 60°, in which the total increase of incident radiation is nearly 17%. It is also found that the rate of heat transfer is a decreasing function of the inclination angle ( 30 ⩽ θ ⩽ 90 ), such that the overall rate of heat transfer reduction is around 50%. Further, investigation of the impacts of solar radiation and air duct width on thermal performance showed that by increasing both parameter the rate of heat transfer and air flow increase by about 35% and 100% respectively. The exclusive analysis of the effects of sudden climate change on the SAH’s behavior revealed that a short time climate change leads to zero incident radiation, and considerable fluctuations in outlet temperature and flow rate. |
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