Numerical investigation on the performance of double pass two glazed solar air heaters with jet impingement

Solar air heaters are the simplest heat exchangers for converting solar irradiation into air enthalpy, but their efficiencies are low because the low density and heat capacity of the working fluid. To improve the performance, a new configuration of jet technique is proposed for heat transfer augmentation. The air jet streaks the heated absorber, which leads to extra turbulence and more rate of convection heat transfer.  This technique is examined numerically here for the first time in a two-glazed double pass solar air heater by the Computational fluid dynamics simulation using the COMSOL Multiphysics. The hydrodynamic and thermal behavior of the heater is obtained by numerical solution of the continuity, momentum, and energy equations for both forced and free convection turbulent air flow based on the k–ε turbulence model. Also, the Laplace equation is solved for obtaining the temperature fields in solid elements. The performance of the proposed solar heater is investigated under different incoming solar heat flux and air mass flow rates. A significant increase in thermal efficiency for double pass solar air heaters with jet impinging technique is seen in comparison to conventional solar collectors. The maximum percentages of efficiency increase for the studied test cases are 10% and 6%, corresponding to 0.02 kg/s and 0.04 kg/s air mass flow rates, respectively.