An experimental investigation of a double pass solar air heater performance: A comparison between natural and forced air circulation processes

This work involves an experimental study on a trapezoidal Double-Pass Solar Air Heater (DPSAH) to analyse its performance under natural and forced convection cases for the purpose of comparison. The experiments have been conducted in winter and compared for each case in same time and weather conditions. The collector has been carefully designed and constructed to prevent as possible the heat losses. A uniform fins have been fixed on both sides of the absorber plate to enhance the heat exchange rate. Effects of solar radiation and air mass flowrate on DPSAH performance have been investigated. The results show that DPSAH produces higher efficiency when the system is operated under natural convection case in comparison to forced convection case. The maximum efficiency has been found equal to 73.5% and 65% for natural and forced convection, respectively. A significant temperature difference has been obtained under natural convection case compared to forced convection. The results confirmed that DPSAH with adding fins leads to considerable performance improvement compared to conventional DPSAH due to enhance the absorbing solar energy caused by increasing surface area. The increasing in air mass flowrate has inverse influence on the performance of DPSAH. For natural circulation case, the outlet, plate and glass temperatures have been always observed higher than the forced convection case. It is evident that type of heat transfer has considerably affect the system performance and consequently, the selection of air circulation process are required to be satisfactorily chosen according to the application to achieve the desired objective.