Performance analysis of triple-pass solar air heater system: Effects of adding a net of tubes below absorber surface

In this article, two triple-pass solar air heater (TPSAH) collectors have been experimentally investigated to analyse their performances through adding a net of tubes below the absorber surface and double glass cover on one of them for purpose of comparison. The first collector (TPSAH-1) has been covered with a single glass, whereas the second collector (TPSAH-2) has been covered with a double glass and adding a net of tubes below the absorber surface. The experiments for each system have been carried out in winter and compared under the same weather conditions. For all air mass flowrates, the results indicated that TPSAH-2 produces a higher efficiency as compared to TPSAH-1, where the maximum efficiency for high air mass flowrate have been obtained equal to 80.2% and 73.4%, respectively. A considerable temperature difference has been observed when using TPSAH-2 in comparison with that obtained using TPSAH-1. The improvement in the efficiency of TPSAH-2 compared to TPSAH-1 confirms that the adding of a net of tubes and additional glass cover have significant influence on heat transfer rate. The air mass flowrate has a substantially impact as compared to temperature difference. Thus, the performance of TPSAH is directly proportional to rise in air mass flowrate. For TPSAH-1, the glass, plate and outlet temperatures have been always found lower than TPSAH-2. Based on the outlet air temperature, it can be concluded that TPSAH-2 can be used for the applications that required large temperature difference and TPSAH-1 for the applications that required small temperature difference.