Experimental Investigation of Perforated Glazed Transpired Solar Air Heaters

In this experimental study, performances of a novel type solar air heater, perforated glazed solar air heater (PGSAH), and a black coloured unglazed transpired solar air heater (UTSAH) was surveyed. The current study involves two series of experiments. The first series of experiments are accomplished on single pass perforated glazed solar air heaters (SPGSAHs) with different inner colours which have no absorber plates inside the collectors. The second series of experiments have been carried out on double pass perforated glazed solar air heater with packed beds (DPGSAHPB) which are used as absorber plates. The thermal performances of SPGSAH having different inner collector colours, DPGSAH with packed beds and UTSAH were investigated experimentally in this study. Moreover, in order to compare the performances of the PGSAHs and UTSAH, two PGSAHs having perforated plexiglas glazing were constructed and a UTSAH with black coloured perforated sheet metal utilized as an absorber plate was constructed. The diameters of the holes of plexiglas covers and sheet metal cover were 3 mm and the pitch distance was 30 mm. The fans sucked ambient air into the collectors through the perforated plexi glass in the PGSAHs. The thermal efficiency and outlet temperature of collectors were obtained between various mass flow rates of 0.014 and 0.036 kg/s. It was inferred from results that highest value of thermal efficiency and temperature differences were obtained using green and black PGSAHs in first series of experiments and DPGSAH which utilizes iron wools as packing material in second series of experiments. The results indicated that the thermal efficiencies of UTSAHs were lower than the PGSAHs thermal efficiencies. The maximum values of thermal efficiencies for black, green, blue, red, violet, light yellow and white SPGSAHs are found 85%, 84%, 76%, 65%, 61%, 54% and 55% respectively, at same mass flow rate, the highest thermal efficiency for UTSAH was 50%. Moreover, the average thermal efficiency for DPGSAH with iron wools and DPGSAH with mesh layers are 81.9 %, 75% respectively for air mass flow rate 0.036 kg/s. The highest temperature differences (ΔT) observed were 17.9℃, 17.3℃, 15.4℃ for black, green and blue SPGSAHs respectively for air mass flow rate of 0.024 kg/s. Furthermore, the maximum ΔT for DPGSAH with iron wools is obtained around 29.1℃ at a minimum mass flow rate of 0.014 kg/s. Within specified range of air mass flow rates from 0.014 to 0.036 kg/s, the thermal efficiency of PGSAH enhanced when the air flow rate was increased. As expected, the results demonstrate that thermal efficiencies of PGSAHs were increased if packed bed materials were employed or the collectors were painted by dark colours. The thermal efficiency and outlet air temperature of the DPGSAHPB was greater than the SPGSAH for the same mass flow rates. The DPGSAHPB which utilizes iron wools as packing material had better thermal performance than the DPGSAHPB with mesh layers used as packing material. Keywords: Renewable energy, perforated glazed solar air heater, transpired solar air heater, double pass, thermal efficiency, collector colours