Energy and Exergy Analyses of Plastic Solar Air Heater Developed from Chlorinated Polyvinyl Chloride Pipes

Abstract

The solar air heaters fabricated from plastics could reduce both material and fabrication costs. However, those fabricated from conventional plastics such as PVC suffer from the fundamental drawback that they cannot withstand higher temperatures. This work aims at fabricating a plastic solar air heater (PSAH) using chlorinated poly vinyl chloride (CPVC) and experimentally investigating its performance with cover made of 0.5 mm thick polyethylene and that without cover. To examine the effectiveness of PSAH at a tilt angle of 30°, all investigations were carried out at the University campus of Manipal, Dubai (25°08′00.1″ 55°25′31.0″ E) at an average global solar irradiation of 290 W/m²and average ambient temperature of 33–37.7°C from April16 to May 20, independently, for the two situations: with and without covers. The temperature rise of the air was recorded in both the inlet and outflow at different intervals by adjusting the MFRs of the air in steps of 0.025 kg/s, ranging from 0.02 to 0.055 kg/s. Energy efficiency (η_energy), exergy efficiency (η_exergy) of the collector, coefficient of hydraulic resistance, pressure drop, heat loss factor and thermal and optical heat losses were evaluated at various mass flow rates (MFR) of air as well as with the time of the day. It was found that the highest collector’s η_energy is found as 30 and 70.6% respectively for PSAH without cover and with cover with a constant inflow of air at 0.05 kg/s while the highest η_exergy is observed to be 17.8 and 26.1% respectively at an MFR of 0.03 kg/s. Collector’s η_energy increases with an increase in MFR of air while η_exergy shows the reverse trend. The highest rise in temperature of air was found to be 14.5 and 44^oC for PSAH without and with covers respectively. The coefficient of hydraulic resistance and pressure drop were observed to be insignificant. The overall heat loss coefficient for convection is calculated for PSAH without and with top covers respectively to be 3.7 and 2.4 W/m² K. The maximum rates of thermal and optical losses were also calculated for PSAH without and with top covers to be 140, 75 W and 102 and 42 W respectively. Thus, the useful energy without and with top covers is 38 and 59% respectively of the total energy supplied by the PSAH (345 W).