Thermal performance assessment of the coaxial pipe evacuated tube solar air heater in Bilaspur climatic conditions

The present era finds the implementation of small-scale solar thermal applications to overcome emissions caused by fossil fuels. In this connection, a forced convection co-axial pipe evacuated tube solar air heater is fabricated and examined under various operating parameters and in Bilaspur Chhattisgarh climatic conditions in the months from October 2021 to March 2022. The performance parameters under consideration were outlet air temperature, collector efficiency, exergy efficiency, and overall system efficiency. The experiments have been performed for different mass flow rates 9.36, 15.84, 18.36, 22.32, and 26.28 kg/h of air. The ambient air temperature varied in the range of 20.8 °C to 41.6 °C. The air temperature at the inlet of the heater varies from 28.4 °C to 66.7 °C. The maximum outlet air temperature and temperature rise recorded were 82.9 °C and 37.2 °C in the month of March and February, respectively, for the low mass flow rate of 9.36 kg/h. It was observed that the maximum collector efficiency, exergy efficiency, and overall system efficiency were achieved as 82.95%, 6.4%, and 81.92%, respectively, for a moderate mass flow rate of 15.84 kg/h. All the performance parameters seem to be strongly dependent on the solar intensity and were found to be highest when the intensity was at its peak value. It is found that the increase in mass flow rates beyond 15.84 kg/h tends to decrease the temperature rise as well as the efficiency of the solar heater. No significant temperature rise is observed for a mass flow rate beyond 26.28 kg/h. The study finds that the fabricated setup can effectively produce a low to moderate temperature range (40 °C–80 °C) and can be used for domestic as well as small-scale industrial applications.