Performance analysis of a double-pass solar air heater system with asymmetric channel flow passages

Abstract

The present work seeks to address the forced convection heat transfer behaviour of a double-pass solar air heater system (DPSAHS) provided with asymmetric channel flow configuration used for solar drying of agro-products. Outdoor experiments were performed on a DPSAHS having a constant channel depth ratio of 1.5. Thermal response of the DPSAHS under different influencing parameters such as flow rate, channel depth, and thermophysical properties of the working fluid was experimentally determined. The influence of ambient parameters such as solar intensity, ambient temperature, wind speed, and relative humidity on the thermodynamic behaviour of the DPSAHS was also investigated. Among which, solar intensity and ambient temperature were found to be the major parameters influencing the energy and exergy efficiency followed by wind speed. Relative humidity was found to have the least percentage contribution towards the thermal characteristics of the system. Overall thermal efficiency and exergy efficiency were found to vary in the range of 20–41% and 5.6–18% at two different mass flow rates of 0.02 kg s−1 and 0.03 kg s−1, respectively. The results also inferred that the influence of thermophysical property variation on the thermodynamic performance depends upon the operating temperature range and on the nature of working fluid. Air temperature in the lower channel was found to be an average 3 °C higher than that of upper channel passage corresponding to two different mass flow rates. Hence, the thermodynamic behaviour of DPSAHS was found to be strongly influenced by the variation in channel depth, ambient parameters, and mass flow rate. The obtained experimental results were also compared with the available literatures.