Experimental investigation of an evacuated tube collector solar air heater with helical inserts

Abstract

This article presents the performance evaluation of an Evacuated Tube Collector solar air heater equipped with Helical Coiled Inserts (ETC-HI). The performance was experimentally examined simultaneously with simple ETC solar air heater at different mass flow rates ranging 0.003–0.015 kg/s. The effect of helically coiled evacuated tube on the outlet temperature, heat gain, thermal efficiency and pressure losses, has been studied under the normal and reversed system operation. The maximum air temperature at the outlet for ETC-HI was observed to be 112.6 °C, whereas average air temperature of 95.5 °C was recorded corresponding to the mass flow rate of 0.003 kg/s. The maximum thermal efficiency value of 70.9% was achieved for ETC-HI solar air heater at a mass flow rate of 0.015 kg/s, whereas, the thermal efficiency for simple ETC solar air heater was 64.5%. In spite of the pressure drop augmentation by 2.45 times, the effective efficiency of ETC-HI was superior as compared to simple ETC without any economic downside. On the grounds of improved thermal and effective efficiency, ETC-HI solar air heater has been observed to be better and yield higher air temperatures as compared to the simple ETC solar air heater.