Abstract
A flat plate solar air collector is a simple energy conversion system with relatively poor performance due to low heat transfer between air and absorber. Passive heat transfer enhancement methods increase the absorber-side contact area and the localized air turbulence. This research article introduces a dual-purpose copper tube as an extended absorber surface as well as heat storage. The absorber designs are spiral coiled and straight tubes with uniform spacing, filled with glycerol and commercial grade paraffin. Thermal and exergy efficiencies of modified solar air heater configurations are compared with conventional collector with a plain absorber without energy storage. The experimental results show that the double-pass solar collector with a spiral tube with paraffin wax has higher thermal performance than the straight tube and conventional collectors. The spiral coil's thermal and exergy efficiencies with paraffin wax are 29.86% and 1.11%, respectively, at an airflow rate of 0.0076 kg/s with a maximum attained air temperature of 59 °C. The air temperature is maintained for a short time in the heat storage-based absorber even after sunset. Thus, the integration of thermal storage into the solar collector stores the heat for off-sunshine hours and enhances the absorber's energy storage capacity and uniform temperature. The modified absorber surface with heat storage results in better performance without auxiliary power. Further, the enviro-economic study ensures a lower payback period for PCM-integrated spiral tube collectors of about 2.4 years. Such simple and economic absorber designs are beneficial to various solar drying and space heating applications.
Published Version
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