Optimization of tube arrangement and phase change material for enhanced performance of solar air heater- A numerical analysis

Abstract

Application of Solar Air Heater (SAH) could be extended to off sunshine hours by integrating SAH with a Thermal Energy Storage System (TESS). Design optimization of TESS will enhance thermal performance of SAH integrated with TESS. Mass flow rate and inlet temperature of air, type of Phase Change Material (PCM), alignment and dimensions of tubes in TESS play an important role in its design optimization. In the present study, numerical analysis using ANSYS FLUENT was carried out to optimize the design of TESS. Mass flow rate of air in terms of velocity at the inlet was changed from 3.5 m/s to 5.5 m/s in a step of 0.5 m/s. Three different PCMs including paraffin wax, n-octadecane, calciumchloride hexahydrate (CaCl2•6H2O) were considered. Inline, staggered and circular arrangement of tubes were considered in the TESS. Temperature of air at inlet to TESS is changed to 40 °C, 50 °C, 60 °C, 75 °C, 100 °C and 125 °C. Results are obtained in terms of average tube wall temperature, average PCM temperature in tubes, average surface heat transfer coefficient and average heat absorbed by PCM. Tubes in staggered arrangement increased heat absorbed by PCM by 10.45% and 48.03% respectively with paraffin wax and CaCl2•6H2O as PCM compared to tubes in inline arrangement. There is insignificant improvement (0.09%) between staggered and inline grid arrangements when n-octadecane was used as PCM. Tubes in circular arrangement increased heat absorbed by PCM by 9.17%, 1.55% and 1.08% respectively with paraffin wax, n-octadecane and CaCl2•6H2O as PCM compared to tubes in staggered arrangement. Similarly, it increased heat absorbed by PCM by 17.89%, 1.63% and 48.59% respectively compared to tubes in inline arrangement.