Thermo-hydraulic performance augmentation of solar air duct using modified forms of conical vortex generators

The present work investigates the thermo-hydraulic performance improvement of a solar air duct by deploying modified conical vortex generators (VGs) on the absorber plate heated with uniform heat flux of 1000W/m(2). Half and truncated half conical VGs at six different angle of attacks are considered for numerical simulation at a wide relevant range of Reynolds number varying from 3000 to 15,000. Commercial CFD tool, ANSYS FLUENT is used for simulating eighty four simulations on three dimensional model of VG integrated solar air heater with turbulent flow. RNG k-epsilon turbulent model is employed to solve the complex governing equations of CFD. Results are analysed in detail based on different performance parameters namely Nusselt number (Nu), friction factor (f), thermal enhancement factor (Nu(mod)/Nu(s)), friction factor enhancement factor (f(mod)/f(s)) and thermohydraulic performance parameter (THPP). The modified geometries are found to enhance Nu by about 7% and 4% compared to that of a smooth and conical VG integrated duct respectively. However there is an enhancement of 21% and 16% in local Nu due to the modifications in conical VG. Optimization based on performance at different angle of attack is carried out for both the modified conical VGs. At a higher Reynolds number value, truncated conical VG gives higher value of THPP. A maximum THPP of 1.06 is obtained for half conical VG at an angle of attack of 60 degrees as compared to 1.02 for conical VG. The results are further supported and explained by exploring the temperature field, x-velocity, static pressure, turbulent kinetic energy and helicity contours. Modified conical VG shows a remarkable enhancement in overall performance as compared to conical VG.