Thermal performance evaluation of solar air heater using combined square and equilateral triangular rib roughness

ABSTRACTHeat transfer and fluid flow characteristics in roughened solar air heater duct with combined square and equilateral triangular ribs as roughness is investigated using experimental and computational fluid dynamics (CFD) approaches. Relative roughness pitch (7.14 ≤ P/e ≤ 17.86), roughness height (e/D = 0.042), Reynolds number (3800≤ Re ≤ 18,000) and heat flux (1000 W/m2) are used as operating parameters. Turbulent flow is simulated using ANSYS FLUENT code with RNG k-ɛ turbulence model. The vortices generated around the ribs and grooves are considered to be responsible for the enhancement in heat transfer rate. Thermo hydraulic performance parameter (THPP) has been evaluated for optimum configuration of the roughness element for given set of geometrical and operating parameters. A value of 1.86 has been recorded as an optimum value of THPP for the range of parameters investigated. Solar air heater with combined ribs shows better performance when compared with the individual rib performances.