Numerical investigation of heat transfer and fluid flow in a solar air heater duct with multi V-shaped ribs on the absorber plate

A numerical investigation of heat transfer and fluid flow characteristics in a solar air heater duct having multi V-shaped ribs on the absorber plate is presented in this study. Three-dimensional simulations are conducted using the ANSYS FLUENT code and the Renormalization-group k-ε turbulence model. The computations are performed for different rib geometries with a varying spanwise V-rib number, relative rib pitch, relative rib height, and angle of attack, and for different Reynolds numbers. The effects of the rib geometrical parameters on the Nusselt number, friction factor, and flow structure are obtained and analyzed. Clearly, the multi V-shaped ribs greatly enhanced the heat transfer. The maximum value of the thermal performance parameter was found to be 1.93 for the range of parameters investigated. The multi V-shaped ribs generate streamwise helical vortex flows, which promote the fluid mixing between the colder mainstream fluid and the warmer fluid near the absorber wall. In addition, the moving subsidiary vortex structure at the inter-rib region further enhances the local fluid mixing.