On the solar air heater thermal enhancement and flow topology using differently shaped ribs combined with delta-winglet vortex generators

A numerical investigation has been conducted to study the convective heat transfer enhancement and friction loss behaviors for turbulent flow by using arrays of differently shaped ribs combined with delta-winglet vortex generators (DWVGs) pair on the absorber plate of a solar air heater. Four transverse vortex generators arrays, i.e., 90° continuous ribs, 90° truncated ribs, 60° V-shaped continuous ribs, and 60° V-shaped truncated ribs, are studied to investigate the mixing effect with the DWVGs pair. The aspect ratio (AR = L_v/H_v) of the DWVGs is 2:1 while the geometrical condition of the ribs is height of 0.003 m and pitch of 0.028 m. The Reynolds number ranges from 4000 to 20,000. Results of temperature, Nusselt number, vortical structure, topological portrait, turbulent kinetic energy (TKE), friction factor and thermal performance evaluation are included. The results show that the adoption of DWVGs and the shape type of the ribs have great impact on the heat transfer and flow structure in the solar air heater. It is found that the DWVGs combined with the 60° V-shaped continuous ribs contributes the best heat transfer performance, and the heat transfer is enhanced by 39.4% compared with the only DWVGs case.