A numerical investigation of square sectioned transverse rib roughened solar air heater

摘要

The use of artificial roughness in the form of repeated ribs on a surface is an effective technique to enhance the rate of heat transfer. A numerical investigation on the heat transfer and fluid flow characteristics of fully developed turbulent flow in a rectangular duct having repeated transverse square sectioned rib roughness on the absorber plate has been carried out. The commercial finite-volume CFD code ANSYS FLUENT (ver. 12.1) is used to simulate turbulent airflow through artificially roughened solar air heater. The Navier-Stokes equations and the energy equation are solved in conjunction with a low Reynolds number RNG k-ε turbulence model. Twelve different configurations of square sectioned rib (P/e = 7.14-35.71 and e/D = 0.021-0.042) have been considered. The flow Reynolds number of the duct varied in the range of 3800-18,000, most suitable for solar air heater. The effects of relative roughness pitch and relative roughness height on Nusselt number and friction factor have been discussed and the results are compared with the square sectioned rib roughened duct and smooth duct under similar flow conditions to investigate the enhancement in Nusselt number and friction factor. Roughness and flow parameters for artificially roughened solar air heater have been optimized by considering the thermo-hydraulic performance parameter based on constant pumping power requirement. It has been found that the square sectioned transverse rib roughened duct with P/e = 10.71 and e/D = 0.042 offers the best thermo-hydraulic performance parameter for the investigated range of parameters.