Heat transfer enhancement for turbulent mixed convection in reciprocating channels by various rib installations

This paper numerically studies how the rib-pitch, rib-land, and rib-blockage ratios affect the axisymmetric turbulent flow and heat transfer in a reciprocating circular ribbed channel. The pitch ratio (rib-pitch to rib-height ratio of 8, 11, and 22), land ratio (rib-width to rib-height ratio of 0.5, 1.0, and 2.0), and blockage ratio (rib height to channel diameter of 0.05, 0.1, and 0.2) of rib were changed with a constant Reynolds number (10,000) under various Grashof numbers (∼0-400,000,000) and pulsating numbers (0 and 4.64). The average time-mean Nusselt number in the circular ribbed channel is 94.44-184.65% greater than that in the smooth channel undergoing reciprocating motion. The combined effect between buoyancy, reciprocating force, and inlet fluid momentum enhances the heat transfer from the wall in the channel. The turbulent heat transfer from the wall is improved by increasing land and blockage ratios of ribs with decreasing rib-pitch ratio for the channel.