Effect of artificial roughness on flow and heat transfer of transcritical methane

Abstract

This study performed 3D steady-state simulations of the flow and heat transfer of transcritical methane in a rectangular channel with and without artificial roughness under asymmetric heating conditions. The effect of artificial roughness with different rib height and pitch on the results was analyzed. The simulation results demonstrate that the artificial roughness disturbs the flow field near the ribs severely. With the increase of the rib height, the temperature of the coolant near the bottom increases gradually due to enhanced heat transfer, which results in the core region of the flow moving towards the upper surface of the channel. In addition, the presence of artificial roughness smoothens the transcritical process, and deteriorates the hindrance of heat transfer between fluids due to the extreme value of specific heat near the pseudo-critical temperature. This suppresses the deterioration of heat transfer, reduces the peak wall temperature, and moves it downstream. However, the addition of artificial roughness can significantly increase the pressure loss, which can be further enhanced by increasing the rib height or reducing the rib pitch. The overall performance of artificial roughness is evaluated by the thermal performance factor, which takes both the heat transfer enhancement and pressure loss into consideration. Based on this parameter, the best comprehensive performance can be obtained for a rib height of 0.3 mm and a rib pitch of 5 mm under the cases adopted in this paper.