Effects of Microribs on the Thermal Behavior of Transcritical n-Decane in Asymmetric Heated Rectangular Mini-Channels Under Near Critical Pressure

Abstract

Microrib is a very promising heat transfer enhancement method for the design of scramjet regenerative cooling channels. In this paper, a three-dimensional numerical model has been built and validated to parametrically investigate the thermal behavior of transcritical n-Decane in mini cooling channels with microribs under near critical pressure. The results have shown that the height and pitch of microrib perform a nonmonotonic effect on the convective heat transfer coefficient of n-Decane inside the cooling channel and the optimal microrib parameters stay at low values due to dramatic changes of coolant thermophysical properties in the near critical region. Due to severe thermal stratification and near critical conditions, there will be a significant recirculation zone in vertical direction near microrib, and its interaction with the strong secondary flow in axial direction caused by limited channel width of mini-channel will largely enhance the local convective heat transfer and its downstream region. Besides, the dramatically changing thermophysical properties of n-Decane will lead to a locally remarkable heat transfer enhancement phenomenon similar to impingement cooling at the front edge of microribs.