Heat Transfer and Flow Characteristics in Rib-/Deflector-Roughened Cooling Channels with Various Configuration Parameters

The present paper deals with a detailed numerical investigation of the turbulent flow inside a stationary rib-/deflector-roughened cooling channel. Various downstream-shaped deflectors including sloping-board deflectors [Cases A1, A2], guide-shaped deflectors [Cases B1, B2], and drop-shaped deflectors [Cases C1, C2] and configuration parameters such as channel aspect ratio (AR=0.5, 1 and 2), and rib-pitch-to-rib-height ratio (P/e=5, 8, and 10) are investigated. The main objective is to design an appropriate deflector to improve the flow characteristics in the wake of the deflectors and guide the flow between two neighboring rib turbulators to enhance the heat transfer performance. A quasi-three-dimensional flow structure, supported by the stream tracer field in some planes, is established to improve and deepen the understanding as well as the analysis of the complex flow field in the rib-/deflector-roughened channels. In addition, the thermal performance corresponding to various rib-pitch-to-rib-height ratios and aspect ratios emphasizes the role of the configuration parameters in the heat transfer and flow resistance performance. The results demonstrate that the deflectors trip the boundary layer and blend the fluid flow, and that the sloping board deflectors contribute to enlarging the turbulence level of the whole cooling channel, more than in the wake region. It is found that Cases A1 and A2 provide the best heat transfer performance, while Case C1 presents the largest thermal enhancement factor Nu/Nu(0)/(f/f(0))(1/3) at high Reynolds number. The wide-aspect-ratio channel with deflectors and large pitch-to-height ratio ribs exhibits much better heat transfer performance.