Numerical Investigation of the Turbulent Flow and Heat Transfer around a Heated Cube Cooled by an Impinging Jet in a Cross-Flow

Abstract: Impinging jets are used for many industrial applications where high heat and mass transfer rates are required. The electronic industry is one of the fastest growing industries and applications of cooling technology in this field are of considerable importance. Forced channel flow is frequently used as a cooling technique. In combating the whole thermal load with forced channel flow, excessive flow rates will be required. The typical electronic system contains one or a few high heat–dissipating components. One possible method to face this problem is to divide the channel flow into an impinging jet and a low-velocity cross-flow. The impinging jet is placed over the high heat-dissipating component and provides a local region with high cooling performance, especially at the stagnation point. The cross-flow is important to insure that well-distributed cooling performance is provided at the remaining part of the electronic system, which requires less cooling.Impinging jets are also of great scientific interest. Extensive experimental and numerical research has been carried out to predict the flow and heat transfer characteristics in the stagnation region of an impinging jet where most of the investigations have been focused on axi–symmetric round impinging jets without any cross-flow.The purpose of this study is to examine a spot cooling technique consisting of en impinging jet in combination with a low-velocity cross-flow by use of CFD. The cases are limited to a heated wall-mounted cube with different height which is placed in a channel with different heights and cooled by an impinging jet and a cross-flow with different velocities. The study can be divided into three parts: a verification study, a detailed study and a parametric study.The verification part consists of a verification of two steady-state Reynolds-Averaged Navier-Stokes turbulence models, a v2-f model and a Reynolds Stress Model (RSM). The results show that both models predicted similar results in the near-wall region except in the stagnation region from the impinging jet where the wall-normal turbulent Reynolds stresses and the turbulent kinetic energy where significantly higher in the RSM than in the v2-f model and in the measurements. The general trend was that the predicted surface temperature and the mean velocity field in the free shear-flow, i.e. far from the walls, from the RSM was in better agreement with the measurements than the results from the v2-f model.The detailed study presents an unsteady simulation by use of Large Eddy Simulation (LES) for a case identical to the verification study in order to predict the time-averaged velocity field, the turbulence characteristics and the heat transfer rate. The agreements between the results from the LES and the measurements were in general improved compared with the RSM and the v2-f model especially in the stagnation region from the impinging jet.The parametric study is carried out by use of the validated RSM where influence of the velocities of the impinging jet and the cross-flow, the distance between the top and bottom plates, and the height of the cube on the heat transfer rate and on the pressure drops was investigated.