Experimental and numerical investigation of impingement heat transfer on a flat and micro-rib roughened plate with different crossflow schemes

Abstract

A combined experimental and numerical investigation of the heat transfer characteristics within an array of impingement jets on a flat and micro-rib roughened plate has been conducted. The experiments are carried out in a perspex model using a transient liquid crystal method. Local jet temperatures are measured at several positions on the impingement plate to account for an exact evaluation of the heat transfer coefficient. The effects of variation of jet-to-plate spacing, crossflow schemes and jet Reynolds number on the distribution of the local Nusselt number and the related pressure loss are investigated experimentally. The jet-to-plate spacing H/ d = 3 results in the highest heat transfer coefficients for both the flat and the micro-rib roughened plate. Overall heat transfer performance on the micro-rib roughened plate is always best for the minimum crossflow case. The heat transfer enhancement ratio increases with increasing Reynolds numbers. All the data from the micro-rib roughened plate is compared to that of the flat plate. The measurements are complemented by a numerical part, in which one particular case from the experiments is investigated by means of a commercial Computational Fluid Dynamics (CFD) software package. In the numerical results, for the heat transfer pattern the same trend as in the experiments is found. In the comparison of local heat transfer coefficients, results from experiments and predictions are of the same order. Significantly more local details are captured in the CFD analysis. The numerical study also addresses and compares the effects of 1D and 3D heat transfer by accounting for the solid domain of the rib material (conjugate heat transfer). The results of the latter show that the CFD predictions can be regarded as a valuable complement to experimental measurements for configurations where heat transfer on rib roughened surfaces are to be evaluated.