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Experimental and Numerical Investigations of Extended Jet Effects on Multiple-Jet Impingement Heat Transfer Characteristics


 A jet impingement system equipped with extended jet holes was experimentally evaluated in this study. To reproduce a strong crossflow condition, the jet impingement configuration featured a multiple-jet array of 16×5 rows in the streamwise and pitchwise directions, respectively, and the crossflow was exhausted from one open side of the impingement channel only. The transient thermochromic liquid crystal (TLC) technique was used to measure heat transfer on the target surface for different extended lengths of 1.0-2.5 jet hole diameters with Reynolds numbers from 1.0×104 to 3.0×104. To provide complementary flow physics for elaborating the heat transfer patterns observed from the experiments, well-validated numerical simulations were carried out. Comparisons with a baseline jet hole configuration showed that the extended jet holes helped to significantly improve the heat transfer levels as well as to generate a more uniform distribution pattern by suppressing the crossflow. Despite an aerodynamic penalty, the extended jet holes provided much higher heat transfer levels at equal pumping power consumption. The flow fields obtained by the numerical simulations revealed that the jets issued from the extended jet holes were straighter and had less mixing with the crossflow, resulting in a higher jet momentum impinging onto the target. Most importantly, it was found that the dominated flow mechanism of the extended jet holes was to prevent the jets from being redirected by the crossflow in strong crossflow conditions, rather than reducing the jet-to-target distance.