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FLOW AND HEAT TRANSFER FOR JET IMPINGEMENT ARRAYS WITH LOCAL EXTRACTION

Andrew J. Onstad
Department of Mechanical Engineering, 488 Escondido Mall, Building 500 Stanford University, Stanford, California, 94305, USA

Terri B. Hoberg
Department of Mechanical Engineering, 488 Escondido Mall, Building 500 Stanford University, Stanford, California, 94305, USA

Christopher J. Elkins
Department of Mechanical Engineering Stanford University 488 Escondido Mall Stanford, California 94305

John K. Eaton
Dept. of Mechanical Engineering Stanford University 488 Panama Mall Stanford, CA 94305 USA

Abstract

Multiple jet impingement cooling systems are preferred over single jets because they offer higher and more uniform mean heat transfer. Unfortunately, multiple jet systems can suffer from crossflow which is the interaction of the spent fluid with downstream jets. The present work examined impingement arrays in which the spent fluid was removed through local extraction holes. Three different impingement arrays were studied all of which had jet-to-jet spacing of Zn/D = 2.34, jet-to-target spacing of H/D = 1.18, and extraction holes in the jet plane. Magnetic Resonance Velocimetry, MRV, is used to measure the mean velocity field in the largest array. Mean heat transfer measurements were carried out as a function of the jet Reynolds number, ReD, on the first array as well as two additional arrays to examine the effect of the extraction area ratio and the geometric scaling. The Nusselt number, NuD, was shown to have the same functional relationship with the Reynolds number for all three arrays. Also, Nusselt number scaling indicates that very large heat transfer coefficients could be obtained with arrays of small jets.