Heat transfer measurements for jet impingement arrays with local extraction

Impingement heat transfer using an array of jets can produce very high average heat transfer coefficients if the jets are closely spaced and if the spent fluid is removed through effusion holes shortly after impingement. This study measured heat transfer for a compact staggered array pattern of impingement jets with an inter-jet spacing of 2.34 jet diameters. Six local effusion holes (deff/djet = 0.6) surrounded each jet so that impinging air was extracted locally through the same plane as the jets. Three scaled models were tested with jet diameters ranging from d = 0.94–8.46 mm, at a total Reynolds number range of Red = 500–10,000. A combined Nu vs. Re correlation of Nud = 0.36 Red0.59 was found for a jet-to-target spacing of 1 jet diameter. Jet-to-target height was varied from 0.44 to 3.97 jet diameters, and increasing jet-to-target spacing was found to decrease average heat transfer in all cases tested. The smaller scale arrays gave higher dimensional heat transfer coefficients as h varied with the −0.41 power of the diameter for fixed jet velocity and jet-to-target spacing. Heat transfer coefficients of nearly 900 W/m2 K were achieved over an 8.5 cm2 area using the smallest scale array. Overall pressure drop coefficients of approximately seven were measured.