Enhanced impingement heat transfer using a Self-Oscillating Jet Impingement Nozzle array

Abstract

A simple modification to an in-line jet (ILJ) has been proven to significantly increase its heat transfer capabilities. The transport properties of the ILJ were enhanced by the addition of a collar over the nozzle exit. When extended to the proper length, the collar will create an acoustic standing wave and flow oscillations at the nozzle exit. The modified impinging jet nozzle has been labeled the Self-Oscillating Jet Impingement Nozzle (SOJIN). The experiments were conducted utilizing air jets submerged in the laboratory's ambient air. An infrared camera was used to measure the temperature distribution of the impingement surface under various operating conditions. Local and average heat transfer coefficients and Nusselt numbers were determined. The research involved two 0.635 cm inside diameter SOJIN nozzles. The study consisted of acoustic measurements and heat transfer testing conducted at Reynolds numbers of 60,000, 100,000, and 140,000. Infrared imaging was used to identify highly, semi, weakly, and non-interactive regions. The optimum first stage collar extensions were found to be 3.6 mm for the 60,000 and 100,000 Reynolds numbers, and 4.1 mm for the 140,000 Reynolds number. An arrayto-surface spacing of 4 diameters was found to be the optimum height for heat transfer purposes. The 60,000 Reynolds number produced average surface heat transfer coefficientsof 1030, 660, 470, and 345 W/m' K at nozzle separation distance-to-diameter ratios, S/D,of 3, 8, 13, and 18, respectively. Each S/D value correspond to the highly, semi, weakly, and non interactive regions, respectively. The S/D value investigated with a Reynolds number of 100,000 were 3, 8, 9, 10, 16 and 24 at H/D of 4. Each fell within the following regions: 3 highly; 8, 9, 10 semi; 16 weakly; and 24 non-interactive. The average surface heat transfer coefficients were determined to be 790, 850, 665, 490, and 350 W/m' K, at S/D of 3, 8, 9, 10, 16, and 24, respectively. The 140,000 produced the highest heat transfer coefficients. The average surface heat transfer coefficients were 2030, 1580, 890, 625, and 470 W/M2 K, for S/D of 3, 6, 14, 21, and 25, respectively. The maximum local heat transfer values showed small changes with respect to nozzle separation distance.