A study of the self-oscillating jet impingement nozzle

Abstract

In line jets are used throughout industry for drying and heat transfer. A simple modification to an in line jet offers significant enhancement of transport properties. The addition of a collar to an in line jet exit introduces an acoustic standing wave and flow fluctuations that need no external input. The new oscillating jet when used for impingement surface transport was labeled the Self-Oscillating Jet Impingement Nozzle. The objectives of this research were to characterize the gains in heat transfer caused by utilizing this nozzle in contrast to standard non-oscillating jets. The study consisted of flow visualization, acoustic measurements and heat transfer testing for many parameters. The parameters included nozzle length, flow rate, collar length, and nozzle-to-surface spacing. A nozzle was designed using previous research analysis. A method of freezing the oscillating flow structures for visualization was developed. The acoustically driven oscillations issuing from the oscillating nozzle caused enhanced vortex shedding from jet shear layers and higher mixing rates. The turbulence level on the impingement surface was greatly increased and a large amplitude unsteady stagnation point location was introduced. Heat transfer test and acoustic mapping were carried out for all the listed parameters. Correlations for frequency were obtained to predict nozzle frequency performance.