Annals of the Assembly for International Heat Transfer Conference 13

ISBN 1-56700-225-0 / CD 1-56700-226-9

Year 2006

W. Liewkongsataporn
Georgia Institute of Technology, Atlanta, USA

F. Ahrens
Georgia Institute of Technology, Atlanta, USA

T. Patterson
Georgia Institute of Technology, Atlanta, USA

This paper reports the results of a numerical study of impingement heat transfer enhancement via pulsating jets produced, e.g., by a pulse combustor, compared to heat transfer with steady jets. The main objective is to determine enhancement factors, in terms of net heat flux, for impingement drying applications. Another objective is to preliminarily investigate the mechanisms of enhancement. The study is based on CFD simulation using the commercial software FLUENT. Reynolds numbers of pulsating and steady jets are 7,800 based on tailpipe diameter and evaluated at the inlet temperature. Two parameters are varied, i.e., H/D from 1 to 4, and amplitude ratio from 2 to 10. Results show that pulsating heat transfer increases with increasing amplitude ratio. The degree of enhancement also depends on the area over which the heat flux is averaged and the nozzle-to-surface distance. The enhancement (or reduction) of impingement heat transfer depends on whether the heat flux during positive cycle of oscillation is great enough to compensate the much lower heat flux during negative cycle. The simulation predicts the existence of a coherent structure, or toroidal vortex, with pulsating jets. It is also found that ambient air drawn into the tailpipe (nozzle) during flow reversal significantly affects the mean temperature of the pulsating jets.

JET-14 pages DOI: 10.1615/IHTC13.p16.130 Download article

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