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International Heat Transfer Conference 12

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

Heat Transfer Between an Under-expanded Jet and Plane and Cylindrical Surfaces

Ieuan Owen
Heat and Mass Transfer Laboratory, Department of Mechanical Engineering The University of Liverpool, P.O. Box 147, Liverpool, L69 3BX, U.K.

Mostafa Rahimi
Department of Engineering The University of Liverpool Liverpool, L69 3GH, UK

John Mistry
Department of Engineering The University of Liverpool Liverpool, L69 3GH, UK

DOI: 10.1615/IHTC12.3030
6 pages

要約

This paper presents a selection of data from an investigation that was concerned with the heat transfer that occurs when an underexpanded jet impinges onto heated plane and cylindrical surfaces. The purpose of the study was to establish the thermal boundary conditions for calculating thermal stresses in heat transfer surfaces when subjected to high-speed cleaning jets. The heat transfer in the impingement zone of a high-speed jet is extremely high and when the surface interferes with the expansion of the jet, the radial and circumferential distributions of the heat transfer coefficient become complicated. If a highly under-expanded jet impinges upon the surface while the nozzle-to-surface spacing is small, z/D ~ 3, there is no longer a maximum stagnation heat transfer coefficient on the geometric axis of the jet, instead a stagnation 'ring' is formed with a radius of about one nozzle diameter. Experimental results are presented for a convergent nozzle of 12.7 mm diameter supplied with air at pressure ratios up to 5.08, and nozzle-to-surface spacings of 3, 6 and 10 nozzle diameters. In addition to the measured data, a clear outcome of the work is that the usual method of representing Nusselt number as a function of Reynolds number is inadequate in compressible flows where the dimensional analysis shows that the nozzle Mach number, or pressure ratio, should also be included.

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