High Pressure Spray Cooling of a Moving Surface

[+] Author and Article Information
G. G. Nasr

Head of Spray Research Group (SRG), Institute of Materials Research (IMR), School of Computing, Science and Engineering,  University of Salford, Manchester M5 4WT, UKg.g.nasr@salford.ac.uk

R. A. Sharief, A. J. Yule

Department of Mechanical, Aerospace and Manufacturing Engineering,  UMIST, P.O. Box 88, Manchester M60 1QD, UK

J. Heat Transfer 128(8), 752-760 (Jun 24, 2005) (9 pages) doi:10.1115/1.2217747 History: Received May 13, 2003; Revised June 24, 2005

A novel technique is described for investigating spray cooling of moving hot surfaces. An experimental investigation is described for vertically downwards water sprays impinging on a horizontal steel annulus of 250mm diameter with a surface temperature up to 600°C, and rotating at up to 120rpm, giving a tangential velocity of 1.35ms1. The central homogeneous zones of sprays from full-cone atomizers are used at pressures up to 2.07MPa and the ranges of impacting spray parameters are 0.98to12.5kgm2s1 for mass flux, 49230μm for volume median drop diameter, and 9.832.3ms1 for impinging velocity (Yule, A. J., Sharief, R. A., and Nasr, G. G., 2000, “The Performance Characteristics of Solid Cone Spray Pressure Swirl Atomizers  ,” Ann. Tokyo Astron. Obs., 10(6), pp. 627–646). Time histories of the steel temperature, at positions within the annulus, are presented and analyzed to deduce the transient cooling as the instrumented section of the annulus was swept repeatedly under the spray. Discussion is provided on the physical processes occurring on the basis of the observations. Correlation equations derived to find relationships of surface heat flux with the spray and surface parameters provide further insight into these processes. The results confirm results for static surfaces, that droplet size is a relatively weak parameter, while droplet momentum flux and surface velocity are important. As the surface velocity is increased, peak heat transfer rate at the surface reduces, and its position moves downstream with respect to the spray centerline.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Schematic of test apparatus

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Figure 2

Detail of test segment

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Figure 3

Temperature-time histories using 1.70mm nozzle at 2.07MPa, (a) initial temperature 200°C, 60rpm, x=140mm, (b) 500°C, 120rpm, x=240mm

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Figure 4

Surface temperature-time histories at four different mass fluxes, G(kgm−2S−1), at (a) 200°C with rotating disk at 60rpm, and (b) at 500°C at 120rpm

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Figure 5

Schematic diagram for heat flux calculation

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Figure 6

Surface heat flux at temperatures of 200 and 600°C for different conditions

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Figure 7

Effect of spray characteristics on maximum heat flux at temperature 200°C (G, U, and Dv,0.5 were not varied independently of each other)

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Figure 8

Comparison of the measured maximum local heat flux with the heat flux from the correlation equations 1,2,3




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