High Pressure Spray Cooling of a Moving Surface

Abstract

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 1.35ms−1. 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 0.98to12.5kgm−2s−1 for mass flux, 49-230μm for volume median drop diameter, and 9.8-32.3ms−1 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.