Cooling of a rotating cylinder by a subcooled planar jet - Influence of the surface velocity on boiling regime

摘要

Cooling from impinging jet is nearly compulsory in steel industry processing especially in Run Out Table processing and steel tube production because of the high heat transfer provided by the boiling of the subcooled water jet. As far as metallurgical phase transformations, residual stresses and deformations in the workpiece are concerned, the temperature drop during cooling must be controlled thanks to a full understanding of the heat transfer mechanisms. One of the main characteristic using jet impingement is that the transition boiling regime may exist for very high superheat and thus the Leidenfrost temperature is higher than in pool boiling; consequently, boiling curves generally have a particular shape in the transition boiling regime which is usually called "shoulder of flux". In this study, an innovative experimental quenching device has been used for analyzing the effect of the wall velocity of the surface to be cooled on the boiling curves (i.e. heat transfer) and we especially point out that the "shoulder of flux" (i.e. transition boiling regime) is strongly dependent on the surface to jet velocity ratio (r~*). We found that a very small increase of the wall velocity has a high influence on shoulder of flux collapse.