Heat Transfer Under An Air-water Cooling Jet

Abstract

The solidification and cooling of a continuously cast billet, slab or cylinder—generally a concasting—and the simultaneous heating of the crystallizer is a very complicated problem of three-dimensional (3D) transient heat and mass transfer. The solving of such a problem is impossible without numerical models of the temperature field of the concasting itself while it is being processed through the concasting machine (CCM). Experimental research and measurements have to take place simultaneously with numerical computation, not only to be confronted with the numerical model but also to make it more accurate throughout the process. An important area of the CCM is the so-called secondary cooling zone, which is subdivided into thirteen sections, where the first section uses water jets from all sides of the concasting and the remaining twelve sections engage air-water cooling jets positioned only on the upper and lower sides of the concasting. A great number of experiments had also been conducted on an experimental laboratory device simulating the surface of a concasting in order to determine the intensity of the cooling jets. A real CCM contains a total of 8 types of jets and geometrical layouts. All of these jets had been measured individually on the actual laboratory device, which allows the measurement of temperatures beneath the surface of the slab, and which also simulates the movement of the slab. The measured temperatures are converted to cooling intensities by means of an inverse task, which, in turn, are converted to the courses of the heat transfer coefficients. These coefficients are used as the main input data of the numerical model of the temperature field. The numerical model serves also to determine the effect of radiation. The course of the reduced heat transfer coefficient will be illustrated. It is obvious that radiance is dependent on the surface temperature. The results of numerical simulation of the temperature field of a