Numerical Analysis for Film Boiling Heat Transfer of a Moving Hot Steel Plate

概要

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The cooling of the steel strip in ROT (run out table) of the hot rolling process is very important in that the ROT is the final process to control the mechanical properties of the final products. In general the products are cooled by the circular water jets which makes the comparatively thick residual water layer about 100–200 mm with the supplied flow rate on the plate. The basic phenomenon governing this cooling process is the boiling heat transfer. The boiling phenomenon is one of the most well-understood heat transfer mechanism by the past a few decades research. However, almost all the results have been reached through experimentation. This paper focuses on the boiling heat transfer on the moving hot plate with a fully numerical approach. The simulation was conducted only in a very high temperature region (over the Leidenfrost temperature) where the film boiling can be kept steadily on the plate. The film (the steam layer) was regarded as the heat resistance whose capacity (actually the steam layer thickness) varied with the plate surface temperature and the flow rate and temperature of the water jet. To fix the steam layer thickness showing a very different spatially distribution on the plate, the continuity for the temperature and heat flux at the interface between the cooling water and the steam layer is satisfied by the iterative procedure for the effective thermal conductivity of the 1st cell on the plate wall.