Study On Coefficient Of Heat Transfer Of Medium Plate Billet High Pressure Water Descaling

The medium plate billet surface was strongly cooled when a large amount of high pressure water clearing oxide scale. The temperature of billet was drop in the same time. In high pressure water descaling process, the heat transfer coefficient between the high pressure water and billet was the important parameters of temperature field analysis. Only computing reasonable convective heat transfer coefficient of high pressure water descaling, it was possible that establishing precisely temperature model before rolling. So it was necessary to analyse and study convective heat transfer coefficient of high pressure water descaling.In this paper, medium plate billet before rolling was the study object in a civil factory. According to the theory of computational fluid dynamics, the velocity field and temperature field of high pressure water descaling were calculated under different conditions. The relation curves between convective heat transfer coefficients of high pressure water descaling and billet surface temperature, the distance between high pressure water jet nozzle and the billet surface, jet nozzle export speed, flow density of high pressure water injecting onto steel plate surface were got.In order to checking if the convective heat transfer coefficients computed by computational fluid dynamics method were reliable or not, on the basis of steel plate interior temperature drop curve of high pressure water descaling that acquired by experiment, the heat transfer coefficients of high pressure water descaling were calculated under experiment conditions by inverse heat transfer method. The results of high pressure water descaling flow field and temperature field were obtained by computational fluid dynamics method under the experiment conditions, and the convective heat transfer coefficients were got. Through comparing the convective heat transfer coefficients that computed by computational fluid dynamics method and inverse heat transfer, the error of convective heat transfer coefficients which were obtained by two computational methods were in reasonable scope. It was proved that the method of computation convective heat transfer coefficient by computational fluid dynamics method was reasonable.The high pressure water convective transfer heat coefficients which were computed under various conditions by computational fluid dynamics method were handled, and the relationships between high pressure water convective transfer heat coefficients and jet distance, the exit velocity of high pressure water and the surface temperature of steel plate were got. Then the mathematical model of high pressure water descaling convective transfer heat coefficient was built on the special condition of a civil medium plate plant by subsection regression method. Last, the undetermined modulus of mathematical model of high pressure water descaling convective transfer heat coefficient were regressed by nonlinear regression method.For setting convective heat transfer coefficient model of high pressure water which was applied to extensive scope, the relationship between heat transfer coefficients and flow density which injecting onto the steel plate surface by high pressure water was studied. And convective heat transfer coefficient model of high pressure water was set, which was used under all conditions. Last, the undetermined modulus of mathematical model of high pressure water descaling convective transfer heat coefficient were regressed by subsection regression method.The high pressure water convective transfer heat coefficient was computed by the mathematical model under corresponding condition in a civil medium plate mill. Based on the coefficient, the billet temperature field before rolling was computed by finite element method. And the billet temperature field before rough rolling was got.For verifying the temperature field obtained by simulation computation was right or not, surface temperatures of billet before rough rolling were measured in medium plate mill. Through comparing measured temperatures and simulation temperatures, it was proved that two results were similar and the regressive mathematical model of high pressure water descaling convective transfer heat coefficient was reasonable. The heat transfer coefficient model was used in temperature model of this factory before rolling. The thickness precision of finish product plate was improved, and the better effect was obtained.