The Effect On Air-mist Jet Of Periodic Heat Transfer

In the continuous casting process,secondary cooling of continuous casting is the most important and controllable.During the whole process,molten steel forms shell in the crystallizer passes through secondary cooling zone,the atomizing nozzle spray atomized water droplets to the hot surface of continuous cast slab with the liquid phase,the surface temperature of the slab rapidly decreases and forms large temperature gradient between the slab surface and the casting center,Heat is rapidly transferred from the center to the surface of the billet,it enables the casting billet to solidify rapidly in a short time and improves the production efficiency.With the improvement of social production and living standards,the required quality of steel is becoming more and more stringent,Hot slab needs to release 60%of the total heat in the stage of continuous casting secondary cooling.The cooling effect of secondary cooling is directly related to the quality of casting billet.The key to control the secondary cooling effect is to control the working parameters of the atomizing nozzle and the drawing speed of the hot casting billet.Therefore,it is particularly important to clearly understand the influence of air-mist jet and the casting billet drawing speed on the casting billet.The characteristics of the air-mist nozzle,the influence law of nozzle air and water pressure on periodic heat transfer were analyzed in detail and the process of heat transfer on the casting slab under different drawing speed.It was simulated by changing the cylinder speed and the characteristics of periodic heat transfer were analyzed.The digital imaging method of droplet size identification was used to measure the change of Sauter mean diameter in the flow field under experimental conditions.The relationship between average particle size and gas-water pressure are analyzedThe results show that the wall surface of the cylinder successively undergoes film boiling,transition boiling,nuclear boiling and forced convection during the spray cooling process of the high-temperature rotating hollow cylinder through the air-mist nozzle.(1)In the film boiling stage and the transition boiling stage,the average heat flux on the wall increases by 32887.5 W/m~2 and 40891 W/m~2 with the press rises,and the heat flux density changes more than the water pressure experiment.(2)In the nuclear boiling stage,the heat flux density of the hollow cylinder wall is more strongly affected by water pressure,and the critical heat flux(Critical Heat Flux-CHF)increases with the increase of water pressure by110208.4W/m~2.The effect of pressure of CHF receives water is more significant;(3)The thermal simulation cylinder speeds are 5r/min,10r/min,15r/min,the experiment found that the overall temperature drop of the cylinder in a single cooling cycle decreases with the increase of the speed,and the overall cooling rate decreases The cooling time is increased by 78s,the heat flux density on the surface of the cylinder is low,and the critical heat flux density CHF value decreases with the increase of the speed 263057.25W/m~2,and the Leidenfrost temperature point is delayed.