Research Of High Strength And Homogeneous Cooling Heat Transfer Mechanism Of Jet Impingement For Hot Rolled Strip

The ultra fast cooling technology has been widely accepted by the iron and steel production enterprises,which can prompt the product performance by fine grain,precipitation and phase transformation strengthening.The jet impingement heat transfer method was adopted to achieve extraordinary cooling capacity.However,there are many problems to be solved to improve the heat transfer efficiency,achieve homogenous cooling under large heat transfer coefficient,and precisely adjust the cooling technical parameters during industrial application process.This paper relies on National Natural Science Foundation of China(51404058)"The research of high strength and homogeneous cooling heat transfer mechanism and mathematic model for hot rolled strip under the inclined jet impingement",the fundamental heat transfer theory and industrial application based on the UFC process were studied.The main work and achievements are as follows:(1)The laboratory experiment platform was built based on the industry ultra-fast cooling device.The fundamental heat transfer and boiling mechanism and the distribution of wetting region under jet impingement were tested and analyzed.(2)The effect of primary industrial parameters on the heat transfer characteristics and rewetting phenomenon during water jet impingement on a hot plate surface,like initial surface temperature,jet velocity and water temperature,were systematically investigated combined with boiling curves and digital graphs.The cooling curves indicated the initial plate temperature had a significant effect on both the impact and parallel regions,but the water temperature and jet velocity merely showed the remarkable effect in the parallel region.The rewetting temperature depended highly on the initial plate temperature,depended slightly on the water temperature and was almost unaffected by the jet velocity.The wetting velocity initially increased and then declined with the increasing radial distance.The rewetting front propagation was significantly affected by the growth and detachment of the bubbles in the rewetting front region.Equations were regressed to estimate MHF both at stagnation point and in the parallel region,the information provided in this work would be beneficial for predicting the industrial applications of ultra-fast cooling technology.(3)The experiments were carried out to research the heat transfer behavior of double adjacent jets and among triple jets.The vortex appeared due to the interference between adjacent jets under multi-jet impingement,which increased heat transfer coefficient and rewetting velocity.Moreover,the increase ratio became more obvious with the nozzle spacing increasing.The less nozzle spacing corresponded to better uniformity of heat transfer capacity and wetting delay under staggered triple-jet impingement,for the spanwise and streamwise holes spacing changed simultaneously from 20 to 40mm.The larger inclined angle decreased wetting velocity and had less effect on heat transfer capacity between adj acent jets under triplejet inclined impingement,however,MHF initially increased and then declined with the increasing inclined angle for the forward direction.The maximum corresponded inclined angle of 30°.(4)The moving experiment platform was built to research the fundamental heat transfer characteristic of single and array jet impingement.The results showed as follows,wetting region extend outward with oval shape,moreover,heat transfer capacity and wetting velocity along forward direction were greater than lateral direction.Meanwhile,the larger rolled speed can increase the tendency.Heat transfer capacity decreased with the rolled speed increasing nearby impingement region.For jet impingement on moving plate,the wetting behavior and heat transfer process by array jet impingement were similar with single-jet impingement.Besides,comparing with parallel flow region,the heat transfer capacity and wetting velocity in vortex region were larger.