| Controlled cooling as an important part of TMCP technology has important effect on improving the microstructure and property of the product.In recent years,the ultra-fast cooling technology was widely investigated in domestic and abroad for its superior heat transfer efficiency,strong cooling ability and good cooling uniformity.The jet impingement cooling heat transfer characteristics research is important for improve UFC technology and even promote the progress of TMCP technology.Support by 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 heat transfer mechanism of hot plate cooling by impingement jet and the effects of process parameters such as nozzle height,flow rate and inclination angle were investigated.The major results are as follows:(1)Firstly,the laboratory experiment platform was built based on the industry ultra-fast cooling device.And the inverse heat conduction analysis model was adopted to calculate the distribution of temperature and heat flux.And furthermore,the jet impingement cooling heat transfer mechanism of single circular vertical nozzle and inclined nozzle was tested and analyzed.(2)The effects of process parameters on vertical jet impingement cooling heat transfer process of top surface were studied.The results show that the jet impingement wetting zone is the isotropic circular.The maximum heat flux and wetting speed decrease with the distance between the measure point and the impact point.With the increase of flow rate,the maximum heat flux becomes larger,the wetted zone expands faster,the heat transfer ability of cooling water is enhanced,and the surface temperature is decrease rapidly.When the flow rate increase from 1.5 L/min to 6 L/min,the peak of heat flux at the stagnation point increase from 3.39 MW/m2 to 3.66 MW/m2,the increment reach to 8%,while the peak of heat flux increase from 1.49 MW/m2 to 3.02 MW/m2,of the increment reach to 103%at the location 9;With the increase of nozzle height,the peak of heat flux becomes smaller,the wetted zone expands relatively slowly,the heat transfer ability of cooling water is decreased,and the surface temperature of the hot plate dropped slowly.(3)The effects of process parameters on the vertical jet impingement cooling heat transfer process of bottom surface were studied.The difference between top and bottom surface jet impingement heat transfer was analyzed.The results are useful to adjust the cooling process parameters such as water flow ratio on industry site and to improve the cooling uniformity.The results show that the effects of nozzle height,flow rate on the heat transfer process of bottom surface were the similar as the top surface.But there were also some differences between them.Under the same conditions,The heat flux for top surface jet impingement is larger,however,the rewetting time and the time reached to the heat flux peak for top surface jet impingement is relatively longer;When the flow rate is 1.5 L/min,the nozzle height is 200 mm,the heat flux peak for top surface jet impingement at the stagnation point was 1.1 times than the bottom one.(4)The effect of inclination angle on jet impingement cooling heat transfer process of top surface was studied.The results show that the jet impingement wetted zone is approximately elliptical and anisotropic.At the forward flow direction of jet impingement,the heat flux was the maximum,the wetting time was the shortest,and the lateral flow direction was relatively,the reverse flow direction was the minimum.With the inclination angle increasing,at the forward flow direction of jet impingement,the heat flux becomes larger,the wetting zone expands faster,the heat transfer ability of cooling water is enhanced,but the heat transfer ability of cooling water is decreased at the lateral and reverse flow direction. |
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