Experimental Study On The Characteristics And Heat Transfer Of Air-mist Jet During Secondary Cooling Of Continuous Casting

Iron and steel material is an important basic material.With the development of iron and steel industry,continuous casting is the core of iron and steel technology.Years of practice has proved that high efficiency continuous casting have become the core link to promote large-scale,high-speed,continuous and compact process.Meanwhile,The application of continuous casting technology greatly reduce consumption,emissions and optimize the quality of steel products.In the whole process of continuous casting,the air-mist jet cooling is one of the key links during the secondary cooling zone,while controlling the heat transfer is the key factor to ensure the quality of continuous casting billets during the secondary cooling in continuous casting zone.The heat transfer in the secondary cooling zone of continuous casting requires that the internal heat of the slab be derived as soon as possible,and the casting speed should be increased as far as possible under limited conditions,meanwhile ensuring the quality of the slab.The heat transfer is the core work of secondary cooling of continuous casting.Based on the air-mist jet cooling during secondary cooling of continuous casting,three efficient experimental platforms were established for different characteristics.The main parameters(velocity and droplet size)of air-mist jet characteristics were analyzed by PIV,LDV,high-speed camera and other modern flow display devices.The air-mist jet under typical operating condition was defined for the air-mist fan-shaped nozzle.Based on the mathematical model of inverse heat transfer problem,the variation law of heat flow on the surface of slab was studied,and the local boiling curve of heat transfer process was established.The heat transfer mechanism of high efficiency continuous casting was explored by the slab heat transfer,cylinder periodic heat transfer with single nozzle air-mist jet cooling and cast billet heat transfer with multi-nozzle array air-mist jet cooling.Above all,the main contents of the research are as follows:(1)To understand the cooling law and heat transfer of secondary cooling,three experimental setups were designed and built independently for heat transfer of air-mist jet in high efficiency continuous casting.The setups can be used to study the characteristics of air-mist jet,the heat transfer of high temperature plate surface and periodic process simulation.In addition,multi-nozzle array of air-mist jet was developed to study the heat transfer characteristics under the boiling state of multi-nozzle.It provides an effective platform and reliable guarantee for the following research and data acquisition.(2)Based on the optical image method,the droplet size of air-mist jet was successfully identified and the accuracy of the method is verified.PIV and LDV were used to measure the droplet velocity of air-mist jet,which revealed the droplet characteristics of air-mist jet,and obtained the criterion equation about spray.It is found that the velocity flow field of air-mist jet has self-similarity and the size distribution of the droplets is even under the a certain working conditions.The typical operating condition of the air-mist nozzle was determined by the results of droplet size,velocity and flow density.The results on the characteristics of air-mist jet can provide the theoretical support for the design and use air-mist jet nozzle during secondary cooling of continuous casting.Meanwhile,it provides an effective method to identify the droplet size of air-mist droplets.(3)The boiling heat transfer characteristic curve of high temperature surface was established.The heat transfer law is found at the temperature range of secondary cooling zone of continuous casting.The heat transfer law was revealed by under different local jet characteristics(droplet velocity and size)using heat transfer on stationary slab,and the heat transfer characteristic equation was fitted;The periodic heat transfer experiment was formed by rotating cylinder which was carried out to reproduce the periodic heat transfer characteristics of air-mist jet cooling,forced convection and air radiation cooling cycles during continuous casting secondary cooling.Periodic heat transfer process caused by periodic heat return inside the cylinder.The influence of periodic boundary conditions is concentrated in the surface region.An experimental correlation is obtained,which can be applied to the practical operation of secondary cooling control by the multi-nozzle array heat transfer experiment.