Research And Application Of Heat Transfer Mechanism Of Advanced Plate Cooling System

Controlled cooling technology is an important part of TMCP technology.It can control the phase transformation and carbide precipitation behavior by changing the cooling conditions,and improve the microstructure and properties of the steel plate.The online cooling system is an important part to realize the control cooling technology.Since the plate cooling process involves boiling the water phase change mechanism and surface flow field interference mechanism.It is difficult to achieve efficient heat transfer,uniform heat transfer,and the precise cooling process.Therefore,the further research of cooling mechanism,mathematical model of heat flux,and automation and control systems are important to precise control the plate online cooling process and meet the product requirements.This paper relies on the national twelfth five year science and technology support project "Development and application of new generation TMCP equipment and technology for hot rolled strip" and the national natural science foundation of china"Mechanism and model of high strength uniform cooling for hot rolled strip under inclined jet,No.51404058".The development of advanced cooling system after rolling steel plate with thermal mechanism of water jet impingement and automatic control system were studied.The main work and achievements are as follows:(1)Heat transfer theory research was carried out.State change process under boiling pool boiling conditions were studied.Based on the analysis of jet impingement wall fluid characteristics,the cooling process of the boiling state change process,the survival period of the bubble boiling were analyzed.Jet impingement cooling process of transient boiling is similar as pool boiling,but in a reversed order of each boiling state.On this basis,the cooling mechanism under steady state and transient conditions were studied.(2)A test platform was developed to study the influence of main factors on jet impingement cooling heat transfer characteristics.Through many experiments,the platform was guaranteed great measurement accuracy.The trend of heat transfer area,rewetting mechanism,heat flux increasing speed,and maximum heat flux were studied.The influence of water flux,water temperature,and inclination angle was systematically studied at the same time.The result are helpful for the optimization of mathematical model and cooling system.(3)The characteristics of the multi-jet impinged on high temperature surface were studied experimentally and numercially.Based on the advanced cooling system,experimental and simulation models were built.Combined with vector velocity distribution,turbulent kinetic energy(k),and other heat transfer fluid characteristics and experimental data,multiple jets cooling characteristics,especially the impact of the position of upwelling regions were studied.The results show that the wetting mechanism of mutilpe jets and single jet was close,the wetted region gradually expanding from the impact point.The wetting velocity and heat flux at the upwelling locations will be greater than the parallel flow position,but far less than the impact point.On this basis,the study under industrial condition focused on the effect of different flow rate and roller speed on heat transfer capability.The surface pressure distribution under industrial condition was studied,and the result is helpful for the further understanding of the average heat heat transfer coefficient and heat transfer efficiency.(4)Heat transfer mechanism for impinging jet and air-atomized jet were studied experimentally.The air-atomized jet have a greater surface contact area and impact energy than impinging jet based on unit volume,comparative experimental study on the heat transfer characteristics of the impinging jet and air-atomized jet were implemented.However,the existing nozzle structure has not yet fully comply with the needs of cooling plate line,the further study and improvement are still needed.The results prove that the cooling capacity of air-atomized jet is similar as impinging jet,and air-atomized jet have better cooling uniformity and heat transfer efficiency.The result in this part is helpful for the development of new energy-saving and resource-saving cooling system.(5)After optimizing the core equipment of advanced cooling system,the simulation model was established,and the structure of the water supply system and the uniformity of the pipe were analyzed.The plate on-line cooling process control system was established and optimized,in order to achieve high precision temperature control and heat transfer coefficient of self-learning.On this basis,the stable and fast communication system,precise tracking system,the data storage query system were established,and the automatic cooling function was realized,so as to realize the plate in a cooling line automation and precise control.The development of cooling control system has been successfully applied in production lines.