Research On Test Of Heat Transfer Coefficients And Optimization Of Water Flows For Secondary Cooling Zones In Continuous Casting

As the central part of steel production,continuous casting plays an important role in ensuring the processing performance and usage performance of steel products.Therein the secondary cooling zone is the key to influence the quality of billets.For improving the quality of billets,optimization of secondary cooling water flows based on solidification model is an effective way,and the heat transfer coefficients(HTC)accuracy of secondary cooling zone is the basis to ensure the reliability of the model.In this thesis,HTC of secondary cooling zones are studied by experimental method,and the relationship between HTC,flow density and the billet surface temperature is obtained based on the experimental data of cold test and hot test of the nozzles.And HTC are finally applied to the modeling of continuous casting billets and the optimization of secondary cooling water flows.The main research contents of this thesis are as follows:(1)Experiment study of cold test and hot test of nozzles for continuous casting billets.In the cold test system,by collecting water with the tubes,the relationship between the distribution of water flow density and nozzle flow rate,pressure is determined.In the hot test system,a new method for measuring temperature is presented.In the method,the influence of uneven distribution of water flow density and the installation location of thermocouple on temperature measurement is considered.By hot test,the non-steady cooling curves under different air pressures and flow rates are obtained,establishing the foundation for solving HTC.(2)Numerical solving of HTC based on improved Tikhonov regularization algorithm.HTC are back-calculated based on heat transfer model with the nozzle experiment data.In order to ensure the stability and accuracy of solution,the Tikhonov regularization algorithm is adopted and improved to solve the HTC.In the algorithm,particle swarm optimization algorithm is used to determine the regularization parameter a.Through numerical experiments,errors of solved HTC by improved Tikhonov regularization algorithm are less than 5%,it has high accuracy of solution.Finally,HTC under different water flow densities and billet surface temperatures are obtained by back calculation algorithm,and corresponding analytical formulas are fitted.(3)Accuracy verification of HTC for different secondary cooling zones.The heat transfer coefficient formulas are applied to the solidification and heat transfer model.With accurate boundary conditions by considering the non-uniform distribution of water flow density in secondary cooling zones,deviation between calculations and measurements of billet surface temperatures are not greater than 6.9℃,while the deviation by empirical formula is 16.7℃.It indicates a high accuracy of the heat transfer coefficients obtained by former test.(4)Study on optimization of secondary cooling water flows for continuous casting billets.The optimization model is established based on the established formulas of HTC,which improves the reliability of the research.Besides,the optimization algorithm is improved.In the chaos particle swarm optimization algorithm,considering the poor effect by simply dealing with the inert particles using chaos sequence,chaos factor r is introduced into the moving process of particles to improve the optimizing solution.Through numerical experiments,the algorithm shows better global search ability.Using the algorithm,the secondary cooling water flows are optimized,and new recipe for secondary cooling are determined and applied in production.