Coupled Calculation Of Flow Field And Temperature Field During Dynamic Quenching Process

Fluid-solid coupled calculation of quenching process has great significance in both theoretical research and engineering application. Research on the interrelationship among the configuration of quenching equipment, the flow filed of quenchant and the temperature field of workpiece is helpful to investigate the factors influencing ultimate quenching effect as well as to guide the design of quenching equipment and quenching process.By means of a computational fluid dynamics software system CFD2000, a simplified fluid-solid coupled heat transfer model was developed in this paper. First, the experimental heat transfer coefficient curves were expressed by a set of mathematical formulae through curve fitting method so as to generate the relationship among the surface temperature of workpiece T, the velocity of quenchant v and the overall heat transfer coefficient h. And then, unique velocity reference point in the quenchant was specified corresponding to each surface grid point. Finally, according to the temperature of surface grid point T and the velocity of corresponding reference point v, linear interpolation among above-mentioned heat transfer coefficient formulae was carried out to get specific heat transfer coefficient h and, thus, the heat transfer boundary conditions were established for coupled calculation, avoiding the complicated calculation of gas-liquid dual-phase flow. In addition, the influence of flow field on the temperature field was analyzed, and experiments were carried out to verify the feasibility of the present numerical method.Through simulation of flow field and temperature field during quenching process in quenching sets with different configurations, it can be found that the difference in the configuration leads to a distinction in the flow field, and ultimately influences the cooling characteristics. On the other hand, the configuration of quenching set can be evaluated and guided based on simulation so as to get uniform flow and cooling effect. As regards those quenching sets with a lot of small holes in the surfaces of inner part, the velocity magnitude increases with the decrease of the inner size, the flow field becomes more complex and non-uniform, and hence the workpiece is cooled down more non-uniformly.In order to verify the feasibility of this simplified coupled method, numerical simulation and experiments of quenching process in a test device for measuring cooling characteristics were carried out at different inlet flow rates, and then comparison and analysis between simulation and experiments were made in the present paper. Results indicate that the simulation fit the experiments well, and the vapor film stage, boiling stage as well as convection stage on simulated cooling rate curves correspond with those on the measured curves. Besides, the temperature regions of vapor film stage and convection stage as well as the cooling rates in these two regions also fit the experiments. For boiling stage, the temperature region agrees with the experiment although the maximum cooling rate offsets the measured result. Therefore, the coupled calculation method can reflect the characteristics of every cooling stage during quenching and it has certain potential for application in simulation of complex quenching process with phase transformation of quenchant itself.