A thermal multiphase lattice Boltzmann(LB) model is used to study the behavior of droplet impact on hot surface and the relevant heat transfer properties.After validating the correctness of the codes through the D^(2)...A thermal multiphase lattice Boltzmann(LB) model is used to study the behavior of droplet impact on hot surface and the relevant heat transfer properties.After validating the correctness of the codes through the D^(2) law,the simulations of intrinsic contact angle and the temperature-dependent surface tension are performed.The LB model is then used to simulate the droplet impact on smooth and micro-hole heated surface.On the smooth surface,the impinging droplet is reluctant to rebound,unless the intrinsic wettability of the solid surface is fairly good.On the micro-hole surface,however,the micro-holes provide favorable sites for generating a high-pressure vapor cushion underneath the impinging droplet,which thereby facilitates the continuous droplet rebound.For the continuously rebounding droplet.The time evolution of volume and temperature display obvious oscillations.The achievable height of the rebounding droplet increases as the intrinsic wettability of the solid surface becomes better,and the maximum transient heat flux is found to be directly proportional to the droplet rebounding height.Within a certain time interval,the continuous rebounding behavior of the droplet is favorable for enhancing the total heat quantity/heat transfer efficiency,and the influence of intrinsic wettability on the total heat during droplet impingement is greater than that of the superheat.The LB simulations not only present different states of droplets on hot surfaces,but also guide the design of the micro-hole surface with desirable heat transfer properties.展开更多
A three-dimensional numerical model coupling the macrosegregation and magnetohydrodynamic simulations was developed to investigate the effects of electromagnetic stirring(EMS)on the macrosegregation.The results show t...A three-dimensional numerical model coupling the macrosegregation and magnetohydrodynamic simulations was developed to investigate the effects of electromagnetic stirring(EMS)on the macrosegregation.The results show that a significant swirling flow was induced by the in-mold EMS,which further changed the shape of the solidification shell and homogenized the solute elements in mold.However,the effects were only confined to the initial billet shell.The improvement in centerline segregation was observed with the usage of the final EMS(F-EMS),which led to the forced convection at the final solidification stage.The solute elements in the mushy zone were significantly even,with the maximum segregation degree of solute C reducing from 1.311 to 1.237.In addition,the effects of the stirrer positions and currents of F-EMS on the macrosegregation alleviation were numerically studied.Different values of centerline segregation were predicted with various stirrer positions and currents,and there is an optimum stirrer parameter to obtain the best macrosegregation alleviation.In the experimental conditions,the optimum position was about 7 m away from meniscus,and the optimum current was 300 A.展开更多
基金financially supported by the Major Program of the National Natural Science Foundation of China (No. U1864209)the “Qinglan” Project of Jiangsu Province, China。
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51901148 and 51874204)the Fund of the State Key Laboratory of Solidification Processing(Northwestern Polytechnical University),China(Grant No.SKLSP202006)。
文摘A thermal multiphase lattice Boltzmann(LB) model is used to study the behavior of droplet impact on hot surface and the relevant heat transfer properties.After validating the correctness of the codes through the D^(2) law,the simulations of intrinsic contact angle and the temperature-dependent surface tension are performed.The LB model is then used to simulate the droplet impact on smooth and micro-hole heated surface.On the smooth surface,the impinging droplet is reluctant to rebound,unless the intrinsic wettability of the solid surface is fairly good.On the micro-hole surface,however,the micro-holes provide favorable sites for generating a high-pressure vapor cushion underneath the impinging droplet,which thereby facilitates the continuous droplet rebound.For the continuously rebounding droplet.The time evolution of volume and temperature display obvious oscillations.The achievable height of the rebounding droplet increases as the intrinsic wettability of the solid surface becomes better,and the maximum transient heat flux is found to be directly proportional to the droplet rebounding height.Within a certain time interval,the continuous rebounding behavior of the droplet is favorable for enhancing the total heat quantity/heat transfer efficiency,and the influence of intrinsic wettability on the total heat during droplet impingement is greater than that of the superheat.The LB simulations not only present different states of droplets on hot surfaces,but also guide the design of the micro-hole surface with desirable heat transfer properties.
基金the China Postdoctoral Science Foundation(No.2018M642308)Jiangsu Planned Projects for Postdoctoral Research Funds(No.2018K068C).
文摘A three-dimensional numerical model coupling the macrosegregation and magnetohydrodynamic simulations was developed to investigate the effects of electromagnetic stirring(EMS)on the macrosegregation.The results show that a significant swirling flow was induced by the in-mold EMS,which further changed the shape of the solidification shell and homogenized the solute elements in mold.However,the effects were only confined to the initial billet shell.The improvement in centerline segregation was observed with the usage of the final EMS(F-EMS),which led to the forced convection at the final solidification stage.The solute elements in the mushy zone were significantly even,with the maximum segregation degree of solute C reducing from 1.311 to 1.237.In addition,the effects of the stirrer positions and currents of F-EMS on the macrosegregation alleviation were numerically studied.Different values of centerline segregation were predicted with various stirrer positions and currents,and there is an optimum stirrer parameter to obtain the best macrosegregation alleviation.In the experimental conditions,the optimum position was about 7 m away from meniscus,and the optimum current was 300 A.
