The interfacial heat-transfer coefficient at casting/mould interface is a key factor that impacts the simulation accuracy of solidification progress.At present,the simulation result of using available data is comparat...The interfacial heat-transfer coefficient at casting/mould interface is a key factor that impacts the simulation accuracy of solidification progress.At present,the simulation result of using available data is comparatively different from the practice.In the current study,the methods of radial heating and electricity measurement under steady-state condition were employed to study the nature of interfacial heat-transfer between A356 Aluminum alloy and metal mould.The experimental results show that the interfacial heat-transfer between A356 Aluminum alloy and the outer mould drops linearly with time while that of A356 aluminum alloy and the inner mould increases with time during cooling.The interfacial heat-transfer coefficient between A356 aluminum alloy and mould is inversely proportional to the electrical resistance.展开更多
Heat-transfer coefficients(HTC)on surfaces exposed to convection environments are often measured by transient techniques such as thermochromic liquid crystal(TLC)or infrared thermography.In these techniques,the surfac...Heat-transfer coefficients(HTC)on surfaces exposed to convection environments are often measured by transient techniques such as thermochromic liquid crystal(TLC)or infrared thermography.In these techniques,the surface temperature is measured as a function of time,and that measurement is used with the exact solution for unsteady,zero-dimensional(0-D)or one-dimensional(1-D)heat conduction into a solid to calculate the local HTC.When using the 0-D or 1-D exact solutions,the transient techniques assume the HTC and the free-stream or bulk temperature characterizing the convection environment to be constants in addition to assuming the conduction into the solid to be 0-D or 1-D.In this study,computational fluid dynamics(CFD)conjugate analyses were performed to examine the errors that might be invoked by these assumptions for a problem,where the free-stream/bulk temperature and the heat-transfer coefficient vary appreciably along the surface and where conduction into the solid may not be 0-D or 1-D.The problem selected to assess these errors is flow and heat transfer in a channel lined with a staggered array of pin fins.This conjugate study uses three-dimensional(3-D)unsteady Reynolds-averaged Navier-Stokes(RANS)closed by the shear-stress transport(SST)turbulence model for the gas phase(wall functions not used)and the Fourier law for the solid phase.The errors in the transient techniques are assessed by comparing the HTC predicted by the time-accurate conjugate CFD with those predicted by the 0-D and 1-D exact solutions,where the surface temperatures needed by the exact solutions are taken from the time-accurate conjugate CFD solution.Results obtained show that the use of the 1-D exact solution for the semi-infinite wall to give reasonably accurate“transient”HTC(less than 5%〇relative error).Transient techniques that use the 0-D exact solution for the pin fins were found to produce large errors(up to 160%relative error)because the HTC varies appreciably about each pin fin.This study also showed that HTC measured by transient techniques could differ considerably from the HTC obtained under steady-state conditions with isothermal walls.展开更多
In order to improve the control precision of strip coiling temperature for hot strip mill,the BP neural network was combined with mathematical model to calculate convective heat-transfer coefficient of laminar flow co...In order to improve the control precision of strip coiling temperature for hot strip mill,the BP neural network was combined with mathematical model to calculate convective heat-transfer coefficient of laminar flow cooling.The off-line calculated results indicate that the standard deviation of coiling temperature prediction is reduced by 22.84 % with the convective heat-transfer coefficient calculated by BP neural network.The prospects of this method for online application are bright.This method is more helpful to increasing the control precision of coiling temperature for hot strip steel.展开更多
文摘The interfacial heat-transfer coefficient at casting/mould interface is a key factor that impacts the simulation accuracy of solidification progress.At present,the simulation result of using available data is comparatively different from the practice.In the current study,the methods of radial heating and electricity measurement under steady-state condition were employed to study the nature of interfacial heat-transfer between A356 Aluminum alloy and metal mould.The experimental results show that the interfacial heat-transfer between A356 Aluminum alloy and the outer mould drops linearly with time while that of A356 aluminum alloy and the inner mould increases with time during cooling.The interfacial heat-transfer coefficient between A356 aluminum alloy and mould is inversely proportional to the electrical resistance.
基金This research was supported by the National Energy Technology Laboratory of the US Department of Energy with Robin Ames and Richard Dennis as the technical monitors.The authors are grateful for this support.
文摘Heat-transfer coefficients(HTC)on surfaces exposed to convection environments are often measured by transient techniques such as thermochromic liquid crystal(TLC)or infrared thermography.In these techniques,the surface temperature is measured as a function of time,and that measurement is used with the exact solution for unsteady,zero-dimensional(0-D)or one-dimensional(1-D)heat conduction into a solid to calculate the local HTC.When using the 0-D or 1-D exact solutions,the transient techniques assume the HTC and the free-stream or bulk temperature characterizing the convection environment to be constants in addition to assuming the conduction into the solid to be 0-D or 1-D.In this study,computational fluid dynamics(CFD)conjugate analyses were performed to examine the errors that might be invoked by these assumptions for a problem,where the free-stream/bulk temperature and the heat-transfer coefficient vary appreciably along the surface and where conduction into the solid may not be 0-D or 1-D.The problem selected to assess these errors is flow and heat transfer in a channel lined with a staggered array of pin fins.This conjugate study uses three-dimensional(3-D)unsteady Reynolds-averaged Navier-Stokes(RANS)closed by the shear-stress transport(SST)turbulence model for the gas phase(wall functions not used)and the Fourier law for the solid phase.The errors in the transient techniques are assessed by comparing the HTC predicted by the time-accurate conjugate CFD with those predicted by the 0-D and 1-D exact solutions,where the surface temperatures needed by the exact solutions are taken from the time-accurate conjugate CFD solution.Results obtained show that the use of the 1-D exact solution for the semi-infinite wall to give reasonably accurate“transient”HTC(less than 5%〇relative error).Transient techniques that use the 0-D exact solution for the pin fins were found to produce large errors(up to 160%relative error)because the HTC varies appreciably about each pin fin.This study also showed that HTC measured by transient techniques could differ considerably from the HTC obtained under steady-state conditions with isothermal walls.
基金Supported by the National Natural Science Foundation of China (50371069)the Doctoral Foundation of Educational Ministry of China (20030699013)the Basic Aviation Science Foundation of China (04G53044)
基金Item Sponsored by National Natural Science Foundation of China(50104004)
文摘In order to improve the control precision of strip coiling temperature for hot strip mill,the BP neural network was combined with mathematical model to calculate convective heat-transfer coefficient of laminar flow cooling.The off-line calculated results indicate that the standard deviation of coiling temperature prediction is reduced by 22.84 % with the convective heat-transfer coefficient calculated by BP neural network.The prospects of this method for online application are bright.This method is more helpful to increasing the control precision of coiling temperature for hot strip steel.
