The accurate material physical properties, initial and boundary conditions are indispensable to the numerical simulation in the casting process, and they are related to the simulation accuracy directly. The inverse he...The accurate material physical properties, initial and boundary conditions are indispensable to the numerical simulation in the casting process, and they are related to the simulation accuracy directly. The inverse heat conduction method can be used to identify the mentioned above parameters based on the temperature measurement data. This paper presented a new inverse method according to Tikhonov regularization theory. A regularization functional was established and the regularization parameter was deduced, the Newton-Raphson iteration method was used to solve the equations. One detailed case was solved to identify the thermal conductivity and specific heat of sand mold and interfacial heat transfer coefficient (IHTC) at the meantime. This indicates that the regularization method is very efficient in decreasing the sensitivity to the temperature measurement data, overcoming the ill-posedness of the inverse heat conduction problem (IHCP) and improving the stability and accuracy of the results. As a general inverse method, it can be used to identify not only the material physical properties but also the initial and boundary conditions' parameters.展开更多
In this paper,the research progress of the interfacial heat transfer in high pressure die casting(HPDC)is reviewed.Results including determination of the interfacial heat transfer coefficient(IHTC),influence of castin...In this paper,the research progress of the interfacial heat transfer in high pressure die casting(HPDC)is reviewed.Results including determination of the interfacial heat transfer coefficient(IHTC),influence of casting thickness,process parameters and casting alloys on the IHTC are summarized and discussed.A thermal boundary condition model was developed based on the two correlations:(a)IHTC and casting solid fraction and(b)IHTC peak value and initial die surface temperature.The boundary model was then applied during the determination of the temperature field in HPDC and excellent agreement was found.展开更多
As an advanced near-net shape technology, squeeze casting is an excellent method for producing high integrity castings. Numerical simulation is a very effective method to optimize squeeze casting process, and the inte...As an advanced near-net shape technology, squeeze casting is an excellent method for producing high integrity castings. Numerical simulation is a very effective method to optimize squeeze casting process, and the interfacial heat transfer coefficient(IHTC) is an important boundary condition in numerical simulation. Therefore, the study of the IHTC is of great significance. In the present study, experiments were conducted and a "plate shape" aluminum alloy casting was cast in H13 steel die. In order to obtain accurate temperature readings inside the die, a special temperature sensor units(TSU) was designed. Six 1 mm wide and 1 mm deep grooves were machined in the sensor unit for the placement of the thermocouples whose tips were welded to the end wall. Each groove was machined to terminate at a particular distance(1, 3, and 6 mm) from the front end of the sensor unit. Based on the temperature measurements inside the die, the interfacial heat transfer coefficient(IHTC) at the metal-die interface was determined by applying an inverse approach. The acquired data were processed by a low pass filtering method based on Fast Fourier Transform(FFT). The feature of the IHTC at the metal-die interface was discussed.展开更多
The high pressure die casting (HPDC) process is one of the fastest growing and most efficient methods for the production of complex shape castings of magnesium and aluminum alloys in today's manufacturing industry...The high pressure die casting (HPDC) process is one of the fastest growing and most efficient methods for the production of complex shape castings of magnesium and aluminum alloys in today's manufacturing industry. In this study, a high pressure die casting experiment using AZ91D magnesium alloy was conducted, and the temperature profiles inside the die were measured. By using a computer program based on solving the inverse heat problem, the metal/die interfacial heat transfer coefficient (IHTC) was calculated and studied. The results show that the IHTC between the metal and die increases right after the liquid metal is brought into the cavity by the plunger, and decreases as the solidification process of the liquid metal proceeds until the liquid metal is completely solidified, when the IHTC tends to be stable. The interfacial heat transfer coefficient shows different characteristics under different casting wall thicknesses and varies with the change of solidification behavior.展开更多
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
The interfacial heat transfer coefficient(IHTC)between the casting and the mould is essential to the numerical simulation as one of boundary conditions.A new inverse method was presented according to the Tikhonov regu...The interfacial heat transfer coefficient(IHTC)between the casting and the mould is essential to the numerical simulation as one of boundary conditions.A new inverse method was presented according to the Tikhonov regularization theory.A regularized functional was established and the regularization parameter was deduced.The functional was solved to determine the interfacial heat transfer coefficient by using the sensitivity coefficient and Newton-Raphson iteration method.The temperature measurement experiment was done to ZL102 sand mold casting,and the appropriate mathematical model of the IHTC was established.Moreover, the regularization method was used to determinate the IHTC.The results indicate that the regularization method is very efficient in overcoming the ill-posedness of the inverse heat conduction problem(IHCP),and ensuring the accuracy and stability of the solutions.展开更多
The interfacial heat transfer coefficient(IHTC)is one of the main input parameters required by casting simulation software.It plays an important role in the accurate modeling of the solidification process.However,its ...The interfacial heat transfer coefficient(IHTC)is one of the main input parameters required by casting simulation software.It plays an important role in the accurate modeling of the solidification process.However,its value is not easily identifiable by means of experimental methods requiring temperature measurements during the solidification process itself.For these reasons,an optimal experiment design was performed in this study to determine the optimal position for the temperature measurement and the optimal thickness of the rectangular cast iron part.This parameter was identified using an inverse technique.In particular,two different algorithms were used:Levenberg Marquard(LM)and Monte Carlo(MC).A numerical model of the solidification process was associated with the optimization algorithm.The temperature was measured at different positions from the mould/metal interface at d=0 mm(mould/metal interface),30 mm,60 mm and 90 mm.the thicknesses of the cast part were:L1=40 mm,60 mm and 80 mm.A comparative study on the IHTC identification was then carried out by varying the initial value of the IHTC between 500 Wm^(-2)K^(-1) and 1050 Wm^(-2)K^(-1).Results showed that the MC algorithm used for estimating the IHTC gives the best results,and the optimal position was at d=30 mm,the position closest to the mould/metal interface,for the lowest thickness L1=40 mm.展开更多
The hydrodynamics and mass transfer characteristics of a lab-scale jet bubbling reactor(JBR)including the gas holdup,volumetric mass transfer coefficient and specific interfacial area were assessed experimentally inve...The hydrodynamics and mass transfer characteristics of a lab-scale jet bubbling reactor(JBR)including the gas holdup,volumetric mass transfer coefficient and specific interfacial area were assessed experimentally investigating the influence of temperature,pH and superficial gas velocity.The reactor diameter and height were 11 and 30 cm,respectively.It was equipped with a single sparger,operating at atmospheric pressure,20 and 40℃,and two pH values of 3 and 6.The height of the liquid was 23 cm,while the superficial gas velocity changed within 0.010-0.040 m·s^(-1)range.Experiments were conducted with pure oxygen as the gas phase and saturated lime solution as the liquid phase.The liquid-side volumetric mass transfer coefficient was determined under unsteady-state oxygen absorption in a saturated lime solution.The gas holdup was calculated based on the liquid height change,while the specific interfacial area was obtained by a physical method based on the bubble size distribution(BSD)in different superficial gas velocities.The results indicated that at the same temperature but different pH,the gas holdup variation was negligible,while the liquid-side volumetric mass transfer coefficient at the pH value of 6 was higher than that at the pH=3.At a constant pH but different temperatures,the gas holdup and the liquid-side volumetric mass transfer coefficients at 40℃were higher than that of the same at 20℃.A reasonable and appropriate estimation of the liquid-side volumetric mass transfer coefficient(kla)in a pilot-scale JBR was provided which can be applied to the design and scale-up of JBRs.展开更多
Mass transfer characteristics have been investigated in a 113 mm diameter asymmetric rotating disk contactor of the pilot plant scale for two different liquid–liquid systems. The effects of operating parameters inclu...Mass transfer characteristics have been investigated in a 113 mm diameter asymmetric rotating disk contactor of the pilot plant scale for two different liquid–liquid systems. The effects of operating parameters including rotor speed and continuous and dispersed phase velocities on the volumetric overall mass transfer coefficients are investigated. The results show that the mass transfer performance is strongly dependent on agitation rate and interfacial tension, but only slightly dependent on phase flow rates. In this study, effective diffusivity is used instead of molecular diffusivity in the Grober equation for estimation of dispersed phase overall mass transfer coefficient.The enhancement factor is determined experimentally and there from an empirical expression is derived for prediction of the enhancement factor as a function of Reynolds number. The predicted results compared to the experimental data show that the proposed correlation can efficiently predict the overall mass transfer coefficients in asymmetric rotating disk contactors.展开更多
As one of the key boundary conditions during casting solidification process, the interfacial heat transfer coefficient (IHTC) affects the temperature variation and distribution. Based on the improved nonlinear estimat...As one of the key boundary conditions during casting solidification process, the interfacial heat transfer coefficient (IHTC) affects the temperature variation and distribution. Based on the improved nonlinear estimation method (NEM), thermal measurements near both bottom and lateral metal-mold interfaces throughout A356 gravity casting process were carried out and applied to solving the inverse heat conduction problem (IHCP). Finite element method (FEM) is employed for modeling transient thermal fields implementing a developed NEM interface program to quantify transient IHTCs. It is found that IHTCs at the lateral interface become stable after the volumetric shrinkage of casting while those of the bottom interface reach the steady period once a surface layer has solidified. The stable value of bottom IHTCs is 750 W/(m^2·℃), which is approximately 3 times that at the lateral interface. Further analysis of the interplay between spatial IHTCs and observed surface morphology reveals that spatial heat transfer across casting-mold interfaces is the direct result of different interface evolution during solidification process.展开更多
Based on Kohler’s ternary solution model and Miedema’s model for calculating the formation heat of binary solution, the integral equation was established for calculating the activity coefficients in ternary alloys a...Based on Kohler’s ternary solution model and Miedema’s model for calculating the formation heat of binary solution, the integral equation was established for calculating the activity coefficients in ternary alloys and intermetallics. The activity coefficients for components in alloy Ti-5Al-2.5Sn, Ti-6Al-4V and intermetallics TiAl, Ti3Al and Ti2AlNb were calculated with the equations. The calculated data coincide well with the experimental ones found in literatures. According to the calculated activity coefficients and activities, it can be predicted that the interfacial reaction in SiC/Ti3Al composite is more severe than that in composites SiC/Ti2AlNb and SiC/TiAl.展开更多
The mass transfer process in a perforated rotating disk contactor(PRDC) using a toluene-acetone-water system was investigated.The volumetric overall mass transfer coefficients are calculated in a PRDC column.Both mass...The mass transfer process in a perforated rotating disk contactor(PRDC) using a toluene-acetone-water system was investigated.The volumetric overall mass transfer coefficients are calculated in a PRDC column.Both mass transfer directions are considered in experiments.The influences of operating variables containing agitation rate,dispersed and continuous phase flow rates and mass transfer in the extraction column are studied.According to obtained results,mass transfer is significantly dependent on agitation rate,while the dispersed and continuous phase flow rates have a minor effect on mass transfer in the extraction column.Furthermore,a novel empirical correlation is developed for prediction of overall continuous phase Sherwood number based on dispersed phase holdup,Reynolds number and mass transfer direction.There has been great agreement between experimental data and predicted values using a proposed correlation for all operating conditions.展开更多
Using the inverse algorithm of heat transfer and the nonlinear estimation method, matching calculated values with measured ones, the interfacial heat transfer coefficient at casting/Cu mould interface was determined.T...Using the inverse algorithm of heat transfer and the nonlinear estimation method, matching calculated values with measured ones, the interfacial heat transfer coefficient at casting/Cu mould interface was determined.The results show that the interfacial heat transfer coefficient at Al/Cu interface changes in a range of 4.0×10 3 1.0×10 5 W·m -2 ·K -1 and its average value is in a range of 5.0×10 37.0×10 3 W·m -2 ·K -1 .展开更多
The interfacial reaction between Ti-6Al-4V alloy and ZrO2 ceramic mold with zirconia sol binder was investigated by keeping the 12 g alloy melt in a vacuum induction furnace for 15 s.The microstructures,element distri...The interfacial reaction between Ti-6Al-4V alloy and ZrO2 ceramic mold with zirconia sol binder was investigated by keeping the 12 g alloy melt in a vacuum induction furnace for 15 s.The microstructures,element distribution and phase constitution of the interface were identified by optical microscopy(OM),scanning electron microscopy(SEM)equipped with energy dispersive spectroscopy(EDS)and X-ray diffraction(XRD).The results show that the whole interface reaction layer can be divided into three regions:metal penetration layer,transition layer,and hardened layer according to the structure morphology,which has the characteristics of severe metal penetration,finer lamellar,and coarse oxygen-richαphase,respectively.The erosion of the alloy melt on the ceramic mold promotes the decomposition of zirconia,which leads to the increase of local Zr concentration,greatly increasing the activity coefficient of Ti,aggravating the occurrence of interfacial reaction.Thus,the interfacial reaction shows the characteristics of chain reaction.When the oxygen released by the dissolution of zirconia exceeds the local solid solubility,it precipitates in the form of bubbles,resulting in blowholes at the interface.The result also indicates that the zirconia mold with zirconia sol binder is not suitable for pouring heavy titanium alloy castings.展开更多
Compared to the resin sand mold casting process, frozen casting is more environmentally friendly, providing a better working environment and enhanced supercooling degree. The interfacial heat transfer coefficient (IHT...Compared to the resin sand mold casting process, frozen casting is more environmentally friendly, providing a better working environment and enhanced supercooling degree. The interfacial heat transfer coefficient (IHTC) between frozen sand mold and metal is an important parameter that significantly influences the final mechanical properties and microstructure of the castings. This paper solved the inverse heat conduction problem using the finite difference method (FDM). In addition, the conjugate gradient method (CGM) was adopted to calculate the temperature distribution and heat flux in the molten metal. At the same time, the particle swarm optimization algorithm (PSO) was used in temperature distribution determination in frozen sand mold. The interfacial heat transfer coefficient (IHTC) was estimated during the solidification of ZL101. The results showed a good agreement between calculated and experimental data, obtaining accurate casting interface temperature Tm, frozen sand mold interface temperature Ts, heat flux q, and IHTC. The analysis of the IHTC variation revealed a water content value within the range of 4 wt.% to 5 wt.% resulted in IHTC in two types of interpretation, called ‘fluctuation type’ and ‘turning type’.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
文摘The accurate material physical properties, initial and boundary conditions are indispensable to the numerical simulation in the casting process, and they are related to the simulation accuracy directly. The inverse heat conduction method can be used to identify the mentioned above parameters based on the temperature measurement data. This paper presented a new inverse method according to Tikhonov regularization theory. A regularization functional was established and the regularization parameter was deduced, the Newton-Raphson iteration method was used to solve the equations. One detailed case was solved to identify the thermal conductivity and specific heat of sand mold and interfacial heat transfer coefficient (IHTC) at the meantime. This indicates that the regularization method is very efficient in decreasing the sensitivity to the temperature measurement data, overcoming the ill-posedness of the inverse heat conduction problem (IHCP) and improving the stability and accuracy of the results. As a general inverse method, it can be used to identify not only the material physical properties but also the initial and boundary conditions' parameters.
基金supported by the National Major Science and Technology Program of China(2012ZX04012011)the National Nature Science Foundation of China(51275269)
文摘In this paper,the research progress of the interfacial heat transfer in high pressure die casting(HPDC)is reviewed.Results including determination of the interfacial heat transfer coefficient(IHTC),influence of casting thickness,process parameters and casting alloys on the IHTC are summarized and discussed.A thermal boundary condition model was developed based on the two correlations:(a)IHTC and casting solid fraction and(b)IHTC peak value and initial die surface temperature.The boundary model was then applied during the determination of the temperature field in HPDC and excellent agreement was found.
基金supported by the National Science and Technology Major Project of China(2017ZX04080001)the National Key Research and Development Program of China(2016YFB0701204)
文摘As an advanced near-net shape technology, squeeze casting is an excellent method for producing high integrity castings. Numerical simulation is a very effective method to optimize squeeze casting process, and the interfacial heat transfer coefficient(IHTC) is an important boundary condition in numerical simulation. Therefore, the study of the IHTC is of great significance. In the present study, experiments were conducted and a "plate shape" aluminum alloy casting was cast in H13 steel die. In order to obtain accurate temperature readings inside the die, a special temperature sensor units(TSU) was designed. Six 1 mm wide and 1 mm deep grooves were machined in the sensor unit for the placement of the thermocouples whose tips were welded to the end wall. Each groove was machined to terminate at a particular distance(1, 3, and 6 mm) from the front end of the sensor unit. Based on the temperature measurements inside the die, the interfacial heat transfer coefficient(IHTC) at the metal-die interface was determined by applying an inverse approach. The acquired data were processed by a low pass filtering method based on Fast Fourier Transform(FFT). The feature of the IHTC at the metal-die interface was discussed.
文摘The high pressure die casting (HPDC) process is one of the fastest growing and most efficient methods for the production of complex shape castings of magnesium and aluminum alloys in today's manufacturing industry. In this study, a high pressure die casting experiment using AZ91D magnesium alloy was conducted, and the temperature profiles inside the die were measured. By using a computer program based on solving the inverse heat problem, the metal/die interfacial heat transfer coefficient (IHTC) was calculated and studied. The results show that the IHTC between the metal and die increases right after the liquid metal is brought into the cavity by the plunger, and decreases as the solidification process of the liquid metal proceeds until the liquid metal is completely solidified, when the IHTC tends to be stable. The interfacial heat transfer coefficient shows different characteristics under different casting wall thicknesses and varies with the change of solidification behavior.
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.
文摘The interfacial heat transfer coefficient(IHTC)between the casting and the mould is essential to the numerical simulation as one of boundary conditions.A new inverse method was presented according to the Tikhonov regularization theory.A regularized functional was established and the regularization parameter was deduced.The functional was solved to determine the interfacial heat transfer coefficient by using the sensitivity coefficient and Newton-Raphson iteration method.The temperature measurement experiment was done to ZL102 sand mold casting,and the appropriate mathematical model of the IHTC was established.Moreover, the regularization method was used to determinate the IHTC.The results indicate that the regularization method is very efficient in overcoming the ill-posedness of the inverse heat conduction problem(IHCP),and ensuring the accuracy and stability of the solutions.
文摘The interfacial heat transfer coefficient(IHTC)is one of the main input parameters required by casting simulation software.It plays an important role in the accurate modeling of the solidification process.However,its value is not easily identifiable by means of experimental methods requiring temperature measurements during the solidification process itself.For these reasons,an optimal experiment design was performed in this study to determine the optimal position for the temperature measurement and the optimal thickness of the rectangular cast iron part.This parameter was identified using an inverse technique.In particular,two different algorithms were used:Levenberg Marquard(LM)and Monte Carlo(MC).A numerical model of the solidification process was associated with the optimization algorithm.The temperature was measured at different positions from the mould/metal interface at d=0 mm(mould/metal interface),30 mm,60 mm and 90 mm.the thicknesses of the cast part were:L1=40 mm,60 mm and 80 mm.A comparative study on the IHTC identification was then carried out by varying the initial value of the IHTC between 500 Wm^(-2)K^(-1) and 1050 Wm^(-2)K^(-1).Results showed that the MC algorithm used for estimating the IHTC gives the best results,and the optimal position was at d=30 mm,the position closest to the mould/metal interface,for the lowest thickness L1=40 mm.
基金the authors appreciate the vice-chancellor of research and technology of the University of Isfahan for supporting this work under Grant No.911401707。
文摘The hydrodynamics and mass transfer characteristics of a lab-scale jet bubbling reactor(JBR)including the gas holdup,volumetric mass transfer coefficient and specific interfacial area were assessed experimentally investigating the influence of temperature,pH and superficial gas velocity.The reactor diameter and height were 11 and 30 cm,respectively.It was equipped with a single sparger,operating at atmospheric pressure,20 and 40℃,and two pH values of 3 and 6.The height of the liquid was 23 cm,while the superficial gas velocity changed within 0.010-0.040 m·s^(-1)range.Experiments were conducted with pure oxygen as the gas phase and saturated lime solution as the liquid phase.The liquid-side volumetric mass transfer coefficient was determined under unsteady-state oxygen absorption in a saturated lime solution.The gas holdup was calculated based on the liquid height change,while the specific interfacial area was obtained by a physical method based on the bubble size distribution(BSD)in different superficial gas velocities.The results indicated that at the same temperature but different pH,the gas holdup variation was negligible,while the liquid-side volumetric mass transfer coefficient at the pH value of 6 was higher than that at the pH=3.At a constant pH but different temperatures,the gas holdup and the liquid-side volumetric mass transfer coefficients at 40℃were higher than that of the same at 20℃.A reasonable and appropriate estimation of the liquid-side volumetric mass transfer coefficient(kla)in a pilot-scale JBR was provided which can be applied to the design and scale-up of JBRs.
文摘Mass transfer characteristics have been investigated in a 113 mm diameter asymmetric rotating disk contactor of the pilot plant scale for two different liquid–liquid systems. The effects of operating parameters including rotor speed and continuous and dispersed phase velocities on the volumetric overall mass transfer coefficients are investigated. The results show that the mass transfer performance is strongly dependent on agitation rate and interfacial tension, but only slightly dependent on phase flow rates. In this study, effective diffusivity is used instead of molecular diffusivity in the Grober equation for estimation of dispersed phase overall mass transfer coefficient.The enhancement factor is determined experimentally and there from an empirical expression is derived for prediction of the enhancement factor as a function of Reynolds number. The predicted results compared to the experimental data show that the proposed correlation can efficiently predict the overall mass transfer coefficients in asymmetric rotating disk contactors.
基金Project(TC160A310-10-01)supported by the National Industry Base Enhanced Program,ChinaProjects(2015B090926002,2013A090100002)supported by Science and Technology of Guangdong Province,ChinaProject(2016AG100932)supported by Key Technology Program of Foshan,China
文摘As one of the key boundary conditions during casting solidification process, the interfacial heat transfer coefficient (IHTC) affects the temperature variation and distribution. Based on the improved nonlinear estimation method (NEM), thermal measurements near both bottom and lateral metal-mold interfaces throughout A356 gravity casting process were carried out and applied to solving the inverse heat conduction problem (IHCP). Finite element method (FEM) is employed for modeling transient thermal fields implementing a developed NEM interface program to quantify transient IHTCs. It is found that IHTCs at the lateral interface become stable after the volumetric shrinkage of casting while those of the bottom interface reach the steady period once a surface layer has solidified. The stable value of bottom IHTCs is 750 W/(m^2·℃), which is approximately 3 times that at the lateral interface. Further analysis of the interplay between spatial IHTCs and observed surface morphology reveals that spatial heat transfer across casting-mold interfaces is the direct result of different interface evolution during solidification process.
文摘Based on Kohler’s ternary solution model and Miedema’s model for calculating the formation heat of binary solution, the integral equation was established for calculating the activity coefficients in ternary alloys and intermetallics. The activity coefficients for components in alloy Ti-5Al-2.5Sn, Ti-6Al-4V and intermetallics TiAl, Ti3Al and Ti2AlNb were calculated with the equations. The calculated data coincide well with the experimental ones found in literatures. According to the calculated activity coefficients and activities, it can be predicted that the interfacial reaction in SiC/Ti3Al composite is more severe than that in composites SiC/Ti2AlNb and SiC/TiAl.
文摘The mass transfer process in a perforated rotating disk contactor(PRDC) using a toluene-acetone-water system was investigated.The volumetric overall mass transfer coefficients are calculated in a PRDC column.Both mass transfer directions are considered in experiments.The influences of operating variables containing agitation rate,dispersed and continuous phase flow rates and mass transfer in the extraction column are studied.According to obtained results,mass transfer is significantly dependent on agitation rate,while the dispersed and continuous phase flow rates have a minor effect on mass transfer in the extraction column.Furthermore,a novel empirical correlation is developed for prediction of overall continuous phase Sherwood number based on dispersed phase holdup,Reynolds number and mass transfer direction.There has been great agreement between experimental data and predicted values using a proposed correlation for all operating conditions.
文摘Using the inverse algorithm of heat transfer and the nonlinear estimation method, matching calculated values with measured ones, the interfacial heat transfer coefficient at casting/Cu mould interface was determined.The results show that the interfacial heat transfer coefficient at Al/Cu interface changes in a range of 4.0×10 3 1.0×10 5 W·m -2 ·K -1 and its average value is in a range of 5.0×10 37.0×10 3 W·m -2 ·K -1 .
基金the National Natural Science Foundation of China(Grant No.51871184)the Natural Science Foundation of Shandong Province(Grant No.ZR2017MEE038)China Postdoctoral Science Foundation(No.2018M642683)。
文摘The interfacial reaction between Ti-6Al-4V alloy and ZrO2 ceramic mold with zirconia sol binder was investigated by keeping the 12 g alloy melt in a vacuum induction furnace for 15 s.The microstructures,element distribution and phase constitution of the interface were identified by optical microscopy(OM),scanning electron microscopy(SEM)equipped with energy dispersive spectroscopy(EDS)and X-ray diffraction(XRD).The results show that the whole interface reaction layer can be divided into three regions:metal penetration layer,transition layer,and hardened layer according to the structure morphology,which has the characteristics of severe metal penetration,finer lamellar,and coarse oxygen-richαphase,respectively.The erosion of the alloy melt on the ceramic mold promotes the decomposition of zirconia,which leads to the increase of local Zr concentration,greatly increasing the activity coefficient of Ti,aggravating the occurrence of interfacial reaction.Thus,the interfacial reaction shows the characteristics of chain reaction.When the oxygen released by the dissolution of zirconia exceeds the local solid solubility,it precipitates in the form of bubbles,resulting in blowholes at the interface.The result also indicates that the zirconia mold with zirconia sol binder is not suitable for pouring heavy titanium alloy castings.
基金supported by the National Key R&D Program of China(No.2021YFB3401200)the Jiangsu Provincial Basic Research Program(Natural Science Foundation)Youth Fund(No.BK20230885).
文摘Compared to the resin sand mold casting process, frozen casting is more environmentally friendly, providing a better working environment and enhanced supercooling degree. The interfacial heat transfer coefficient (IHTC) between frozen sand mold and metal is an important parameter that significantly influences the final mechanical properties and microstructure of the castings. This paper solved the inverse heat conduction problem using the finite difference method (FDM). In addition, the conjugate gradient method (CGM) was adopted to calculate the temperature distribution and heat flux in the molten metal. At the same time, the particle swarm optimization algorithm (PSO) was used in temperature distribution determination in frozen sand mold. The interfacial heat transfer coefficient (IHTC) was estimated during the solidification of ZL101. The results showed a good agreement between calculated and experimental data, obtaining accurate casting interface temperature Tm, frozen sand mold interface temperature Ts, heat flux q, and IHTC. The analysis of the IHTC variation revealed a water content value within the range of 4 wt.% to 5 wt.% resulted in IHTC in two types of interpretation, called ‘fluctuation type’ and ‘turning type’.
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.
