This paper studied a certain blade with ten radial cooling holes which employed conjugate heat transfer method. The cooling air entered the cooling channel from the bottom of the blade and went out from the top, it wa...This paper studied a certain blade with ten radial cooling holes which employed conjugate heat transfer method. The cooling air entered the cooling channel from the bottom of the blade and went out from the top, it was not ejected into the main flow. This paper used different numerical conditions including different turbulence models,turbulence intensities,thermal conduction coefficients and the influence on fluid property via temperature variation. The temperature distribution and pressure distribution of the blade were compared with experimental data. The results show that the numerical results using different turbulence models are almost identical to experimental data even little deviation occurs at shock wave location. The trends of temperature distribution under different numerical conditions are coincident to experimental data,especially Reynolds stress turbulence model. It can be concluded that anisotropic turbulence models can simulate the transition from laminar to turbulence,and the influence of turbulence intensity on laminar region and transition region is more than that on developed turbulent region.展开更多
In this paper, a 3D model of a flat circuit board with a heat generating electronic chip mounted on it has been studied numerically. The conjugate heat transfer including the conduction in the chip and convection with...In this paper, a 3D model of a flat circuit board with a heat generating electronic chip mounted on it has been studied numerically. The conjugate heat transfer including the conduction in the chip and convection with the surrounding fluid has been investigated numerically. Computational fluid dynamics using the finite volume method has been used for modeling the conjugate heat transfer through the chip and the circuit board. Conjugate heat transfer has broad applications in engineering and industrial applications in design of cooling off electronic components. Effects of various inlet velocities have been studied on the heat transfer variation and temperature of the circuit board. Numerical results show that the temperature of the chip reduces as the velocity of the inlet fluid flow increases.展开更多
In this paper,we present a unified finite volume method preserving discrete maximum principle(DMP)for the conjugate heat transfer problems with general interface conditions.We prove the existence of the numerical solu...In this paper,we present a unified finite volume method preserving discrete maximum principle(DMP)for the conjugate heat transfer problems with general interface conditions.We prove the existence of the numerical solution and the DMP-preserving property.Numerical experiments show that the nonlinear iteration numbers of the scheme in[24]increase rapidly when the interfacial coefficients decrease to zero.In contrast,the nonlinear iteration numbers of the unified scheme do not increase when the interfacial coefficients decrease to zero,which reveals that the unified scheme is more robust than the scheme in[24].The accuracy and DMP-preserving property of the scheme are also veri ed in the numerical experiments.展开更多
The boiling heat transfer technology with cavity surfaces can provide higher heat flux under lower wall superheat,which is of great significance for the cooling of electronic chips and microelectromechanical devices.I...The boiling heat transfer technology with cavity surfaces can provide higher heat flux under lower wall superheat,which is of great significance for the cooling of electronic chips and microelectromechanical devices.In this paper,the boiling characteristics of the cavity surfaces are investigated based on the lattice Boltzmann(LB)method,focusing on the effects of cavity shapes,sizes,and heater thermal conductivity on the heat transfer performance.The results show that the triangular cavity has the best boiling performance since it has less residual vapor and higher bubble departure frequency than those of the trapezoidal and rectangular cavities.As the cavity size increases,the enhancement of heat transfer by the cavity mouth is suppressed by the heat accumulation effect at the heater bottom.The liquid rewetting process during bubble departure is the reason for the fluctuation of the space-averaged heat flux,and the heater thermal conductivity determines the fluctuation amplitude.The evaporation of liquid in the cavity with high thermal conductivity walls is more intense,resulting in shorter waiting time and higher bubble departure frequency.展开更多
Film cooling combined with internal impingement cooling is one of the most effective technologies to protect the gas turbine vanes and blades from the hot gas. In this study, conjugate heat transfer CFD study was unde...Film cooling combined with internal impingement cooling is one of the most effective technologies to protect the gas turbine vanes and blades from the hot gas. In this study, conjugate heat transfer CFD study was undertaken for a flat plate with combined film cooling and impingement cooling. An experiment on conjugate heat transfer of a flat plate with combined film and impingement cooling was performed to validate the code. Then the effects of several parameters including Biot number, blowing ratio, film hole shape and impingement hole diameter on the overall cooling effectiveness were numerically studied. The results show that for a specific combined cooling scheme and a given blowing ratio, the coolant potential can be reasonably allocated to the internal and the external cooling to achieve the overall cooling effectiveness. As the blowing ratio increases, the overall cooling effectiveness trends to reach a maximum value. For different film hole geometrical, the maximum values of the overall cooling effectiveness at high blowing ratio approximate to the same value. At a given mass flow rate of coolant, the increase of the impingement hole diameter leads to the reduction of the overall cooling effectiveness.展开更多
The preconditioned density-based conjugate heat transfer(CHT)algorithm was used to investigate the heat transfer characteristics of a cooled turbine vane.Fluid domain provided boundary heat flux for solid domain and o...The preconditioned density-based conjugate heat transfer(CHT)algorithm was used to investigate the heat transfer characteristics of a cooled turbine vane.Fluid domain provided boundary heat flux for solid domain and obtained boundary temperature from it for the coupling strategy.The governing equations were solved by the preconditioned density-based finite-volume method,with preconditioning matrix,improved Abu-Gharmam Shaw(AGS)transition model,matrix dissipation scheme and four kinds of turbulence models.The grid system is multi-block structured grids for fluid domain and unstructured grids for solid domain,with full-matched grids at the fluid-solid interfaces.The effects of turbulence model,outlet Mach number,outlet Reynolds number,inlet turbulence intensity and the temperature ratio of blade surface/gas on the local heat transfer performance were studied.Results indicate that the k-o shear-stress transport(SST)and AGS model can predict the conjugate heat transfer better than others.The Mach number and Reynolds number have relatively obvious influences on the heat transfer,while the turbulence intensity and temperature ratio only have slight influences.Comparisons with experimental data demonstrate the applicability and accuracy of the numerical algorithm.展开更多
Reliable transient thermal analysis plays a very important role in the engine safety analysis.Transient conjugate heat transfer simulation is an important way of temperature analysis.But there exists a great disparity...Reliable transient thermal analysis plays a very important role in the engine safety analysis.Transient conjugate heat transfer simulation is an important way of temperature analysis.But there exists a great disparity in the time scales between solid conduction and fluid convection.The calculation cost of transient conjugate heat transfer analysis is very huge because of the tiny time step of computational fluid dynamics.The Bi-Fo time scaling method is proposed to improve the computational efficiency of transient conjugate heat transfer.On the one hand,this method carries out a similar transformation on solid heat conduction,scaling the calculation time with the product of density and specific heat capacity to maintain the consistency of Fourier number.On the other hand,it takes very short time for the fluid domain to recover stability after a boundary disturbance.Based on the above characteristic,the flow time is directly compressed to the same as that of the solid domain.It is verified by Mark II vane that increasing the solid thermal diffusivity can reduce the time scale of heat conduction.In the situation of rapidly stable flow field,scaling flow time does not affect the solid thermal boundary under corresponding dimensionless time.Within the application scope,the Bi-Fo time scaling method can greatly reduce the time cost of transient conjugate heat transfer simulation while maintaining the accuracy of transient temperature analysis.展开更多
A unified solution framework is proposed for efficiently solving conjugate fluid and solid heat transfer problems.The unified solution is solely governed by the compressible Navier-Stokes(N-S)equations in both fluid a...A unified solution framework is proposed for efficiently solving conjugate fluid and solid heat transfer problems.The unified solution is solely governed by the compressible Navier-Stokes(N-S)equations in both fluid and solid domains.Such method not only provides the computational capability for solid heat transfer simulations with existing successful N-S flow solvers,but also can relax time-stepping restrictions often imposed by the interface conditions for conjugate fluid and solid heat transfer.This paper serves as Part I of the proposed unified solution framework and addresses the handling of solid heat conduction with the nondimensional N-S equations.Specially,a parallel,adaptive high-order discontinuous Galerkin unified solver has been developed and applied to solve solid heat transfer problems under various boundary conditions.展开更多
By investigating heat transfer and flow structures of dimples,orthogonal ribs,and V-shaped ribs in the impingement/effusion cooling,the article is dedicated to selecting a best-performing internal cooling structure fo...By investigating heat transfer and flow structures of dimples,orthogonal ribs,and V-shaped ribs in the impingement/effusion cooling,the article is dedicated to selecting a best-performing internal cooling structure for a turbine vane.The overall cooling effectiveness and coolant consumption are adopted to evaluate the cooling performance.To analyze the influence of structural modification,the flow field is investigated on chordwise/spanwise sections and the target surface.The blockage effect on crossflow can protect jet flow,resulting in higher heat transfer performance of the target surface.Ribs own a stronger blockage effect than dimples.Compared with the blockage effect,the influence of the rib shape is negligible.By installing dimples between ribs,heat transfer is augmented further.The introduction of ribs/dimples leads to higher discharge coefficients of jet nozzles but lower discharge coefficients of film holes.Thus,the film cooling deteriorates.Meanwhile,the installation of the ribs and dimples decreases total coolant consumption.The effect of ribs/dimples on heat transfer and effusion condition of internal and external cooling is analyzed.The best-performing cooling structure is the target surface with dimples and orthogonal ribs,which decreases the wall temperature and coolant consumption by 14.57-28.03 K and 1.19%-1.81%respectively.This article concludes the flow mechanism for dimples and influence factors on the cooling performance,which may serve as guidance for the turbine vane design.展开更多
The present study proposes a predictive model to explore the effect of partially filled porous media on the con-jugate heat transfer characteristic of phase change material(PCM)with interfacial coupling conditions bet...The present study proposes a predictive model to explore the effect of partially filled porous media on the con-jugate heat transfer characteristic of phase change material(PCM)with interfacial coupling conditions between pure fluid region and porous region.The enthalpy-porosity method,local thermal non-equilibrium model and Darcy-Forchheimer law are comprehensively considered to describe the convective heat transfer process in porous media.The modified model is then validated by benchmark data provided by particle image velocimetry(PIV)ex-periments.The phase change behavior,heat transfer efficiency and energy storage performance are numerically investigated for different partial porous filling strategies in terms of filling content,position,height of porous foam and inclination angles of cavity.The results indicate that due to the resistance in porous region,the shear stress exerted by the main vortex(natural convection)in pure fluid region and the momentum transferred,a secondary vortex phenomenon appears in the porous region near the fluid/porous interface.Moreover,such dis-continuity of permeability and fluid-to-porous thermal conductivity results in the cusp of phase change interface at the horizontal fluid/porous boundary.Among four partial porous filling cases,the lower porous filling one has more desirable heat transfer performance,and the 3/4H lower porous filling configuration is the best solution for optimization of the latent heat thermal energy storage(LHTES)systems.For tilted cavity,the increase of inclination angle positively affects the heat transfer efficiency as well as the energy storage rate of the LHTES system,where the performance of 3/4H lower porous filling configuration is further highlighted.展开更多
To study the seepage and deformation characteristics of coal at high temperatures,coal samples from six different regions were selected and subjected to computed tomography(CT)scanning studies.In conjunction with ANSY...To study the seepage and deformation characteristics of coal at high temperatures,coal samples from six different regions were selected and subjected to computed tomography(CT)scanning studies.In conjunction with ANSYS software,3 D reconstruction of CT images was used for the establishment of fluidsolid conjugate heat transfer model and coal thermal deformation model based on the microstructures of coal.In addition,the structure of coal was studied in 2 D and 3 D perspectives,followed by the analysis of seepage and deformation characteristics of coal at high temperatures.The results of this study indicated that porosity positively correlated with the fractal dimension,and the connectivity and seepage performances were roughly identical from 2 D and 3 D perspectives.As the porosity increased,the fractal dimension of coal samples became larger and the pore-fracture structures became more complex.As a result,the permeability of coal samples decreased.In the meantime,fluid was fully heated,generating high-temperature water at outlet.However,when the porosity was low,the outlet temperature was very high.The average deformation of coal skeleton with different pore-fracture structures at high temperatures showed a trend of initial increase and subsequent decrease with the increase of porosity and fractal dimension.The maximum deformation of coal skeleton positively correlated with connectivity but negatively correlated with the fractal dimension.展开更多
Focusing on the design problem of high-performance radiators for planar motors in the wafer stage of the lithography machine,a thermal-fluid coupling optimization scheme based on parametric solid components was propos...Focusing on the design problem of high-performance radiators for planar motors in the wafer stage of the lithography machine,a thermal-fluid coupling optimization scheme based on parametric solid components was proposed.The mapping method between component parameters and pseudo-density values was established.An analytical solution for the sensitivity of pseudo-density to component parameters was given.The conjugate heat transfer function with the shallow channel approximation term was solved through the pseudo-density information.In the optimization example,circular components were selected,and the position and the size of solid components were chosen as design variables.In order to eliminate calculation errors caused by pseudo-density,an optimized pseudo-density field was converted into the result based on parametric components.Compared to the reference motor radiator,the average surface temperature rise of the optimized water-cooling motor radiator is reduced by 22.4%,which verifies the feasibility and effectiveness of the proposed method.展开更多
This paper implemented cooling configuration design on certain gas turbine HP rotor using parameterized method.It is convenient for complicated gas turbine blade modeling using parameters and also benefit for the geom...This paper implemented cooling configuration design on certain gas turbine HP rotor using parameterized method.It is convenient for complicated gas turbine blade modeling using parameters and also benefit for the geometry modify in later period.Parameterized modeling is the foundation of air cooling turbine blade design method engineering application.Mesh quality can be awarded when generated complicated cooling configuration blade grids,and also the increase of calculation error can arise by many mesh blocks.Film cooling and serpentine passage can effectively enhance the cooling effectiveness and protect blade.展开更多
As turbine inlet temperature gets higher and higher,thermal barrier coating(TBC) is more and more widely used in turbine blades.For turbine blades with TBC,it is of great significance to evaluate the temperature distr...As turbine inlet temperature gets higher and higher,thermal barrier coating(TBC) is more and more widely used in turbine blades.For turbine blades with TBC,it is of great significance to evaluate the temperature distribution of its substrate metal quickly and accurately,especially during the design stage.With different degrees of simplification such as whether to consider the change of the geometric size of the fluid domain by TBC and whether to consider the planar heat conduction in TBC,three different methods used in conjugate heat transfer(CHT) simulation to model the TBC of the turbine blades have been developed and widely used by researchers.However,little research has been conducted to investigate the influence of the three methods on the temperature distribution of turbine blade.To fill this gap,three geometric models were designed.They are a solid conduction model with a substrate metal layer and a TBC layer,a transonic turbine vane with internal cooling and TBC,and a plate cylindrical film hole cooling model with TBC.Different methods were used in these geometric models and their differences were carefully analyzed and discussed.The result shows that for the conduction model used in this paper,with the same TBC surface temperature distribution,the difference between the three methods is very small and can be ignored.For a transonic turbine vane with internal cooling,regarding the local maximum temperature of the substrate-TBC interface,the largest difference between the method in which TBC is considered as a thermal resistance or a virtual layer of cells and the method in which three-dimensional heat conduction equation of TBC is solved occurs at the trailing edge.The difference near the leading edge is below 2K.When employed to the film cooling model,the difference of the laterally averaged temperature of the substrate-TBC interface can be 8 K which is mainly due to the change of the length to diameter ratio of the film cooling hole by TBC.If the substrate thickness is reduced by the thickness of TBC when three-dimensional heat conduction equation of TBC is solved,the temperature difference between the three methods will be quite limited.展开更多
Great efforts are still put into the design process of advanced film-cooling configurations.In particular,the vanes and blades of turbine front stages have to be cooled extensively for a safe operation.The conjugate c...Great efforts are still put into the design process of advanced film-cooling configurations.In particular,the vanes and blades of turbine front stages have to be cooled extensively for a safe operation.The conjugate calculation technique is used for the three dimensional thermal load prediction of a fim-cooled test blade of a modern gas turbine.Thus,it becomes possible to take into account the interaction of internal flows,external flow,and heat transfer without the prescription of heat transfer ooefficients.The focus of the investigation is laid on the leading edge part of the blade.The numerical model consists of all internal flow passages and cooling hole rows at the leading edge.Furthermore,the radial gap flow is also part of the model.The comparison with thermal pyrometer measurements shows that with respect to regions with high thermal load a qualitatively and quantitatively good agreement of the conjugate results and the measurements can be found.In particular,the region in the vicinity of the mid-span section is exposed to a higher thermal load,which requires further improvement of the cooling arrangement.Altogether the achieved results demonstrate that the conjugate calculation technique is applicable for reasonable prediction of three-dimensional thermal load of complex cooling configurations for blades.展开更多
Conjugate heat transfer is numerically investigated using a three-dimensional computational fluid dynamics approach in various microchannel geometries to identify a high-performance cooling method for piezoelectric ce...Conjugate heat transfer is numerically investigated using a three-dimensional computational fluid dynamics approach in various microchannel geometries to identify a high-performance cooling method for piezoelectric ceramic stacks and spindle units in high-precision machines.Straight microchannels with rectangular cross sections are first considered,showing the performance limitations of decreasing the size of the microchannels,so other solutions are needed for high applied heat fluxes.Next,many microchannel designs,focusing on streamwise geometric variation,are compared to straight channels to assess their performances.Sinusoidally varying channels produce the highest heat transfer rates of those studied.Thus,their optimization is considered at a channel width and height of 35 and 100μm,respectively.Heat transfer increases as the amplitude and spatial frequencies of the channels increase due to increased interfacial surface area and enhanced Dean flow.The highest performance efficiencies are observed at intermediate levels of amplitude and frequency,with efficiency decreasing as these geometric parameters are increased further at the onset of flow separation.The sinusoidal channel geometries are then optimized with respect to minimizing the system’s pressure drop for all applied heat fluxes between 5690 and 6510 kW/m2.Doing so created an optimal geometry curve and showed that all geometries in this region had amplitudes close to 40μm.Therefore,imposing a fixed heat flux requirement for a case study of cooling piezoelectric ceramics,the optimized sinusoidal geometry decreases the system pressure drop by 79%relative to a straight channel while maintaining a larger minimum feature size.展开更多
A novel building integrated photovoltaic thermal(BIPVT)roofing panel has been designed considering both solar energy harvesting efficiency and thermal performance.The thermal system reduces the operating temperature o...A novel building integrated photovoltaic thermal(BIPVT)roofing panel has been designed considering both solar energy harvesting efficiency and thermal performance.The thermal system reduces the operating temperature of the cells by means of a hydronic loop integrated into the backside of the panel,thus resulting in maintaining the efficiency of the solar panels at their feasible peak while also harvesting the generated heat for use in the building.The performance of the proposed system has been evaluated using physical experiments by conducting case studies to investigate the energy harvesting efficiency,thermal performance of the panel,and temperature differences of inlet/outlet working liquid with various liquid flow rates.The physical experiments have been simulated by coupling the finite element method(FEM)and finite volume method(FVM)for heat and mass transfer in the operation.Results show that the thermal system successfully reduced the surface temperature of the solar module from 88℃to as low as 55℃.Accordingly,the output power that has been decreased from 14.89 W to 10.69 W can be restored by 30.2%to achieve 13.92 W.On the other hand,the outlet water from this hydronic system reaches 45.4℃which can be used to partially heat domestic water use.Overall,this system provides a versatile framework for the design and optimization of the BIPVT systems.展开更多
Ceramic matrix composite(CMC),with higher thermal limit and lower density relative to the superalloy,is regarded as the most important structural material for modern gas turbine engines.However,the anisotropic thermal...Ceramic matrix composite(CMC),with higher thermal limit and lower density relative to the superalloy,is regarded as the most important structural material for modern gas turbine engines.However,the anisotropic thermal conductivities caused by the weave patterns totally change the thermal conduction performance inside the solid domain.Therefore,the present study aims to use the infrared thermographic to measure the SiC/SiC composite platform with staggered effusion holes along with the superalloy platform.CMC platform is prepared by 2-D plain weave braid structure with chemical vapor infiltration(CVI)process.The temperature of mainstream is 900 K to match the real mainstream to coolant temperature ratio(T_(g)/T_(c)=1.5,2.1).The experimental was conducted with seven mass flow ratios(MFR=1.5%-4.5%).The results indicate that the thermal conductivity along the thickness direction is of great importance for the CMC platform.The superalloy platform obtains higher level of overall cooling effectiveness than CMC at T_(g)/T_(c)=1.5.However,the CMC platform achieves greater overall cooling effectiveness relative to superalloy at T_(g)/T_(c)=2.1.In addition,CMC platform presents enhanced uniformity of overall cooling effectiveness due to the larger in-plane thermal conductivity.展开更多
To study the temperature distribution and thermal-stress?eld in different service stages,a twodimensional model of a turbine blade with thermal barrier coatings is developed,in which the conjugate heat transfer analys...To study the temperature distribution and thermal-stress?eld in different service stages,a twodimensional model of a turbine blade with thermal barrier coatings is developed,in which the conjugate heat transfer analysis and the decoupled thermal-stress calculation method are adopted.Based on the simulation results,it is found that a non-uniform distribution of temperature appears in different positions of the blade surface,which has directly impacted on stress?eld.The maximum temperature with a value of 1030°C occurs at the leading edge.During the steady stage,the maximum stress of thermally grown oxide(TGO)appears in the middle of the suction side,reaching 3.75 GPa.At the end stage of cooling,the maximum compressive stress of TGO with a value of -3.5 GPa occurs at the leading edge.Thus,it can be predicted that during the steady stage the dangerous regions may locate at the suction side,while the leading edge may be more prone to failure on cooling.展开更多
The overall operating cost of the modern gas turbines is greatly influenced by thedurability of hot section components operating at high temperatures.In turbine operatingconditions,some defects may occur which can dec...The overall operating cost of the modern gas turbines is greatly influenced by thedurability of hot section components operating at high temperatures.In turbine operatingconditions,some defects may occur which can decrease hot section life.In the present paper,methods used for calculating blade temperature and life are demonstrated and validated.Usingthese methods,a set of sensitivity analyses on the parameters affecting temperature and life ofa high pressure,high temperature turbine first stage blade is carried out.Investigateduncertainties are:(1)blade coating thickness,(2)coolant inlet pressure and temperature(asa result of secondary air system),and(3)gas turbine load variation.Results show thatincreasing thermal bamier coating thickness by 3 times,leads to rise in the blade life by 9times.In addition,considering inlet cooling temperature and pressure,deviation in temperaturehas greater effect on blade life.One of the interesting points that can be realized from theresults is that 300 hours operation at 70%load can be equal to one hour operation atbase load.展开更多
基金Sponsored by the National Natural Science Foundation of China( Grant No. 50576017)
文摘This paper studied a certain blade with ten radial cooling holes which employed conjugate heat transfer method. The cooling air entered the cooling channel from the bottom of the blade and went out from the top, it was not ejected into the main flow. This paper used different numerical conditions including different turbulence models,turbulence intensities,thermal conduction coefficients and the influence on fluid property via temperature variation. The temperature distribution and pressure distribution of the blade were compared with experimental data. The results show that the numerical results using different turbulence models are almost identical to experimental data even little deviation occurs at shock wave location. The trends of temperature distribution under different numerical conditions are coincident to experimental data,especially Reynolds stress turbulence model. It can be concluded that anisotropic turbulence models can simulate the transition from laminar to turbulence,and the influence of turbulence intensity on laminar region and transition region is more than that on developed turbulent region.
文摘In this paper, a 3D model of a flat circuit board with a heat generating electronic chip mounted on it has been studied numerically. The conjugate heat transfer including the conduction in the chip and convection with the surrounding fluid has been investigated numerically. Computational fluid dynamics using the finite volume method has been used for modeling the conjugate heat transfer through the chip and the circuit board. Conjugate heat transfer has broad applications in engineering and industrial applications in design of cooling off electronic components. Effects of various inlet velocities have been studied on the heat transfer variation and temperature of the circuit board. Numerical results show that the temperature of the chip reduces as the velocity of the inlet fluid flow increases.
基金National Natural Science Foundation of China(11971069,12071045)Foundation of CAEP(CX20210042)Science Challenge Project(No.TZ2016002).
文摘In this paper,we present a unified finite volume method preserving discrete maximum principle(DMP)for the conjugate heat transfer problems with general interface conditions.We prove the existence of the numerical solution and the DMP-preserving property.Numerical experiments show that the nonlinear iteration numbers of the scheme in[24]increase rapidly when the interfacial coefficients decrease to zero.In contrast,the nonlinear iteration numbers of the unified scheme do not increase when the interfacial coefficients decrease to zero,which reveals that the unified scheme is more robust than the scheme in[24].The accuracy and DMP-preserving property of the scheme are also veri ed in the numerical experiments.
基金Project supported by the National Natural Science Foundation of China(Nos.11872083,12172017,12202021)。
文摘The boiling heat transfer technology with cavity surfaces can provide higher heat flux under lower wall superheat,which is of great significance for the cooling of electronic chips and microelectromechanical devices.In this paper,the boiling characteristics of the cavity surfaces are investigated based on the lattice Boltzmann(LB)method,focusing on the effects of cavity shapes,sizes,and heater thermal conductivity on the heat transfer performance.The results show that the triangular cavity has the best boiling performance since it has less residual vapor and higher bubble departure frequency than those of the trapezoidal and rectangular cavities.As the cavity size increases,the enhancement of heat transfer by the cavity mouth is suppressed by the heat accumulation effect at the heater bottom.The liquid rewetting process during bubble departure is the reason for the fluctuation of the space-averaged heat flux,and the heater thermal conductivity determines the fluctuation amplitude.The evaporation of liquid in the cavity with high thermal conductivity walls is more intense,resulting in shorter waiting time and higher bubble departure frequency.
基金financial support from the National Natural Science Foundation of China under Grant No.51776201the National Science Foundation of Tianjin under Grant No.18JCQNJC07200。
文摘Film cooling combined with internal impingement cooling is one of the most effective technologies to protect the gas turbine vanes and blades from the hot gas. In this study, conjugate heat transfer CFD study was undertaken for a flat plate with combined film cooling and impingement cooling. An experiment on conjugate heat transfer of a flat plate with combined film and impingement cooling was performed to validate the code. Then the effects of several parameters including Biot number, blowing ratio, film hole shape and impingement hole diameter on the overall cooling effectiveness were numerically studied. The results show that for a specific combined cooling scheme and a given blowing ratio, the coolant potential can be reasonably allocated to the internal and the external cooling to achieve the overall cooling effectiveness. As the blowing ratio increases, the overall cooling effectiveness trends to reach a maximum value. For different film hole geometrical, the maximum values of the overall cooling effectiveness at high blowing ratio approximate to the same value. At a given mass flow rate of coolant, the increase of the impingement hole diameter leads to the reduction of the overall cooling effectiveness.
基金The work is financially supported by National Nature Science Foundation of China under Grant number 91130013.
文摘The preconditioned density-based conjugate heat transfer(CHT)algorithm was used to investigate the heat transfer characteristics of a cooled turbine vane.Fluid domain provided boundary heat flux for solid domain and obtained boundary temperature from it for the coupling strategy.The governing equations were solved by the preconditioned density-based finite-volume method,with preconditioning matrix,improved Abu-Gharmam Shaw(AGS)transition model,matrix dissipation scheme and four kinds of turbulence models.The grid system is multi-block structured grids for fluid domain and unstructured grids for solid domain,with full-matched grids at the fluid-solid interfaces.The effects of turbulence model,outlet Mach number,outlet Reynolds number,inlet turbulence intensity and the temperature ratio of blade surface/gas on the local heat transfer performance were studied.Results indicate that the k-o shear-stress transport(SST)and AGS model can predict the conjugate heat transfer better than others.The Mach number and Reynolds number have relatively obvious influences on the heat transfer,while the turbulence intensity and temperature ratio only have slight influences.Comparisons with experimental data demonstrate the applicability and accuracy of the numerical algorithm.
基金This study was supported by major project of National Science Foundation of China(No.61890923).
文摘Reliable transient thermal analysis plays a very important role in the engine safety analysis.Transient conjugate heat transfer simulation is an important way of temperature analysis.But there exists a great disparity in the time scales between solid conduction and fluid convection.The calculation cost of transient conjugate heat transfer analysis is very huge because of the tiny time step of computational fluid dynamics.The Bi-Fo time scaling method is proposed to improve the computational efficiency of transient conjugate heat transfer.On the one hand,this method carries out a similar transformation on solid heat conduction,scaling the calculation time with the product of density and specific heat capacity to maintain the consistency of Fourier number.On the other hand,it takes very short time for the fluid domain to recover stability after a boundary disturbance.Based on the above characteristic,the flow time is directly compressed to the same as that of the solid domain.It is verified by Mark II vane that increasing the solid thermal diffusivity can reduce the time scale of heat conduction.In the situation of rapidly stable flow field,scaling flow time does not affect the solid thermal boundary under corresponding dimensionless time.Within the application scope,the Bi-Fo time scaling method can greatly reduce the time cost of transient conjugate heat transfer simulation while maintaining the accuracy of transient temperature analysis.
基金S.Li acknowledges the support from the National Natural Science Foundation of China(NSFC)under grant No.U1930402L.Ju’s work is partially supported by U.S.National Science Foundation DMS-2109633.
文摘A unified solution framework is proposed for efficiently solving conjugate fluid and solid heat transfer problems.The unified solution is solely governed by the compressible Navier-Stokes(N-S)equations in both fluid and solid domains.Such method not only provides the computational capability for solid heat transfer simulations with existing successful N-S flow solvers,but also can relax time-stepping restrictions often imposed by the interface conditions for conjugate fluid and solid heat transfer.This paper serves as Part I of the proposed unified solution framework and addresses the handling of solid heat conduction with the nondimensional N-S equations.Specially,a parallel,adaptive high-order discontinuous Galerkin unified solver has been developed and applied to solve solid heat transfer problems under various boundary conditions.
基金This study is financially supported by the National Science and Technology Major Project(2017-III-0003-0027).
文摘By investigating heat transfer and flow structures of dimples,orthogonal ribs,and V-shaped ribs in the impingement/effusion cooling,the article is dedicated to selecting a best-performing internal cooling structure for a turbine vane.The overall cooling effectiveness and coolant consumption are adopted to evaluate the cooling performance.To analyze the influence of structural modification,the flow field is investigated on chordwise/spanwise sections and the target surface.The blockage effect on crossflow can protect jet flow,resulting in higher heat transfer performance of the target surface.Ribs own a stronger blockage effect than dimples.Compared with the blockage effect,the influence of the rib shape is negligible.By installing dimples between ribs,heat transfer is augmented further.The introduction of ribs/dimples leads to higher discharge coefficients of jet nozzles but lower discharge coefficients of film holes.Thus,the film cooling deteriorates.Meanwhile,the installation of the ribs and dimples decreases total coolant consumption.The effect of ribs/dimples on heat transfer and effusion condition of internal and external cooling is analyzed.The best-performing cooling structure is the target surface with dimples and orthogonal ribs,which decreases the wall temperature and coolant consumption by 14.57-28.03 K and 1.19%-1.81%respectively.This article concludes the flow mechanism for dimples and influence factors on the cooling performance,which may serve as guidance for the turbine vane design.
基金support from the National Natural Science Foundation of China(Grant No.:52006039)Natural Science Foundation of Guangdong Province(Grant No.:2022A1515010602)+1 种基金Guangzhou Science and Technology Plan Project(Grant No.:202201010575)Guangdong Provincial Key Laboratory of Distributed Energy Systems(Grant No.:2020B1212060075).
文摘The present study proposes a predictive model to explore the effect of partially filled porous media on the con-jugate heat transfer characteristic of phase change material(PCM)with interfacial coupling conditions between pure fluid region and porous region.The enthalpy-porosity method,local thermal non-equilibrium model and Darcy-Forchheimer law are comprehensively considered to describe the convective heat transfer process in porous media.The modified model is then validated by benchmark data provided by particle image velocimetry(PIV)ex-periments.The phase change behavior,heat transfer efficiency and energy storage performance are numerically investigated for different partial porous filling strategies in terms of filling content,position,height of porous foam and inclination angles of cavity.The results indicate that due to the resistance in porous region,the shear stress exerted by the main vortex(natural convection)in pure fluid region and the momentum transferred,a secondary vortex phenomenon appears in the porous region near the fluid/porous interface.Moreover,such dis-continuity of permeability and fluid-to-porous thermal conductivity results in the cusp of phase change interface at the horizontal fluid/porous boundary.Among four partial porous filling cases,the lower porous filling one has more desirable heat transfer performance,and the 3/4H lower porous filling configuration is the best solution for optimization of the latent heat thermal energy storage(LHTES)systems.For tilted cavity,the increase of inclination angle positively affects the heat transfer efficiency as well as the energy storage rate of the LHTES system,where the performance of 3/4H lower porous filling configuration is further highlighted.
基金supported by the National Natural Science Foundation of China(Project Nos.51934004,51674158,51574158,and 51474106)the Major Program of Shandong Province Natural Science Foundation(ZR2018ZA0602)+2 种基金the Taishan Scholar Talent Team Support Plan for Advantaged&Unique Discipline Areasthe Science and technology support plan for Youth Innovation of colleges and universities in Shandong Province(2019KJH006)the special funds for Taishan scholar project(TS20190935)。
文摘To study the seepage and deformation characteristics of coal at high temperatures,coal samples from six different regions were selected and subjected to computed tomography(CT)scanning studies.In conjunction with ANSYS software,3 D reconstruction of CT images was used for the establishment of fluidsolid conjugate heat transfer model and coal thermal deformation model based on the microstructures of coal.In addition,the structure of coal was studied in 2 D and 3 D perspectives,followed by the analysis of seepage and deformation characteristics of coal at high temperatures.The results of this study indicated that porosity positively correlated with the fractal dimension,and the connectivity and seepage performances were roughly identical from 2 D and 3 D perspectives.As the porosity increased,the fractal dimension of coal samples became larger and the pore-fracture structures became more complex.As a result,the permeability of coal samples decreased.In the meantime,fluid was fully heated,generating high-temperature water at outlet.However,when the porosity was low,the outlet temperature was very high.The average deformation of coal skeleton with different pore-fracture structures at high temperatures showed a trend of initial increase and subsequent decrease with the increase of porosity and fractal dimension.The maximum deformation of coal skeleton positively correlated with connectivity but negatively correlated with the fractal dimension.
基金Supported by the National Natural Science Foundation of China(51677104)。
文摘Focusing on the design problem of high-performance radiators for planar motors in the wafer stage of the lithography machine,a thermal-fluid coupling optimization scheme based on parametric solid components was proposed.The mapping method between component parameters and pseudo-density values was established.An analytical solution for the sensitivity of pseudo-density to component parameters was given.The conjugate heat transfer function with the shallow channel approximation term was solved through the pseudo-density information.In the optimization example,circular components were selected,and the position and the size of solid components were chosen as design variables.In order to eliminate calculation errors caused by pseudo-density,an optimized pseudo-density field was converted into the result based on parametric components.Compared to the reference motor radiator,the average surface temperature rise of the optimized water-cooling motor radiator is reduced by 22.4%,which verifies the feasibility and effectiveness of the proposed method.
基金Sponsored by the National Natural Science Foundation of China(Grant No. 50476028)
文摘This paper implemented cooling configuration design on certain gas turbine HP rotor using parameterized method.It is convenient for complicated gas turbine blade modeling using parameters and also benefit for the geometry modify in later period.Parameterized modeling is the foundation of air cooling turbine blade design method engineering application.Mesh quality can be awarded when generated complicated cooling configuration blade grids,and also the increase of calculation error can arise by many mesh blocks.Film cooling and serpentine passage can effectively enhance the cooling effectiveness and protect blade.
基金supported by National Science and Technology Major Project (Grand No. J2019-IV-0006-0074)National Science and Technology Major Project (Grand No. J2019-Ⅱ-0010-0030)。
文摘As turbine inlet temperature gets higher and higher,thermal barrier coating(TBC) is more and more widely used in turbine blades.For turbine blades with TBC,it is of great significance to evaluate the temperature distribution of its substrate metal quickly and accurately,especially during the design stage.With different degrees of simplification such as whether to consider the change of the geometric size of the fluid domain by TBC and whether to consider the planar heat conduction in TBC,three different methods used in conjugate heat transfer(CHT) simulation to model the TBC of the turbine blades have been developed and widely used by researchers.However,little research has been conducted to investigate the influence of the three methods on the temperature distribution of turbine blade.To fill this gap,three geometric models were designed.They are a solid conduction model with a substrate metal layer and a TBC layer,a transonic turbine vane with internal cooling and TBC,and a plate cylindrical film hole cooling model with TBC.Different methods were used in these geometric models and their differences were carefully analyzed and discussed.The result shows that for the conduction model used in this paper,with the same TBC surface temperature distribution,the difference between the three methods is very small and can be ignored.For a transonic turbine vane with internal cooling,regarding the local maximum temperature of the substrate-TBC interface,the largest difference between the method in which TBC is considered as a thermal resistance or a virtual layer of cells and the method in which three-dimensional heat conduction equation of TBC is solved occurs at the trailing edge.The difference near the leading edge is below 2K.When employed to the film cooling model,the difference of the laterally averaged temperature of the substrate-TBC interface can be 8 K which is mainly due to the change of the length to diameter ratio of the film cooling hole by TBC.If the substrate thickness is reduced by the thickness of TBC when three-dimensional heat conduction equation of TBC is solved,the temperature difference between the three methods will be quite limited.
文摘Great efforts are still put into the design process of advanced film-cooling configurations.In particular,the vanes and blades of turbine front stages have to be cooled extensively for a safe operation.The conjugate calculation technique is used for the three dimensional thermal load prediction of a fim-cooled test blade of a modern gas turbine.Thus,it becomes possible to take into account the interaction of internal flows,external flow,and heat transfer without the prescription of heat transfer ooefficients.The focus of the investigation is laid on the leading edge part of the blade.The numerical model consists of all internal flow passages and cooling hole rows at the leading edge.Furthermore,the radial gap flow is also part of the model.The comparison with thermal pyrometer measurements shows that with respect to regions with high thermal load a qualitatively and quantitatively good agreement of the conjugate results and the measurements can be found.In particular,the region in the vicinity of the mid-span section is exposed to a higher thermal load,which requires further improvement of the cooling arrangement.Altogether the achieved results demonstrate that the conjugate calculation technique is applicable for reasonable prediction of three-dimensional thermal load of complex cooling configurations for blades.
基金This publication has emanated from research supported in part by a grant from Science Foundation Ireland(No.15/RP/B3208)The acknowledgment also goes to the“111”Project by the State Administration of Foreign Experts Affairs and the Ministry of Education of China(No.B07014).
文摘Conjugate heat transfer is numerically investigated using a three-dimensional computational fluid dynamics approach in various microchannel geometries to identify a high-performance cooling method for piezoelectric ceramic stacks and spindle units in high-precision machines.Straight microchannels with rectangular cross sections are first considered,showing the performance limitations of decreasing the size of the microchannels,so other solutions are needed for high applied heat fluxes.Next,many microchannel designs,focusing on streamwise geometric variation,are compared to straight channels to assess their performances.Sinusoidally varying channels produce the highest heat transfer rates of those studied.Thus,their optimization is considered at a channel width and height of 35 and 100μm,respectively.Heat transfer increases as the amplitude and spatial frequencies of the channels increase due to increased interfacial surface area and enhanced Dean flow.The highest performance efficiencies are observed at intermediate levels of amplitude and frequency,with efficiency decreasing as these geometric parameters are increased further at the onset of flow separation.The sinusoidal channel geometries are then optimized with respect to minimizing the system’s pressure drop for all applied heat fluxes between 5690 and 6510 kW/m2.Doing so created an optimal geometry curve and showed that all geometries in this region had amplitudes close to 40μm.Therefore,imposing a fixed heat flux requirement for a case study of cooling piezoelectric ceramics,the optimized sinusoidal geometry decreases the system pressure drop by 79%relative to a straight channel while maintaining a larger minimum feature size.
基金the National Science Foundation IIP#1941244,CMMI#1762891U.S.Department of Agriculture NIFA#2021-67021-34201,whose support is gratefully acknowledged.
文摘A novel building integrated photovoltaic thermal(BIPVT)roofing panel has been designed considering both solar energy harvesting efficiency and thermal performance.The thermal system reduces the operating temperature of the cells by means of a hydronic loop integrated into the backside of the panel,thus resulting in maintaining the efficiency of the solar panels at their feasible peak while also harvesting the generated heat for use in the building.The performance of the proposed system has been evaluated using physical experiments by conducting case studies to investigate the energy harvesting efficiency,thermal performance of the panel,and temperature differences of inlet/outlet working liquid with various liquid flow rates.The physical experiments have been simulated by coupling the finite element method(FEM)and finite volume method(FVM)for heat and mass transfer in the operation.Results show that the thermal system successfully reduced the surface temperature of the solar module from 88℃to as low as 55℃.Accordingly,the output power that has been decreased from 14.89 W to 10.69 W can be restored by 30.2%to achieve 13.92 W.On the other hand,the outlet water from this hydronic system reaches 45.4℃which can be used to partially heat domestic water use.Overall,this system provides a versatile framework for the design and optimization of the BIPVT systems.
基金support of National Natural Science Foundation of China(No.52006178)National Key R&D Program of China(No.Y2019-Ⅷ-0007-0168)+1 种基金the Fundamental Research Funds for the Central Universitiesthe Innovation Capacity Support Plan in Shaanxi Province of China(Grant No.2023-CX-TD-19)。
文摘Ceramic matrix composite(CMC),with higher thermal limit and lower density relative to the superalloy,is regarded as the most important structural material for modern gas turbine engines.However,the anisotropic thermal conductivities caused by the weave patterns totally change the thermal conduction performance inside the solid domain.Therefore,the present study aims to use the infrared thermographic to measure the SiC/SiC composite platform with staggered effusion holes along with the superalloy platform.CMC platform is prepared by 2-D plain weave braid structure with chemical vapor infiltration(CVI)process.The temperature of mainstream is 900 K to match the real mainstream to coolant temperature ratio(T_(g)/T_(c)=1.5,2.1).The experimental was conducted with seven mass flow ratios(MFR=1.5%-4.5%).The results indicate that the thermal conductivity along the thickness direction is of great importance for the CMC platform.The superalloy platform obtains higher level of overall cooling effectiveness than CMC at T_(g)/T_(c)=1.5.However,the CMC platform achieves greater overall cooling effectiveness relative to superalloy at T_(g)/T_(c)=2.1.In addition,CMC platform presents enhanced uniformity of overall cooling effectiveness due to the larger in-plane thermal conductivity.
基金supported by the National Natural Science Foundation of China(Grant Nos.51172192,11272275 and 11002122)the Natural Science Foundation of Hunan Province(Grant No.11JJ4003)the Doctoral Scientific Research Foundation of Xiangtan University(Grant Nos.KZ08022,KZ03013 and KF20140303)
文摘To study the temperature distribution and thermal-stress?eld in different service stages,a twodimensional model of a turbine blade with thermal barrier coatings is developed,in which the conjugate heat transfer analysis and the decoupled thermal-stress calculation method are adopted.Based on the simulation results,it is found that a non-uniform distribution of temperature appears in different positions of the blade surface,which has directly impacted on stress?eld.The maximum temperature with a value of 1030°C occurs at the leading edge.During the steady stage,the maximum stress of thermally grown oxide(TGO)appears in the middle of the suction side,reaching 3.75 GPa.At the end stage of cooling,the maximum compressive stress of TGO with a value of -3.5 GPa occurs at the leading edge.Thus,it can be predicted that during the steady stage the dangerous regions may locate at the suction side,while the leading edge may be more prone to failure on cooling.
文摘The overall operating cost of the modern gas turbines is greatly influenced by thedurability of hot section components operating at high temperatures.In turbine operatingconditions,some defects may occur which can decrease hot section life.In the present paper,methods used for calculating blade temperature and life are demonstrated and validated.Usingthese methods,a set of sensitivity analyses on the parameters affecting temperature and life ofa high pressure,high temperature turbine first stage blade is carried out.Investigateduncertainties are:(1)blade coating thickness,(2)coolant inlet pressure and temperature(asa result of secondary air system),and(3)gas turbine load variation.Results show thatincreasing thermal bamier coating thickness by 3 times,leads to rise in the blade life by 9times.In addition,considering inlet cooling temperature and pressure,deviation in temperaturehas greater effect on blade life.One of the interesting points that can be realized from theresults is that 300 hours operation at 70%load can be equal to one hour operation atbase load.
