A solid-phase sintering process for the low-cost fabrication of composite micro-channels was developed. Three kinds of composite micro-channels with metallic porous structures were designed. The sintering process was ...A solid-phase sintering process for the low-cost fabrication of composite micro-channels was developed. Three kinds of composite micro-channels with metallic porous structures were designed. The sintering process was studied and optimized to obtain porous-structured micro-channels with high porosity. The flow resistance and heat transfer performance in the composite micro-channels were investigated. The composite micro-channels show acceptable flow resistance, significant enhancement of heat transfer and dramatic improvement of flow boiling stability, which indicates a promising prospect for the application in forced convective heat transfer.展开更多
The heat transfer features around the elliptic cylinder of axis ratio 4∶1 in crossflow were investigated experimentally within a wide range of Reynolds number. By means of heat-mass transfer analogy and the naphthale...The heat transfer features around the elliptic cylinder of axis ratio 4∶1 in crossflow were investigated experimentally within a wide range of Reynolds number. By means of heat-mass transfer analogy and the naphthalene sublimation technique, the local heat transfer distribution and the mean heat transfer coefficient are clarified. The result shows that the mean heat transfer coefficient is higher than that of a circular cylinder in most Reynolds number range regarded, and this superiority turns to be more significant with the increase of flow speed. Moreover, the effect of axis ratio on mean heat transfer coefficient was investigated tentatively. The oil-lampblack technique was employed to enable visualization of the flow pattern around the cylinder and on the cylinder wall.展开更多
In this study, laminar convective heat transfer over two heated wall-mounted cubes is investigated.Two cubes, which are under constant heat flux, are placed in different tandem and staggeredarrangements ...In this study, laminar convective heat transfer over two heated wall-mounted cubes is investigated.Two cubes, which are under constant heat flux, are placed in different tandem and staggeredarrangements on a base plate. This problem is studied for different streamwise and spanwisedistances between two cubes in different Renolds number (Re), by using finite-volume method.Effects of these parameters are considered on flow and heat transfer characteristics. The resultsshow that the temperature distribution is strongly dependent on flow structure and varies with anychange of flow pattern in different arrangements of cubes. In addition, it is observed that the dragcoefficient, which is influenced more by pressure forces, in staggered arrangement, is greater thantandem arrangement. Results show that by increasing the spanwise distance the amount of meanNusselt number (Nu) of Cube 2 becomes the same as Cube 1.展开更多
Forced convective experiment of supercritical water was performed in Inconel-625 tubes of 4.62 mm, 7.98 mm and 10.89 mm in diameter. The water flowed upward, covering the ranges of pressure of 23.4 MPa to 25.8 MPa, ma...Forced convective experiment of supercritical water was performed in Inconel-625 tubes of 4.62 mm, 7.98 mm and 10.89 mm in diameter. The water flowed upward, covering the ranges of pressure of 23.4 MPa to 25.8 MPa, mass flux of 90 kg/m^2s to 3,281 kg/m^2s, local bulk temperature of 102-384 ℃, inner wall temperature of 167-669℃ and heat flux of up to 2.41 MW/m^2. The results exhibited severe deteriorated and enhancement heat transfer. The experimental results can be calculated by the Jackson's correlation and the Bishop's correlation mostly. But some data with strong effects of the buoyancy force and the variations of flow regimes can not be predicted properly.展开更多
Experiments were carried out to study the heat transfer performance of an impinging jet in a cross flow.Several parameters including the jet-to-cross-flow mass ratio(X=2%-8%), the Reynolds number(Red=1434-5735)and the...Experiments were carried out to study the heat transfer performance of an impinging jet in a cross flow.Several parameters including the jet-to-cross-flow mass ratio(X=2%-8%), the Reynolds number(Red=1434-5735)and the jet diameter(d=2-4 mm) were explored. The heat transfer enhancement factor was found to increase with the jet-to-cross-flow mass ratio and the Reynolds number, but decrease with the jet diameter when other parameters maintain fixed. The presence of a cross flow was observed to degrade the heat transfer performance in respect to the effect of impinging jet to the target surface only. In addition, an impinging jet was confirmed to be capable of enhancing the heat transfer process in considerable amplitude even though the jet was not designed to impinge on the target surface.展开更多
In order to improve the convective heat transfer relating to an eddy current retarder,the finite element model has been used to assess the performances of different possible designs.In particular,assuming the steady r...In order to improve the convective heat transfer relating to an eddy current retarder,the finite element model has been used to assess the performances of different possible designs.In particular,assuming the steady running state of retarder as the working condition,flow and temperature fields have been obtained for the rotor.The influence of airflow path on heat dissipation has been analysed,and the influence of the temperature field distribution on the performance of retarder has been discussed accordingly.The results show that when the steady running state of the turntable is considered,the maximum temperature is lower,the level of turbulence flow is mitigated,and the temperature distribution becomes more regular.These factors contribute to improve the heat dissipation ability of the retarder.展开更多
A compressible lattice Boltzmann-finite difference method is extended by the phase-field approach into a monolithic scheme to study fluid flow and heat transfer through regular arrangements of solid bodies of circular...A compressible lattice Boltzmann-finite difference method is extended by the phase-field approach into a monolithic scheme to study fluid flow and heat transfer through regular arrangements of solid bodies of circular,elliptical and irregular shapes.The advantage of using the phase-field method is demon-strated both in its simplicity of accounting for flow and thermal boundary conditions at solid surfaces with irregular shapes and in the capability of generating such complex-shaped objects.For an array of discs,numerical results for the overall solid-to-gas heat transfer rate are validated via experiments on flow through arrays of hot cylinders.The thus validated compressible LB-FD-PF hybrid scheme is used to study the dependence of heat transfer on flow and thermal boundary conditions(Reynolds number,temperature difference between the hot solid bodies and the inlet gas),porosity as well as on the shape of solid objects.Results are rationalized in terms of the residence time of the gas close to the solid body and downstream variations of gas velocity and temperature.Perspective for further applications of the proposed methodology are also discussed.展开更多
In this paper,characteristics of flow and convective heat transfer of China RP-3 kerosene in straight circular pipe were numerically studied.Navier-Stokes equations were solved using RNG k-turbulence model with low Re...In this paper,characteristics of flow and convective heat transfer of China RP-3 kerosene in straight circular pipe were numerically studied.Navier-Stokes equations were solved using RNG k-turbulence model with low Reynolds number correction.The thermophysical and transport properties of the China RP-3 kerosene were calculated with a 10-species surrogate and the extended corresponding state method(ECS) combined with Benedict-Webb-Rubin equation.The independence of grids was first studied and the numerical results were then compared with experimental data for validation.Under flow conditions given in the paper,the results show that deterioration of convective heat transfer occurs when the wall temperature is slightly higher than the pseudo-critical temperature of kerosene for cases with wall heat flux of 1.2 and 0.8 MW/m 2.The degree of the heat transfer deterioration is weakened as the heat flux decreases.The deterioration,however,does not happen when the heat flux on the pipe wall is reduced to 0.5 MW/m 2.Based on the analysis of the near-wall turbulent properties,it is found that the heat transfer deterioration and then the enhancement are attributed partly to the change in the turbulent kinetic energy in the vicinity of pipe wall.The conventional heat transfer relations such as Sieder-Tate and Gnielinski formulas can be used for the estimation of kerosene heat convection under subcritical conditions,but they are not capable of predicting the phenomenon of heat transfer deterioration.The modified Bae-Kim formula can describe the heat transfer deterioration.In addition,the frictional drag would increase dramatically when the fuel transforms to the supercritical state.展开更多
Topology optimization of simplified convective heat transfer has been widely studied,but most existing studies are based on the finite element method(FEM);methods based on the finite volume method(FVM)have been less s...Topology optimization of simplified convective heat transfer has been widely studied,but most existing studies are based on the finite element method(FEM);methods based on the finite volume method(FVM)have been less studied.In this paper,a topology optimization method based on FVM was proposed for a simplified convective heat transfer problem.We developed a novel adjoint sensitivity analysis method applicable to FVM,which included adjoint equations,corresponding boundary conditions,and sensitivity analysis equations.Additionally,a program for the proposed topology optimization method was developed in open field operation and manipulation(OpenFOAM)and portable,extensibletoolkit for scientific computation(PETSc).Thus,large-scale topology optimizations could be performed in parallel.Furthermore,numerical examples of the classical two-dimensional(2D)and 3D optimization problems were considered.The results verified the effectiveness and feasibility of the proposed method.The results of large-scale 3D examples show an interesting phenomenon that for the optimized designs with few features,the large-scale topology optimization is still valuable for obtaining more effective structural shapes.展开更多
The present study concerns the measurement of the convective heat transfer coefficient on the solid-fluid interface by the pulsed photothermal method.This non-intrusive technique is apphed for the measurement of the l...The present study concerns the measurement of the convective heat transfer coefficient on the solid-fluid interface by the pulsed photothermal method.This non-intrusive technique is apphed for the measurement of the local heat transfer coefficients in cooling of a rectangular slab that simulates an electronic component.The heat transfer coefficient is deduced from the evolution of the transient temperature induced by a sudden deposit of a luminous energy on the front face of the slab.In order to draw up the heat transfer cartography by a non-destructive tool, the infrared thermography has been used.Two inverse techniques for the identification of the heat transfer coefficient are presented here.The first one is based on the assumption that heat transfer coefficient remains constant during the pulsed experiment,and the second one considered it variable in space and time.The temporal and spatial evolutions are expressed as a constant heat transfer coefficient(h_0)multiplied by a function of time and space f(x,t).The function f is deduced from the resolution of the conjugated convection-conduction problem,by a control volume technique for the case of thermally thick sample.The results are given for different air velocities and deflection angles of the flow.展开更多
This paper is concerned with the forced convective heat transfer of dilute liquid suspensions of nanoparticles (nanofluids) flowing through a straight pipe under laminar conditions. Stable nanofluids are formulated ...This paper is concerned with the forced convective heat transfer of dilute liquid suspensions of nanoparticles (nanofluids) flowing through a straight pipe under laminar conditions. Stable nanofluids are formulated by using the high shear mixing and ultrasonication methods. They are then characterised for their size, surface charge,thermal and rheological properties and tested for their convective heat transfer behaviour. Mathematical modelling is performed to simulate the convective heat transfer of nanofluids using a single phase flow model and considering nanofluids as both Newtonian and non-Newtonian fluid. Both experiments and mathematical modelling show that nanofluids can substantially enhance the convective heat transfer. Analyses of the results suggest that the non-Newtonian character of nanofluids influences the overall enhancement, especially for nanofluids with an obvious non-Newtonian character.展开更多
In this study, exergy efficiency is defined to evaluate convective heat transfer in a tube based on the local exergy destruction rate from the equilibrium equation of available potential. By calculating this destructi...In this study, exergy efficiency is defined to evaluate convective heat transfer in a tube based on the local exergy destruction rate from the equilibrium equation of available potential. By calculating this destruction rate, the local irreversibility of convective heat transfer can be evaluated quantitatively. The exergy efficiency and distribution of local exergy destruction rate for a smooth tube, an enhanced tube into which short-width twisted tape has been inserted, and an optimized tube with exergy destruction minimization are analyzed by solving the governing equations through a finite volume method(FVM). For the smooth tube, the exergy efficiency increases with increasing Reynolds number(Re) and decreases as the heat flux increases, whereas the Nusselt number(Nu) remains constant. For the enhanced tube, the exergy efficiency increases with increasing Reynolds number and increases as the short-width rate(w) increases. An analysis of the distribution of the local exergy destruction rate for a smooth tube shows that exergy destruction in the annular region between the core flow and tube wall is the highest. Furthermore, the exergy destruction for the enhanced and optimized tubes is reduced compared with that of the smooth tube. When the Reynolds number varies from 500 to 1750, the exergy efficiencies for the smooth, enhanced, and optimized tubes are in the ranges 0.367–0.485, 0.705–0.857, and 0.885–0.906, respectively. The results show that exergy efficiency is an effective evaluation criterion for convective heat transfer and the distribution of the local exergy destruction rate reveals the distribution of local irreversible loss. Disturbance in the core flow can reduce exergy destruction, and improve the exergy efficiency as well as heat transfer rate. Besides, optimization with exergy destruction minimization can provide effective guidance to improve the technology of heat transfer enhancement.展开更多
The entransy theory is widely used and found to be effective in thermal analyses and optimizations.Some researchers considered the entransy variation due to viscous heating as part of entransy dissipation and analyzed...The entransy theory is widely used and found to be effective in thermal analyses and optimizations.Some researchers considered the entransy variation due to viscous heating as part of entransy dissipation and analyzed convective heat transfer based on the differential relationship between entropy and entransy.However,it has been pointed out that the derivation of the differential relationship between entropy and entransy is incorrect.In this paper,the convective heat transfer processes with viscous heating is reconsidered and analyzed from the viewpoint of the energy conservation and the entransy balance equation.It is shown that the influence of the viscous heating is equivalent to that of an inner heat source.Therefore,the contribution of viscous heating to system entransy should not be treated as part of entransy dissipation,but entransy flow into the system.Two-stream parallel and counter flow heat exchangers with viscous heating and a thermal insulation transportation problem of heavy oil are taken as examples to verify the theoretical analyses intuitively.In the examples,the numerical results show that the entransy dissipation rates could be negative when the influence of the viscous heating on the system entransy is treated as part of the entransy dissipation.This is obviously unreasonable.Meanwhile,when the entransy contribution from the viscous heating to the system entransy is treated as entransy flow into the system,it is shown that the entransy dissipation rate is always positive,and the heat transfer processes can be well explained with the entransy theory.展开更多
A significant way to achieve energy saving and emission reduction is to optimize the design of heat transfer devices.As is widely applied in industry,a corrugated tube constructed by B-spline curve is numerically inve...A significant way to achieve energy saving and emission reduction is to optimize the design of heat transfer devices.As is widely applied in industry,a corrugated tube constructed by B-spline curve is numerically investigated and the profile is optimized,using a surrogate model with considerations of performance evaluation criterion(PEC)as single objective or minimum flow resistance(f)and maximum Nusselt number(Nu)as multi-objective.The machine learning technique is used to determine the candidate samples to update the surrogate model for improving the optimization efficiency and reliability,which is validated to be effective in this paper.The optimization results show that the comprehensive performance of the corrugated tube is more sensitive to the vertical coordinates of the control points,with the appropriate increase in the number of control points for Bspline,and the better performance of corrugated tubes is achieved.The optimal profile corresponding to the best comprehensive performance is a double-crest shape.With Reynolds number(Re)increased,the wave-amplitude of the first wave gradually gets smaller,and the profile of the corrugated tube becomes smoother.With the increasing consideration of heat transfer performance over multi-objective optimization,the optimal shape gradually changes from a double-trough to a single-trough shape.Finally,the maximum PEC of 1.2415,1.1845,and 1.1504 are acquired with the Re=8000,10000,and 12000,respectively,and the maximum Nu increases from 358.540 to 478.821.Compared with the design with the maximum thermal performance,the best compromise solution from multi-objective optimization is determined at Re=8000,10000,and 12000,showing improved flow resistance of 83.917%,85.465%,and 84.473%,but with sacrificed thermal performance of 36.754%,37.088%,and 35.005%,respectively.展开更多
A parabolic trough solar collector(PTSC)converts solar radiation into thermal energy.However,low thermal efficiency of PTSC poses a hindrance to the deployment of solar thermal power plants.Thermal performance of PTSC...A parabolic trough solar collector(PTSC)converts solar radiation into thermal energy.However,low thermal efficiency of PTSC poses a hindrance to the deployment of solar thermal power plants.Thermal performance of PTSC is enhanced in this study by incorporating magnetic nanoparticles into the working fluid.The circular receiver pipe,with dimensions of 66 mm diameter,2 mm thickness,and 24 m length,is exposed to uniform temperature and velocity conditions.The working fluid,Therminol-66,is supplemented with Fe3O4 magnetic nanoparticles at concentrations ranging from 1%to 4%.The findings demonstrate that the inclusion of nanoparticles increases the convective heat transfer coefficient(HTC)of the PTSC,with higher nanoparticle volume fractions leading to greater heat transfer but increased pressure drop.The thermal enhancement factor(TEF)of the PTSC is positively affected by the volume fraction of nanoparticles,both with and without a magnetic field.Notably,the scenario with a 4%nanoparticle volume fraction and a magnetic field strength of 250 G exhibits the highest TEF,indicating superior thermal performance.These findings offer potential avenues for improving the efficiency of PTSCs in solar thermal plants by introducing magnetic nanoparticles into the working fluid.展开更多
An exact analytical solution is obtained for convective heat transfer in straight ducts with rectangular cross-sections for the first time.This solution is valid for both H1 and H2 boundary conditions,which are relate...An exact analytical solution is obtained for convective heat transfer in straight ducts with rectangular cross-sections for the first time.This solution is valid for both H1 and H2 boundary conditions,which are related to fully developed convective heat transfer under constant heat flux at the duct walls.The separation of variables method and various other mathematical techniques are used to find the closed form of the temperature distribution.The local and mean Nusselt numbers are also obtained as functions of the aspect ratio.A new physical constraint is presented to solve the Neumann problem in non-dimensional analysis for the H2 boundary conditions.This is one of the major innovations of the current study.The analytical results indicate a singularity occurs at a critical aspect ratio of 2.4912 when calculating the local and mean Nusselt numbers.展开更多
Forced convective heat transfer in a plate channel filled with metallic spherical particles was investigated experimentally and numerically. The test section, 58 mm×80mm×5mm in size, was heated by a 0.4 mm t...Forced convective heat transfer in a plate channel filled with metallic spherical particles was investigated experimentally and numerically. The test section, 58 mm×80mm×5mm in size, was heated by a 0.4 mm thick plate electrical heater. The coolant water now rate ranged from 0.015 to 0.833 kg/s.The local wall temperature distribution was measured along with the inlet and outlet fluid temperatures and pressures. The results illustrate the heat transfer augmentation and increased pressure drop caused by the porous medium. The heat transfer coefficient was increased 5-12 times by the porous media although the hydraulic resistance was increased even more. The Nusselt number and the heat transfer coefficient increased with decreasing particIe diameter, while the pressure drop decreased as the particle diameter increased. It was found that, for the conditions studied (metallic packed bed),the effect of thermal dispersion did not need to be considered in the physical model, as opposed to a non-metallic packed bed, where thermal dispersion is important.展开更多
Convective heat transfer coefficient is one of the most vital parameters which reveals the thermal efficiency of a pipe flow.To obtain such coefficients for problems with variable pipe wall temperature,numerical itera...Convective heat transfer coefficient is one of the most vital parameters which reveals the thermal efficiency of a pipe flow.To obtain such coefficients for problems with variable pipe wall temperature,numerical iterative methods should be used which could be time-consuming and less accurate.In this paper,thermophysical properties of fluids are assumed to be constant.We define a variable related to the temperature gradient of the pipe wall and study the varying law of the local coefficient.Then,a sample-based scheme is proposed to avoid the calculation of a time-consuming problem in the use of solutions with low computing cost.To verify its accuracy,several problems in normal circle pipes with variable factors,such as the various temperatures of the pipe wall,the different radius of the pipe,and various velocities of fluid flow,are well resolved.Meanwhile,its validity in a convergent pipe is also studied.From the obtained results,the high accuracy and efficiency of the proposed scheme can be confirmed.Therefore,the proposed scheme for determining the convective heat transfer coefficient has great potential in engineering problems.展开更多
During the past six years comprehensive research programs have been conducted at the Beijing Polytechnic University to provide a better understanding of heat transfer characteristics of existing and condidate cool- in...During the past six years comprehensive research programs have been conducted at the Beijing Polytechnic University to provide a better understanding of heat transfer characteristics of existing and condidate cool- ing techniques for electronic and microelectronic devices.This paper provides a review and summary of the programs with emphasis on direct liquid cooling.Included in this review are the heat transfer investigations related to the following cooling modes:liquid free,mixed and forced convection,liquid jet impingement,flowing liquid film cooling,pool boiling,spray cooling,foreign gas jet impingement in liquid pool,and forced convection air-cooling.展开更多
Convective heat transfer and radiative heat transfer are two essential heat transfer modes in the heating process of steel;it is important to understand the role of them during the heating process clearly.The effects ...Convective heat transfer and radiative heat transfer are two essential heat transfer modes in the heating process of steel;it is important to understand the role of them during the heating process clearly.The effects of the convective and radiative heat transfer during the heating process of a cast ingot in a tubular furnace have been studied by the designed natural and forced convection experiments and mathematical simulations.The heating time for the center of the ingot to reach the furnace temperature is decreased with the increase in furnace temperature.According to the experimental and simulation results,a model is proposed regarding the role of radiative and convective heat transfer in the heating process.At low temperature,the convective heat transfer plays a dominant role,while at high temperature,the influence of radiative heat transfer is larger.And a critical temperature exists between them.The forced convective heat transfer can enhance the influence of the convective heat transfer.The critical temperature can be shifted to higher temperatures.展开更多
基金Project(51146010)supported by the National Natural Science Foundation of ChinaProject(S2011040003189)supported by the Doctoral Research Fund of Guangdong Natural Science Foundation,ChinaProject supported by the Fundation of Key Laboratory of Surface Functional Structure Manufacturing of Guangdong Higher Education Institutes,South China University of Technology
文摘A solid-phase sintering process for the low-cost fabrication of composite micro-channels was developed. Three kinds of composite micro-channels with metallic porous structures were designed. The sintering process was studied and optimized to obtain porous-structured micro-channels with high porosity. The flow resistance and heat transfer performance in the composite micro-channels were investigated. The composite micro-channels show acceptable flow resistance, significant enhancement of heat transfer and dramatic improvement of flow boiling stability, which indicates a promising prospect for the application in forced convective heat transfer.
文摘The heat transfer features around the elliptic cylinder of axis ratio 4∶1 in crossflow were investigated experimentally within a wide range of Reynolds number. By means of heat-mass transfer analogy and the naphthalene sublimation technique, the local heat transfer distribution and the mean heat transfer coefficient are clarified. The result shows that the mean heat transfer coefficient is higher than that of a circular cylinder in most Reynolds number range regarded, and this superiority turns to be more significant with the increase of flow speed. Moreover, the effect of axis ratio on mean heat transfer coefficient was investigated tentatively. The oil-lampblack technique was employed to enable visualization of the flow pattern around the cylinder and on the cylinder wall.
文摘In this study, laminar convective heat transfer over two heated wall-mounted cubes is investigated.Two cubes, which are under constant heat flux, are placed in different tandem and staggeredarrangements on a base plate. This problem is studied for different streamwise and spanwisedistances between two cubes in different Renolds number (Re), by using finite-volume method.Effects of these parameters are considered on flow and heat transfer characteristics. The resultsshow that the temperature distribution is strongly dependent on flow structure and varies with anychange of flow pattern in different arrangements of cubes. In addition, it is observed that the dragcoefficient, which is influenced more by pressure forces, in staggered arrangement, is greater thantandem arrangement. Results show that by increasing the spanwise distance the amount of meanNusselt number (Nu) of Cube 2 becomes the same as Cube 1.
文摘Forced convective experiment of supercritical water was performed in Inconel-625 tubes of 4.62 mm, 7.98 mm and 10.89 mm in diameter. The water flowed upward, covering the ranges of pressure of 23.4 MPa to 25.8 MPa, mass flux of 90 kg/m^2s to 3,281 kg/m^2s, local bulk temperature of 102-384 ℃, inner wall temperature of 167-669℃ and heat flux of up to 2.41 MW/m^2. The results exhibited severe deteriorated and enhancement heat transfer. The experimental results can be calculated by the Jackson's correlation and the Bishop's correlation mostly. But some data with strong effects of the buoyancy force and the variations of flow regimes can not be predicted properly.
基金Supported by the National Natural Science Foundation of China(51106140)the Natural Science Foundation of Zhejiang Province(Z1110695)
文摘Experiments were carried out to study the heat transfer performance of an impinging jet in a cross flow.Several parameters including the jet-to-cross-flow mass ratio(X=2%-8%), the Reynolds number(Red=1434-5735)and the jet diameter(d=2-4 mm) were explored. The heat transfer enhancement factor was found to increase with the jet-to-cross-flow mass ratio and the Reynolds number, but decrease with the jet diameter when other parameters maintain fixed. The presence of a cross flow was observed to degrade the heat transfer performance in respect to the effect of impinging jet to the target surface only. In addition, an impinging jet was confirmed to be capable of enhancing the heat transfer process in considerable amplitude even though the jet was not designed to impinge on the target surface.
基金supported by Scientific and Technological Research Program of Chongqing Municipal Education Commission(Grant No.KJ1603004).
文摘In order to improve the convective heat transfer relating to an eddy current retarder,the finite element model has been used to assess the performances of different possible designs.In particular,assuming the steady running state of retarder as the working condition,flow and temperature fields have been obtained for the rotor.The influence of airflow path on heat dissipation has been analysed,and the influence of the temperature field distribution on the performance of retarder has been discussed accordingly.The results show that when the steady running state of the turntable is considered,the maximum temperature is lower,the level of turbulence flow is mitigated,and the temperature distribution becomes more regular.These factors contribute to improve the heat dissipation ability of the retarder.
基金funded by the Deutsche For-schungsgemeinschaft(DFG,German Research Foundation)-422037413-CRC/TRR 287"BULK-REACTION".
文摘A compressible lattice Boltzmann-finite difference method is extended by the phase-field approach into a monolithic scheme to study fluid flow and heat transfer through regular arrangements of solid bodies of circular,elliptical and irregular shapes.The advantage of using the phase-field method is demon-strated both in its simplicity of accounting for flow and thermal boundary conditions at solid surfaces with irregular shapes and in the capability of generating such complex-shaped objects.For an array of discs,numerical results for the overall solid-to-gas heat transfer rate are validated via experiments on flow through arrays of hot cylinders.The thus validated compressible LB-FD-PF hybrid scheme is used to study the dependence of heat transfer on flow and thermal boundary conditions(Reynolds number,temperature difference between the hot solid bodies and the inlet gas),porosity as well as on the shape of solid objects.Results are rationalized in terms of the residence time of the gas close to the solid body and downstream variations of gas velocity and temperature.Perspective for further applications of the proposed methodology are also discussed.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10921062,10902115 and 11172309)
文摘In this paper,characteristics of flow and convective heat transfer of China RP-3 kerosene in straight circular pipe were numerically studied.Navier-Stokes equations were solved using RNG k-turbulence model with low Reynolds number correction.The thermophysical and transport properties of the China RP-3 kerosene were calculated with a 10-species surrogate and the extended corresponding state method(ECS) combined with Benedict-Webb-Rubin equation.The independence of grids was first studied and the numerical results were then compared with experimental data for validation.Under flow conditions given in the paper,the results show that deterioration of convective heat transfer occurs when the wall temperature is slightly higher than the pseudo-critical temperature of kerosene for cases with wall heat flux of 1.2 and 0.8 MW/m 2.The degree of the heat transfer deterioration is weakened as the heat flux decreases.The deterioration,however,does not happen when the heat flux on the pipe wall is reduced to 0.5 MW/m 2.Based on the analysis of the near-wall turbulent properties,it is found that the heat transfer deterioration and then the enhancement are attributed partly to the change in the turbulent kinetic energy in the vicinity of pipe wall.The conventional heat transfer relations such as Sieder-Tate and Gnielinski formulas can be used for the estimation of kerosene heat convection under subcritical conditions,but they are not capable of predicting the phenomenon of heat transfer deterioration.The modified Bae-Kim formula can describe the heat transfer deterioration.In addition,the frictional drag would increase dramatically when the fuel transforms to the supercritical state.
基金supported by the Aeronautical Science Foundation of China(Grant No.2020Z009063001)the Fundamental Research Funds for the Central Universities(Grant No.DUT22GF303)。
文摘Topology optimization of simplified convective heat transfer has been widely studied,but most existing studies are based on the finite element method(FEM);methods based on the finite volume method(FVM)have been less studied.In this paper,a topology optimization method based on FVM was proposed for a simplified convective heat transfer problem.We developed a novel adjoint sensitivity analysis method applicable to FVM,which included adjoint equations,corresponding boundary conditions,and sensitivity analysis equations.Additionally,a program for the proposed topology optimization method was developed in open field operation and manipulation(OpenFOAM)and portable,extensibletoolkit for scientific computation(PETSc).Thus,large-scale topology optimizations could be performed in parallel.Furthermore,numerical examples of the classical two-dimensional(2D)and 3D optimization problems were considered.The results verified the effectiveness and feasibility of the proposed method.The results of large-scale 3D examples show an interesting phenomenon that for the optimized designs with few features,the large-scale topology optimization is still valuable for obtaining more effective structural shapes.
基金support of the Comite Mixte Franco-Tunisien pour la Cooperation Universitaire(Project CMCU N°08G1131)
文摘The present study concerns the measurement of the convective heat transfer coefficient on the solid-fluid interface by the pulsed photothermal method.This non-intrusive technique is apphed for the measurement of the local heat transfer coefficients in cooling of a rectangular slab that simulates an electronic component.The heat transfer coefficient is deduced from the evolution of the transient temperature induced by a sudden deposit of a luminous energy on the front face of the slab.In order to draw up the heat transfer cartography by a non-destructive tool, the infrared thermography has been used.Two inverse techniques for the identification of the heat transfer coefficient are presented here.The first one is based on the assumption that heat transfer coefficient remains constant during the pulsed experiment,and the second one considered it variable in space and time.The temporal and spatial evolutions are expressed as a constant heat transfer coefficient(h_0)multiplied by a function of time and space f(x,t).The function f is deduced from the resolution of the conjugated convection-conduction problem,by a control volume technique for the case of thermally thick sample.The results are given for different air velocities and deflection angles of the flow.
基金supported by Chinese Heilongjiang Postdoctoral FoundationChinese Heilongjiang Postdoctoral Science Funding No.LBH-Q07036+1 种基金the Science Creative Foundation for Distinguished Young Scholars in Harbin (Grant No. 2008RFLG005)Project Supported by Natural Scientific Research Innovation Foundation in Harbin Institute of Technology No.HIT.NSRIF. 2008.43.
文摘This paper is concerned with the forced convective heat transfer of dilute liquid suspensions of nanoparticles (nanofluids) flowing through a straight pipe under laminar conditions. Stable nanofluids are formulated by using the high shear mixing and ultrasonication methods. They are then characterised for their size, surface charge,thermal and rheological properties and tested for their convective heat transfer behaviour. Mathematical modelling is performed to simulate the convective heat transfer of nanofluids using a single phase flow model and considering nanofluids as both Newtonian and non-Newtonian fluid. Both experiments and mathematical modelling show that nanofluids can substantially enhance the convective heat transfer. Analyses of the results suggest that the non-Newtonian character of nanofluids influences the overall enhancement, especially for nanofluids with an obvious non-Newtonian character.
基金supported by the National Basic Research Program of China(Grant No.2013CB228302)
文摘In this study, exergy efficiency is defined to evaluate convective heat transfer in a tube based on the local exergy destruction rate from the equilibrium equation of available potential. By calculating this destruction rate, the local irreversibility of convective heat transfer can be evaluated quantitatively. The exergy efficiency and distribution of local exergy destruction rate for a smooth tube, an enhanced tube into which short-width twisted tape has been inserted, and an optimized tube with exergy destruction minimization are analyzed by solving the governing equations through a finite volume method(FVM). For the smooth tube, the exergy efficiency increases with increasing Reynolds number(Re) and decreases as the heat flux increases, whereas the Nusselt number(Nu) remains constant. For the enhanced tube, the exergy efficiency increases with increasing Reynolds number and increases as the short-width rate(w) increases. An analysis of the distribution of the local exergy destruction rate for a smooth tube shows that exergy destruction in the annular region between the core flow and tube wall is the highest. Furthermore, the exergy destruction for the enhanced and optimized tubes is reduced compared with that of the smooth tube. When the Reynolds number varies from 500 to 1750, the exergy efficiencies for the smooth, enhanced, and optimized tubes are in the ranges 0.367–0.485, 0.705–0.857, and 0.885–0.906, respectively. The results show that exergy efficiency is an effective evaluation criterion for convective heat transfer and the distribution of the local exergy destruction rate reveals the distribution of local irreversible loss. Disturbance in the core flow can reduce exergy destruction, and improve the exergy efficiency as well as heat transfer rate. Besides, optimization with exergy destruction minimization can provide effective guidance to improve the technology of heat transfer enhancement.
基金the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(Grant No.51621062)。
文摘The entransy theory is widely used and found to be effective in thermal analyses and optimizations.Some researchers considered the entransy variation due to viscous heating as part of entransy dissipation and analyzed convective heat transfer based on the differential relationship between entropy and entransy.However,it has been pointed out that the derivation of the differential relationship between entropy and entransy is incorrect.In this paper,the convective heat transfer processes with viscous heating is reconsidered and analyzed from the viewpoint of the energy conservation and the entransy balance equation.It is shown that the influence of the viscous heating is equivalent to that of an inner heat source.Therefore,the contribution of viscous heating to system entransy should not be treated as part of entransy dissipation,but entransy flow into the system.Two-stream parallel and counter flow heat exchangers with viscous heating and a thermal insulation transportation problem of heavy oil are taken as examples to verify the theoretical analyses intuitively.In the examples,the numerical results show that the entransy dissipation rates could be negative when the influence of the viscous heating on the system entransy is treated as part of the entransy dissipation.This is obviously unreasonable.Meanwhile,when the entransy contribution from the viscous heating to the system entransy is treated as entransy flow into the system,it is shown that the entransy dissipation rate is always positive,and the heat transfer processes can be well explained with the entransy theory.
基金supported by the National Natural Science Foundation of China(Grant Nos.51736004,and 52076088)the Foundation of State Key Laboratory of Coal Combustion(Grant No.FSKLCCA2007)。
文摘A significant way to achieve energy saving and emission reduction is to optimize the design of heat transfer devices.As is widely applied in industry,a corrugated tube constructed by B-spline curve is numerically investigated and the profile is optimized,using a surrogate model with considerations of performance evaluation criterion(PEC)as single objective or minimum flow resistance(f)and maximum Nusselt number(Nu)as multi-objective.The machine learning technique is used to determine the candidate samples to update the surrogate model for improving the optimization efficiency and reliability,which is validated to be effective in this paper.The optimization results show that the comprehensive performance of the corrugated tube is more sensitive to the vertical coordinates of the control points,with the appropriate increase in the number of control points for Bspline,and the better performance of corrugated tubes is achieved.The optimal profile corresponding to the best comprehensive performance is a double-crest shape.With Reynolds number(Re)increased,the wave-amplitude of the first wave gradually gets smaller,and the profile of the corrugated tube becomes smoother.With the increasing consideration of heat transfer performance over multi-objective optimization,the optimal shape gradually changes from a double-trough to a single-trough shape.Finally,the maximum PEC of 1.2415,1.1845,and 1.1504 are acquired with the Re=8000,10000,and 12000,respectively,and the maximum Nu increases from 358.540 to 478.821.Compared with the design with the maximum thermal performance,the best compromise solution from multi-objective optimization is determined at Re=8000,10000,and 12000,showing improved flow resistance of 83.917%,85.465%,and 84.473%,but with sacrificed thermal performance of 36.754%,37.088%,and 35.005%,respectively.
文摘A parabolic trough solar collector(PTSC)converts solar radiation into thermal energy.However,low thermal efficiency of PTSC poses a hindrance to the deployment of solar thermal power plants.Thermal performance of PTSC is enhanced in this study by incorporating magnetic nanoparticles into the working fluid.The circular receiver pipe,with dimensions of 66 mm diameter,2 mm thickness,and 24 m length,is exposed to uniform temperature and velocity conditions.The working fluid,Therminol-66,is supplemented with Fe3O4 magnetic nanoparticles at concentrations ranging from 1%to 4%.The findings demonstrate that the inclusion of nanoparticles increases the convective heat transfer coefficient(HTC)of the PTSC,with higher nanoparticle volume fractions leading to greater heat transfer but increased pressure drop.The thermal enhancement factor(TEF)of the PTSC is positively affected by the volume fraction of nanoparticles,both with and without a magnetic field.Notably,the scenario with a 4%nanoparticle volume fraction and a magnetic field strength of 250 G exhibits the highest TEF,indicating superior thermal performance.These findings offer potential avenues for improving the efficiency of PTSCs in solar thermal plants by introducing magnetic nanoparticles into the working fluid.
基金Project supported by the Shahrood University of Technology (No. 17024),Iran
文摘An exact analytical solution is obtained for convective heat transfer in straight ducts with rectangular cross-sections for the first time.This solution is valid for both H1 and H2 boundary conditions,which are related to fully developed convective heat transfer under constant heat flux at the duct walls.The separation of variables method and various other mathematical techniques are used to find the closed form of the temperature distribution.The local and mean Nusselt numbers are also obtained as functions of the aspect ratio.A new physical constraint is presented to solve the Neumann problem in non-dimensional analysis for the H2 boundary conditions.This is one of the major innovations of the current study.The analytical results indicate a singularity occurs at a critical aspect ratio of 2.4912 when calculating the local and mean Nusselt numbers.
文摘Forced convective heat transfer in a plate channel filled with metallic spherical particles was investigated experimentally and numerically. The test section, 58 mm×80mm×5mm in size, was heated by a 0.4 mm thick plate electrical heater. The coolant water now rate ranged from 0.015 to 0.833 kg/s.The local wall temperature distribution was measured along with the inlet and outlet fluid temperatures and pressures. The results illustrate the heat transfer augmentation and increased pressure drop caused by the porous medium. The heat transfer coefficient was increased 5-12 times by the porous media although the hydraulic resistance was increased even more. The Nusselt number and the heat transfer coefficient increased with decreasing particIe diameter, while the pressure drop decreased as the particle diameter increased. It was found that, for the conditions studied (metallic packed bed),the effect of thermal dispersion did not need to be considered in the physical model, as opposed to a non-metallic packed bed, where thermal dispersion is important.
基金the National Natural Science Foundation of China(Grant No.12072103)the Fundamental Research Funds for the Central Universities(Grant No.B200202126)+2 种基金the Natural Science Foundation of Jiangsu Province(Grant No.BK20190073)the State Key Laboratory of Acoustics,Chinese Academy of Sciences(Grant No.SKLA202001)the China Postdoctoral Science Foundation(Grant Nos.2017M6I 1669 and 2018T110430).
文摘Convective heat transfer coefficient is one of the most vital parameters which reveals the thermal efficiency of a pipe flow.To obtain such coefficients for problems with variable pipe wall temperature,numerical iterative methods should be used which could be time-consuming and less accurate.In this paper,thermophysical properties of fluids are assumed to be constant.We define a variable related to the temperature gradient of the pipe wall and study the varying law of the local coefficient.Then,a sample-based scheme is proposed to avoid the calculation of a time-consuming problem in the use of solutions with low computing cost.To verify its accuracy,several problems in normal circle pipes with variable factors,such as the various temperatures of the pipe wall,the different radius of the pipe,and various velocities of fluid flow,are well resolved.Meanwhile,its validity in a convergent pipe is also studied.From the obtained results,the high accuracy and efficiency of the proposed scheme can be confirmed.Therefore,the proposed scheme for determining the convective heat transfer coefficient has great potential in engineering problems.
文摘During the past six years comprehensive research programs have been conducted at the Beijing Polytechnic University to provide a better understanding of heat transfer characteristics of existing and condidate cool- ing techniques for electronic and microelectronic devices.This paper provides a review and summary of the programs with emphasis on direct liquid cooling.Included in this review are the heat transfer investigations related to the following cooling modes:liquid free,mixed and forced convection,liquid jet impingement,flowing liquid film cooling,pool boiling,spray cooling,foreign gas jet impingement in liquid pool,and forced convection air-cooling.
基金This research was financially supported by the Beijing Municipal Natural Science Foundation(No.2212041)National Natural Science Foundation of China(No.51804232).
文摘Convective heat transfer and radiative heat transfer are two essential heat transfer modes in the heating process of steel;it is important to understand the role of them during the heating process clearly.The effects of the convective and radiative heat transfer during the heating process of a cast ingot in a tubular furnace have been studied by the designed natural and forced convection experiments and mathematical simulations.The heating time for the center of the ingot to reach the furnace temperature is decreased with the increase in furnace temperature.According to the experimental and simulation results,a model is proposed regarding the role of radiative and convective heat transfer in the heating process.At low temperature,the convective heat transfer plays a dominant role,while at high temperature,the influence of radiative heat transfer is larger.And a critical temperature exists between them.The forced convective heat transfer can enhance the influence of the convective heat transfer.The critical temperature can be shifted to higher temperatures.