Attaining a decarbonized and sustainable energy system,which is the core solution to global energy issues,is accessible through the development of hydrogen energy.Proton-exchange membrane water electrolyzers(PEMWEs)ar...Attaining a decarbonized and sustainable energy system,which is the core solution to global energy issues,is accessible through the development of hydrogen energy.Proton-exchange membrane water electrolyzers(PEMWEs)are promising devices for hydrogen production,given their high efficiency,rapid responsiveness,and compactness.Bipolar plates account for a relatively high percentage of the total cost and weight compared with other components of PEMWEs.Thus,optimization of their design may accelerate the promotion of PEMWEs.This paper reviews the advances in materials and flow-field design for bipolar plates.First,the working conditions of proton-exchange membrane fuel cells(PEMFCs)and PEMWEs are compared,including reaction direction,operating temperature,pressure,input/output,and potential.Then,the current research status of bipolar-plate substrates and surface coatings is summarized,and some typical channel-rib flow fields and porous flow fields are presented.Furthermore,the effects of materials on mass and heat transfer and the possibility of reducing corrosion by improving the flow field structure are explored.Finally,this review discusses the potential directions of the development of bipolar-plate design,including material fabrication,flow-field geometry optimization using threedimensional printing,and surface-coating composition optimization based on computational materials science.展开更多
The three-dimensional numerical investigation of an incompressible flow through rib roughened solar air heater is carried out.A combination of thin transverse and truncated ribs is attached on the absorber plate to st...The three-dimensional numerical investigation of an incompressible flow through rib roughened solar air heater is carried out.A combination of thin transverse and truncated ribs is attached on the absorber plate to study its effect on the heat transfer and friction factor.The parameters in the form of Reynolds number(Re)of 4000-16000,relative roughness pitch(P/e)of 8-18 and relative roughness height(e/Dh)of 0.0366-0.055 is considered for the analysis.The CFD code ANSYS FLUENT is used to solve the governing equations of turbulent flow.The RNG k-εturbulence model is used to solve the transport equations with enhanced wall treatment,keeping the Y+<1.The maximum enhancement ratio of the Nusselt number and friction factor obtained is 1.91 and 3.61 respectively.The detailed investigation on average heat transfer,friction factor and flow structures have been discussed.展开更多
Drying is a complicated physical process which involves simultaneous heat and mass transfer in the removal of solvents inside propellants.Inappropriate drying techniques may result in the formation of a hard skin laye...Drying is a complicated physical process which involves simultaneous heat and mass transfer in the removal of solvents inside propellants.Inappropriate drying techniques may result in the formation of a hard skin layer near the surface to block the free access of most solvent through for long stick propellants with large web thickness,which lead to lower drying efficiency and worse drying quality.This study aims to gain a comprehensive understanding of drying process and clarify the mechanism of the blocked layer near the propellant surface.A new three-dimensional coupled heat and mass transfer(3D-CHMT)model was successfully developed under transient conditions.The drying experiment results show that the 3DCHMT model could be applied to describe the drying process well since the relative error of the content of solvent between simulation and experiment values is only 5.5%.The solvent behavior simulation demonstrates that the mass transfer process can be divided into super-fast(SF)and subsequent minorfast(MF)stages,and the SF stage is vital to the prevention of the blocked layer against the free access for solvent molecules inside propellant grains.The effective solvent diffusion coefficient(Deff)of the propellant surface initially increases from 3.4×10^(-6)to 5.3×10^(-6)m^(2)/s as the temperature increases,and then decreases to 4.1×10^(-8)m^(2)/s at 60-100 min.The value of Deffof surface between 0-1.4 mm has a unique trend of change compared with other regions,and it is much lower than that of the internal at100 min under simulation conditions.Meanwhile,the temperature of the propellant surface increases rapidly at the SF stage(0-100 min)and then very slowly thereafter.Both the evolution of Deffand temperature distribution demonstrate that the blocked layer near the propellant surface has been formed in the time period of approximately 0-100 min and its thickness is about 1.4 mm.To mitigate the formation of blocked layer and improve its drying quality of finial propellant products effectively,it should be initially dried at lower drying temperature(30-40℃)in 0-100 min and then dried at higher drying temperature(50-60℃)to reduce drying time for later drying process in double base gun propellants.The present results can provide theoretical guidance for drying process and optimization of drying parameters for long stick propellants with large web thickness.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
Experiments of saturated water flow and heat transfer were conducted for a meter-scale model of regularly fractured granite.The fractured rock model(height 1502.5 mm,width 904 mm,and thickness 300 mm),embedded with tw...Experiments of saturated water flow and heat transfer were conducted for a meter-scale model of regularly fractured granite.The fractured rock model(height 1502.5 mm,width 904 mm,and thickness 300 mm),embedded with two vertical and two horizontal fractures of pre-set apertures,was constructed using 18 pieces of intact granite.The granite was taken from a site currently being investigated for a high-level nuclear waste repository in China.The experiments involved different heat source temperatures and vertical water fluxes in the embedded fractures either open or filled with sand.A finite difference scheme and computer code for calculation of water flow and heat transfer in regularly fractured rocks was developed,verified against both the experimental data and calculations from the TOUGH2 code,and employed for parametric sensitivity analyses.The experiments revealed that,among other things,the temperature distribution was influenced by water flow in the fractures,especially the water flow in the vertical fracture adjacent to the heat source,and that the heat conduction between the neighboring rock blocks in the model with sand-filled fractures was enhanced by the sand,with larger range of influence of the heat source and longer time for approaching asymptotic steady-state than those of the model with open fractures.The temperatures from the experiments were in general slightly smaller than those from the numerical calculations,probably due to the fact that a certain amount of outward heat transfer at the model perimeter was unavoidable in the experiments.The parametric sensitivity analyses indicated that the temperature distribution was highly sensitive to water flow in the fractures,and the water temperature in the vertical fracture adjacent to the heat source was rather insensitive to water flow in other fractures.展开更多
Corrosion products of structural materials when contained in water usually are in two states:soluble state and colloidal particles with dimeter about 10^-3-10^-1um,Deposits of such corrosion products on tube surfaces ...Corrosion products of structural materials when contained in water usually are in two states:soluble state and colloidal particles with dimeter about 10^-3-10^-1um,Deposits of such corrosion products on tube surfaces under high pressure will jeopardize the operating economy of power plant equipment and even esult in accidents.A numerical study is reported in this paper of the natural convective heat and mass transfer on a vertical heated plate subject to the flrst or mixed kind of boundary conditions for high-pressure water(P=17MPa) containing metal corrosion products with consideration of varialbe thermophysical properties.展开更多
The mechanism of pre roll ploughing for 3D fins on the outside surface of copper tube was studied systematically, and especially the process and conditions of 3D fin formation were analyzed. The right mathematical mod...The mechanism of pre roll ploughing for 3D fins on the outside surface of copper tube was studied systematically, and especially the process and conditions of 3D fin formation were analyzed. The right mathematical model was also established. Based on the volume of fin ploughed out is equal to the volume of the metal extruded up by the extruding face of the tool, the relations between fin height, pre roll ploughing feed and pre roll ploughing depth have been achieved. With the increase of pre roll ploughing depth which must be equal to groove depth, the fin height gradually becomes larger. There are different critical feeds with the various depths of pre roll ploughing. The pre roll ploughing feed is the critical one, the height of fin is largest. And when the feed is above the critical one, the fin height will reduce with the increase of feed. The theoretical analysis basically accords with experimental results.展开更多
A model that incorporates the important phenomena in annular gas-water flow through a Venturi tube has been presented. A series of the experiments were carried out to measure the flow and heat transfer characteristics...A model that incorporates the important phenomena in annular gas-water flow through a Venturi tube has been presented. A series of the experiments were carried out to measure the flow and heat transfer characteristics in cold and hog conditions. The comparison between numerical and experimental results shows good agreement.展开更多
A 3- D free surface flow in open channels based on the Reynolds equations with the k-ε turbulence closure model is presented in this paper. Insted of the 'rigid lid' approximation, the solution of the free su...A 3- D free surface flow in open channels based on the Reynolds equations with the k-ε turbulence closure model is presented in this paper. Insted of the 'rigid lid' approximation, the solution of the free surface equation is implemented in the velocity-pressure iterative procedure on the basis of the conventional SIMPLE method. This model was used to compute the flow in rectangular channels with trenches dredged across the bottom. The velocity, eddy viscosity coefficient, turbulent shear stress, turbulent kinetic energy and elevation of the free surface can be obtained. The computed results are in good agreement with previous experimental data.展开更多
Application of CuO-water nanofluid with size of the nanoparticles of 20 nm and volume concentrations up 2% is numerically investigated in a radiator of Chevrolet Suburban diesel engine under turbulent flow conditions....Application of CuO-water nanofluid with size of the nanoparticles of 20 nm and volume concentrations up 2% is numerically investigated in a radiator of Chevrolet Suburban diesel engine under turbulent flow conditions. The heat transfer relations between airflow and nanofluid coolant have been obtained to evaluate local convective and overall heat transfer coefficients and also pumping power for nanofluid flowing in the radiator with a given heat exchange capacity. In the present study, the effects of the automotive speed and Reynolds number of the nanofluid in the different volume concentrations on the radiator performance are also investigated. The results show that for CuO-water nanofluid at 2% volume concentration circulating through the flat tubes with Renf = 6000 while the automotive speed is 70 km/hr, the overall heat transfer coefficient and pumping power are approximately 10% and 23.8% more than that of base fluid for given conditions, respectively.展开更多
Heat transfer and energy performance of Al_(2)O_(3)/water nanofluid in a 90°bend with circular cross-section are investigated in the range of Reynolds number(Re)from 5000 to 30000,particle volume concentration(Φ...Heat transfer and energy performance of Al_(2)O_(3)/water nanofluid in a 90°bend with circular cross-section are investigated in the range of Reynolds number(Re)from 5000 to 30000,particle volume concentration(Φ)from 0.005%to 4%,Schmidt number(Sc)from 9870 to 296100,Dean number(De)from 6636 to 14847.The momentum and energy equations of nanofluid together with the dynamic equation for nanoparticles are solved numerically with the particle convection,diffusion,coagulation and breakage taken into consideration.Some results are validated by comparing with the available experimental or numerical results.The effect of Re,Φ,Sc and De on the friction factor and heat transfer of Al_(2)O_(3)/water nanofluidis discussed.The results showed that the particle number decreases along the pipeline.Increasing De,Sc leads to a decrease and increase ofΦ,respectively.The mean particle diameter and particle polydispersity increase with increasing Debut with decreasing Sc.The friction factor increases with increasingΦ,Sc De and Pr but with decreasing Sc.The ratio of energy performance evaluation criterion(PEC)for the Al_(2)O_(3)/water nanofluid to the base fluid increases with increasing Re,Φand De,but with decreasing Sc.Finally,the expression of ratio of energy PEC for the nanofluid to the base fluid as a function of Re,Φ,Sc and De is derived.展开更多
This study presents the results of the 3D microstructure,thermal conductivity,and heat flow in cement-based foams and examines their changes with a range of densities.Images were captured using X-ray micro computed to...This study presents the results of the 3D microstructure,thermal conductivity,and heat flow in cement-based foams and examines their changes with a range of densities.Images were captured using X-ray micro computed tomography(micro-CT)imaging technique on cement-based foam samples prepared with densities of 400,600,and 800 kg/m^(3).These images were later simulated and quantified using 3D data visualization and analysis software.Based on the analysis,the pore volume of 11000µm^(3)was determined across the three densities,leading to optimal results.However,distinct pore diameters of 15µm for 800 kg/m^(3),and 20µm for 600 and 400 kg/m^(3)were found to be optimum.Most of the pores were spherical,with only 10%appearing elongated or fractured.In addition,a difference of 15%was observed between the 2D and 3D porosity results.Moreover,a difference of 5%was noticed between the experimentally measured thermal conductivity and the numerically predicted value and this variation was constant across the three cast densities.The 3D model showed that heat flows through the cement paste solids and with an increase in porosity this flow reduces.展开更多
The effects of the periodical turbulence and pressure fluctuation on suction surface heat transfer over airfoils of a row of rotor blades with a certain type have been investigated numerically in this paper.The calcul...The effects of the periodical turbulence and pressure fluctuation on suction surface heat transfer over airfoils of a row of rotor blades with a certain type have been investigated numerically in this paper.The calculation is perfomed using v^(2)-f model with the numerical results of pressure fluctuation and heat transfer performance over 4 sample points being analyzed and compared with existing experimental data.It shows that the static pressure change has significant impact on heat transfer performance of the fore suction surface,especially in the active region of the shock waves formed from the trailing edge of upstream nuzzles.While,for the rear suction surface,the flow turbulence contributes more to the heat transfer change over the surface,due to the reduced pressure oscillation through this region.Phase shifted phenomenon across the surface can be observed for both pressure and heat transfer parameters,which should be a result of turbulence migration and wake passing across the airfoil.展开更多
Great advancement has been made on natural gas hydrates exploration and test production in the northern South China Sea.However,there remains a lot of key questions yet to be resolved,particularly about the mechanisms...Great advancement has been made on natural gas hydrates exploration and test production in the northern South China Sea.However,there remains a lot of key questions yet to be resolved,particularly about the mechanisms and the controls of gas hydrates enrichment.Numerical simulaution would play signficant role in addressing these questions.This study focused on the gas hydrate exploration in the Shenhu Area,Northern South China Sea.Based on the newly obtained borehole and multichannel reflection seismic data,the authors conducted an integrated 3D basin modeling study on gas hydrate.The results indicate that the Shenhu Area has favorable conditions for gas hydrate accumulation,such as temperature,pressure,hydrocarbon source,and tectonic setting.Gas hydrates are most concentrated in the Late Miocene strata,particularly in the structual highs between the Baiyun Sag and the Liwan Sag,and area to the south of it.It also proved the existence of overpressure in the main sag of source rocks,which was subject to compaction disequilibrium and hydrocarbon generation.It also shown that the regional fault activity is not conducive to gas hydrate accumulation due to excess gas seepage.The authors conjecture that fault activity may slightly weaken overpressure for the positive effect of hydrocarbon expulsion and areas lacking regional fault activity have better potential.展开更多
基金the National Natural Science Foundation of China(No.52125102)the National Key Research and Development Program of China(No.2021YFB4000101)Fundamental Research Funds for t he Central Universities(No.FRF-TP-2021-02C2)。
文摘Attaining a decarbonized and sustainable energy system,which is the core solution to global energy issues,is accessible through the development of hydrogen energy.Proton-exchange membrane water electrolyzers(PEMWEs)are promising devices for hydrogen production,given their high efficiency,rapid responsiveness,and compactness.Bipolar plates account for a relatively high percentage of the total cost and weight compared with other components of PEMWEs.Thus,optimization of their design may accelerate the promotion of PEMWEs.This paper reviews the advances in materials and flow-field design for bipolar plates.First,the working conditions of proton-exchange membrane fuel cells(PEMFCs)and PEMWEs are compared,including reaction direction,operating temperature,pressure,input/output,and potential.Then,the current research status of bipolar-plate substrates and surface coatings is summarized,and some typical channel-rib flow fields and porous flow fields are presented.Furthermore,the effects of materials on mass and heat transfer and the possibility of reducing corrosion by improving the flow field structure are explored.Finally,this review discusses the potential directions of the development of bipolar-plate design,including material fabrication,flow-field geometry optimization using threedimensional printing,and surface-coating composition optimization based on computational materials science.
文摘The three-dimensional numerical investigation of an incompressible flow through rib roughened solar air heater is carried out.A combination of thin transverse and truncated ribs is attached on the absorber plate to study its effect on the heat transfer and friction factor.The parameters in the form of Reynolds number(Re)of 4000-16000,relative roughness pitch(P/e)of 8-18 and relative roughness height(e/Dh)of 0.0366-0.055 is considered for the analysis.The CFD code ANSYS FLUENT is used to solve the governing equations of turbulent flow.The RNG k-εturbulence model is used to solve the transport equations with enhanced wall treatment,keeping the Y+<1.The maximum enhancement ratio of the Nusselt number and friction factor obtained is 1.91 and 3.61 respectively.The detailed investigation on average heat transfer,friction factor and flow structures have been discussed.
基金supported by the National Natural Science Foundation of China(Grant No.22075146)。
文摘Drying is a complicated physical process which involves simultaneous heat and mass transfer in the removal of solvents inside propellants.Inappropriate drying techniques may result in the formation of a hard skin layer near the surface to block the free access of most solvent through for long stick propellants with large web thickness,which lead to lower drying efficiency and worse drying quality.This study aims to gain a comprehensive understanding of drying process and clarify the mechanism of the blocked layer near the propellant surface.A new three-dimensional coupled heat and mass transfer(3D-CHMT)model was successfully developed under transient conditions.The drying experiment results show that the 3DCHMT model could be applied to describe the drying process well since the relative error of the content of solvent between simulation and experiment values is only 5.5%.The solvent behavior simulation demonstrates that the mass transfer process can be divided into super-fast(SF)and subsequent minorfast(MF)stages,and the SF stage is vital to the prevention of the blocked layer against the free access for solvent molecules inside propellant grains.The effective solvent diffusion coefficient(Deff)of the propellant surface initially increases from 3.4×10^(-6)to 5.3×10^(-6)m^(2)/s as the temperature increases,and then decreases to 4.1×10^(-8)m^(2)/s at 60-100 min.The value of Deffof surface between 0-1.4 mm has a unique trend of change compared with other regions,and it is much lower than that of the internal at100 min under simulation conditions.Meanwhile,the temperature of the propellant surface increases rapidly at the SF stage(0-100 min)and then very slowly thereafter.Both the evolution of Deffand temperature distribution demonstrate that the blocked layer near the propellant surface has been formed in the time period of approximately 0-100 min and its thickness is about 1.4 mm.To mitigate the formation of blocked layer and improve its drying quality of finial propellant products effectively,it should be initially dried at lower drying temperature(30-40℃)in 0-100 min and then dried at higher drying temperature(50-60℃)to reduce drying time for later drying process in double base gun propellants.The present results can provide theoretical guidance for drying process and optimization of drying parameters for long stick propellants with large web thickness.
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Project (No 50778014) supported by the National Natural Science Foundation of China
文摘Experiments of saturated water flow and heat transfer were conducted for a meter-scale model of regularly fractured granite.The fractured rock model(height 1502.5 mm,width 904 mm,and thickness 300 mm),embedded with two vertical and two horizontal fractures of pre-set apertures,was constructed using 18 pieces of intact granite.The granite was taken from a site currently being investigated for a high-level nuclear waste repository in China.The experiments involved different heat source temperatures and vertical water fluxes in the embedded fractures either open or filled with sand.A finite difference scheme and computer code for calculation of water flow and heat transfer in regularly fractured rocks was developed,verified against both the experimental data and calculations from the TOUGH2 code,and employed for parametric sensitivity analyses.The experiments revealed that,among other things,the temperature distribution was influenced by water flow in the fractures,especially the water flow in the vertical fracture adjacent to the heat source,and that the heat conduction between the neighboring rock blocks in the model with sand-filled fractures was enhanced by the sand,with larger range of influence of the heat source and longer time for approaching asymptotic steady-state than those of the model with open fractures.The temperatures from the experiments were in general slightly smaller than those from the numerical calculations,probably due to the fact that a certain amount of outward heat transfer at the model perimeter was unavoidable in the experiments.The parametric sensitivity analyses indicated that the temperature distribution was highly sensitive to water flow in the fractures,and the water temperature in the vertical fracture adjacent to the heat source was rather insensitive to water flow in other fractures.
文摘Corrosion products of structural materials when contained in water usually are in two states:soluble state and colloidal particles with dimeter about 10^-3-10^-1um,Deposits of such corrosion products on tube surfaces under high pressure will jeopardize the operating economy of power plant equipment and even esult in accidents.A numerical study is reported in this paper of the natural convective heat and mass transfer on a vertical heated plate subject to the flrst or mixed kind of boundary conditions for high-pressure water(P=17MPa) containing metal corrosion products with consideration of varialbe thermophysical properties.
文摘The mechanism of pre roll ploughing for 3D fins on the outside surface of copper tube was studied systematically, and especially the process and conditions of 3D fin formation were analyzed. The right mathematical model was also established. Based on the volume of fin ploughed out is equal to the volume of the metal extruded up by the extruding face of the tool, the relations between fin height, pre roll ploughing feed and pre roll ploughing depth have been achieved. With the increase of pre roll ploughing depth which must be equal to groove depth, the fin height gradually becomes larger. There are different critical feeds with the various depths of pre roll ploughing. The pre roll ploughing feed is the critical one, the height of fin is largest. And when the feed is above the critical one, the fin height will reduce with the increase of feed. The theoretical analysis basically accords with experimental results.
文摘A model that incorporates the important phenomena in annular gas-water flow through a Venturi tube has been presented. A series of the experiments were carried out to measure the flow and heat transfer characteristics in cold and hog conditions. The comparison between numerical and experimental results shows good agreement.
文摘A 3- D free surface flow in open channels based on the Reynolds equations with the k-ε turbulence closure model is presented in this paper. Insted of the 'rigid lid' approximation, the solution of the free surface equation is implemented in the velocity-pressure iterative procedure on the basis of the conventional SIMPLE method. This model was used to compute the flow in rectangular channels with trenches dredged across the bottom. The velocity, eddy viscosity coefficient, turbulent shear stress, turbulent kinetic energy and elevation of the free surface can be obtained. The computed results are in good agreement with previous experimental data.
文摘Application of CuO-water nanofluid with size of the nanoparticles of 20 nm and volume concentrations up 2% is numerically investigated in a radiator of Chevrolet Suburban diesel engine under turbulent flow conditions. The heat transfer relations between airflow and nanofluid coolant have been obtained to evaluate local convective and overall heat transfer coefficients and also pumping power for nanofluid flowing in the radiator with a given heat exchange capacity. In the present study, the effects of the automotive speed and Reynolds number of the nanofluid in the different volume concentrations on the radiator performance are also investigated. The results show that for CuO-water nanofluid at 2% volume concentration circulating through the flat tubes with Renf = 6000 while the automotive speed is 70 km/hr, the overall heat transfer coefficient and pumping power are approximately 10% and 23.8% more than that of base fluid for given conditions, respectively.
基金Projects supported by the National Natural Science Foundation of China(Grant No.91852102).
文摘Heat transfer and energy performance of Al_(2)O_(3)/water nanofluid in a 90°bend with circular cross-section are investigated in the range of Reynolds number(Re)from 5000 to 30000,particle volume concentration(Φ)from 0.005%to 4%,Schmidt number(Sc)from 9870 to 296100,Dean number(De)from 6636 to 14847.The momentum and energy equations of nanofluid together with the dynamic equation for nanoparticles are solved numerically with the particle convection,diffusion,coagulation and breakage taken into consideration.Some results are validated by comparing with the available experimental or numerical results.The effect of Re,Φ,Sc and De on the friction factor and heat transfer of Al_(2)O_(3)/water nanofluidis discussed.The results showed that the particle number decreases along the pipeline.Increasing De,Sc leads to a decrease and increase ofΦ,respectively.The mean particle diameter and particle polydispersity increase with increasing Debut with decreasing Sc.The friction factor increases with increasingΦ,Sc De and Pr but with decreasing Sc.The ratio of energy performance evaluation criterion(PEC)for the Al_(2)O_(3)/water nanofluid to the base fluid increases with increasing Re,Φand De,but with decreasing Sc.Finally,the expression of ratio of energy PEC for the nanofluid to the base fluid as a function of Re,Φ,Sc and De is derived.
文摘This study presents the results of the 3D microstructure,thermal conductivity,and heat flow in cement-based foams and examines their changes with a range of densities.Images were captured using X-ray micro computed tomography(micro-CT)imaging technique on cement-based foam samples prepared with densities of 400,600,and 800 kg/m^(3).These images were later simulated and quantified using 3D data visualization and analysis software.Based on the analysis,the pore volume of 11000µm^(3)was determined across the three densities,leading to optimal results.However,distinct pore diameters of 15µm for 800 kg/m^(3),and 20µm for 600 and 400 kg/m^(3)were found to be optimum.Most of the pores were spherical,with only 10%appearing elongated or fractured.In addition,a difference of 15%was observed between the 2D and 3D porosity results.Moreover,a difference of 5%was noticed between the experimentally measured thermal conductivity and the numerically predicted value and this variation was constant across the three cast densities.The 3D model showed that heat flows through the cement paste solids and with an increase in porosity this flow reduces.
基金The authors gratefully acknow ledge the financial support from China Scholarship Council(CSC)and Siemens Industrial Turbomachinery Ltd.(UK)for Liang Guo's Ph.D.research at the University of Nottingham(RIS 101798).
文摘The effects of the periodical turbulence and pressure fluctuation on suction surface heat transfer over airfoils of a row of rotor blades with a certain type have been investigated numerically in this paper.The calculation is perfomed using v^(2)-f model with the numerical results of pressure fluctuation and heat transfer performance over 4 sample points being analyzed and compared with existing experimental data.It shows that the static pressure change has significant impact on heat transfer performance of the fore suction surface,especially in the active region of the shock waves formed from the trailing edge of upstream nuzzles.While,for the rear suction surface,the flow turbulence contributes more to the heat transfer change over the surface,due to the reduced pressure oscillation through this region.Phase shifted phenomenon across the surface can be observed for both pressure and heat transfer parameters,which should be a result of turbulence migration and wake passing across the airfoil.
基金funded by Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(GML2019ZD0201,GML2019ZD0104)Finance Science and Technology Project of Hainan Province(ZDKJ202019).
文摘Great advancement has been made on natural gas hydrates exploration and test production in the northern South China Sea.However,there remains a lot of key questions yet to be resolved,particularly about the mechanisms and the controls of gas hydrates enrichment.Numerical simulaution would play signficant role in addressing these questions.This study focused on the gas hydrate exploration in the Shenhu Area,Northern South China Sea.Based on the newly obtained borehole and multichannel reflection seismic data,the authors conducted an integrated 3D basin modeling study on gas hydrate.The results indicate that the Shenhu Area has favorable conditions for gas hydrate accumulation,such as temperature,pressure,hydrocarbon source,and tectonic setting.Gas hydrates are most concentrated in the Late Miocene strata,particularly in the structual highs between the Baiyun Sag and the Liwan Sag,and area to the south of it.It also proved the existence of overpressure in the main sag of source rocks,which was subject to compaction disequilibrium and hydrocarbon generation.It also shown that the regional fault activity is not conducive to gas hydrate accumulation due to excess gas seepage.The authors conjecture that fault activity may slightly weaken overpressure for the positive effect of hydrocarbon expulsion and areas lacking regional fault activity have better potential.