The study of transient heat conduction in multilayered slabs is widely used in various engineering fields. In this paper, the transient heat conduction in multilayered slabs with general boundary conditions and arbitr...The study of transient heat conduction in multilayered slabs is widely used in various engineering fields. In this paper, the transient heat conduction in multilayered slabs with general boundary conditions and arbitrary heat generations is analysed. The boundary conditions are general and include various combinations of Dirichlet, Neumann or Robin boundary conditions at either surface. Moreover, arbitrary heat generations in the slabs are taken into account. The solutions are derived by basic methods, including the superposition method, separation variable method and orthogonal expansion method. The simplified double-layered analytical solution is validated by a numerical method and applied to predicting the temporal and spatial distribution of the temperature inside a landfill. It indicates the ability of the proposed analytical solutions for solving the wide range of applied transient heat conduction problems.展开更多
The thermal conduction behavior of the three-dimensional axisymmetric functionally graded circular plate was studied under thermal loads on its top and bottom surfaces. Material properties were taken to be arbitrary d...The thermal conduction behavior of the three-dimensional axisymmetric functionally graded circular plate was studied under thermal loads on its top and bottom surfaces. Material properties were taken to be arbitrary distribution functions of the thickness. A temperature function that satisfies thermal boundary conditions at the edges and the variable separation method were used to reduce equation governing the steady state heat conduction to an ordinary differential equation （ODE） in the thickness coordinate which was solved analytically. Next, resulting variable coefficients ODE due to arbitrary distribution of material properties along thickness coordinate was also solved by the Peano-Baker series. Some numerical examples were given to demonstrate the accuracy, efficiency of the present model, mad to investigate the influence of different distributions of material properties on the temperature field. The numerical results confirm that the influence of different material distributions, gradient indices and thickness of plate to temperature field in plate can not be ignored.展开更多
To make heat conduction equation embody the essence of physical phenomenon under study, dimensionless factors were introduced and the transient heat conduction equation and its boundary conditions were transformed to ...To make heat conduction equation embody the essence of physical phenomenon under study, dimensionless factors were introduced and the transient heat conduction equation and its boundary conditions were transformed to dimensionless forms. Then, a theoretical solution model of transient heat conduction problem in one-dimensional double-layer composite medium was built utilizing the natural eigenfunction expansion method. In order to verify the validity of the model, the results of the above theoretical solution were compared with those of finite element method. The results by the two methods are in a good agreement. The maximum errors by the two methods appear when τ（τ is nondimensional time） equals 0.1 near the boundaries of ζ =1 （ζ is nondimensional space coordinate） and ζ =4. As τ increases, the error decreases gradually, and when τ =5 the results of both solutions have almost no change with the variation of coordinate 4.展开更多
In this work, laser heat conduction lap welding(LHCLW) of AZ31B magnesium alloy sheet and DP780galvanized steel sheet was carried out by the defocused laser beam. The effects of laser power on the microstructure and m...In this work, laser heat conduction lap welding(LHCLW) of AZ31B magnesium alloy sheet and DP780galvanized steel sheet was carried out by the defocused laser beam. The effects of laser power on the microstructure and mechanical properties of the joint were studied. The pros and cons of the joint were identified and evaluated by measuring the tensile shear strength, microhardness and microstructure observation. The formation mechanism of various phases at the Mg/steel interface was analyzed. The results indicated that the galvanized layer could promote the metallurgical bonding between magnesium alloy and steel by improving the diffusion ability of molten magnesium alloy at the steel interface and reacting with Mg, so as to enhance the strength of the joint. A continuous dense layered eutectic structure(α-Mg+MgZn) was formed at the interface of the joint, while MgZn_(2)and MgZn phase was formed at the weld edge zone and heat affective zone(HAZ), whereas no reaction layer was generated between the uncoated steel and magnesium alloy. A sound joint could be obtained at 2.5 kW, and the corresponding tensile shear strength reached the maximum value of 42.9 N/mm. The strength was slightly reduced at 2.6 kW due to the existence of microcracks in the eutectic reaction layer.展开更多
In this paper, a novel calibration integral equation is derived for resolving double-sided, two-probe inverse heat conduction problem of surface heat flux estimation. In contrast to the conventional inverse heat condu...In this paper, a novel calibration integral equation is derived for resolving double-sided, two-probe inverse heat conduction problem of surface heat flux estimation. In contrast to the conventional inverse heat conduction techniques, this calibration approach does not require explicit input of the probe locations, thermophysical properties of the host material and temperature sensor parameters related to thermal contact resistance, sensor capacitance and conductive lead losses. All those parameters and properties are inherently contained in the calibration framework in terms of Volterra integral equation of the first kind. The Laplace transform technique is applied and the frequency domain manipulations of the heat equation are performed for deriving the calibration integral equation. Due to the ill-posed nature, regularization is required for the inverse heat conduction problem, a future-time method or singular value decomposition (SVD) can be used for stabilizing the ill-posed Volterra integral equation of the first kind.展开更多
Serving as gas diffusion layers(GDLs),the thermal conductivity of carbon paper(CP)plays a significant role in the heat transfer management in fuel cells.In the present study,the effect of graphitization degree of CP o...Serving as gas diffusion layers(GDLs),the thermal conductivity of carbon paper(CP)plays a significant role in the heat transfer management in fuel cells.In the present study,the effect of graphitization degree of CP on its through plane thermal conductivity and in-plane thermal conductivity is investigated.The relationship between heat treatment temperatures(1800,2000,2200,2400 and 2500℃)and graphitization degree is also investigated by SEM,XRD and Raman measurements.A model for CP under different graphitization degree is suggested considering the thermal conductivity difference of carbon fiber and matrix carbon.The experimental and simulation results are compared.The results show that the graphitization degree has a significant impact on the through-plane thermal conductivity and in plane thermal conductivity.展开更多
This research was conducted to study the performances of the heat and multilayer reflection insulators used for buildings in South Korea to realize eco-friendly, low-energy-consumption, green construction, and to cont...This research was conducted to study the performances of the heat and multilayer reflection insulators used for buildings in South Korea to realize eco-friendly, low-energy-consumption, green construction, and to contribute to energy consumption reduction in buildings and to the nation＇s greenhouse gas emission reduction policy （targeting 30% reduction compared to BAUCousiness as usual） by 2020）. The heat insulation performance test is about the temperatures on surfaces of test piece. The high air temperature and the low air temperature were measured to determine the overall heat transfer coefficient and thermal conductivity. The conclusions are drawn that the heat transmission coefficients for each type of existing reflection insulator are： A-1 （0.045 W/（m-K））, A-2 （0.031 W/（m.K））, A-3 （0.042 W/（m.K））, A-4 （0.078 W/（m.K））, and the average heat conductivity is 0.049 W/（m-K）; The heat conductivity for each type of Styrofoam insulator are 0.030 W/（m.K） for B-l, 0.032 W/（m-K） for B-2, 0.037 W/（m＇K） for B-3, 0.037 W/（m.K） for B-4, and the average heat conductivity is 0.035 W/（m＇K） regardless of the thickness of the insulator; The heat conductivity values of the multilayer reflection insulators are converted based on the thickness and type C-1 （0.020 W/（m.K））, C-2 （0.018 W/（m.K））, C-3 （0.016 W/（m.K））, and C-4 （0.012 W/（m.K））; The multilayer reflection insulator keeps the indoor-side surface temperature high （during winter） or low （in summer）, enhances the comfort of the building occupants, and conducts heating and moisture resistance to prevent dew condensation on the glass-outer-wall surface.展开更多
The advent of the 5G era has stimulated the rapid development of high power electronics with dense integration.Three-dimensional(3D)thermally conductive networks,possessing high thermal and electrical conductivities a...The advent of the 5G era has stimulated the rapid development of high power electronics with dense integration.Three-dimensional(3D)thermally conductive networks,possessing high thermal and electrical conductivities and many different structures,are regarded as key materials to improve the performance of electronic devices.We provide a critical overview of carbonbased 3D thermally conductive networks,emphasizing their preparation-structure-property relationships and their applications in different scenarios.A detailed discussion of the microscopic principles of thermal conductivity is provided,which is crucial for increasing it.This is followed by an in-depth account of the construction of 3D networks using different carbon materials,such as graphene,carbon foam,and carbon nanotubes.Techniques for the assembly of two-dimensional graphene into 3D networks and their effects on thermal conductivity are emphasized.Finally,the existing challenges and future prospects for 3D carbon-based thermally conductive networks are discussed.展开更多
Effects of heat and mass transfer in the flow of Burgers fluid over an inclined sheet are discussed. Problems formulation and relevant analysis are given in the presence of thermal radiation and non-uniform heat sourc...Effects of heat and mass transfer in the flow of Burgers fluid over an inclined sheet are discussed. Problems formulation and relevant analysis are given in the presence of thermal radiation and non-uniform heat source/sink. Thermal conductivity is taken temperature dependent. The nonlinear partial differential equations are simplified using boundary layer approximations. The resultant nonlinear ordinary differential equations are solved for the series solutions. The convergence of series solutions is obtained by plotting theη-curves for the velocity, temperature and concentration fields. Results of this work describe the role of different physical parameters involved in the problem. The Deborah numbers corresponding to relaxation time(β1 and β2) and angle of inclination(α) decrease the fluid velocity and concentration field. Concentration field decays as Deborah numbers corresponding to retardation time(β3) and mixed convection parameter(G) increase. Large values of heat generation/absorption parameters A/B, and the temperature distribution across the boundary layer increase. Numerical values of local Nusselt number,-θ′(0), and local Sherwood number,-f′(0), are computed and analyzed. It is found that θ′(0) increases with an increase in β3.展开更多
Thermal performance was the most important factor in the development of borehole heat exchanger utilizing geothermal energy. The thermal performance was affected by many different design parameters, such as configurat...Thermal performance was the most important factor in the development of borehole heat exchanger utilizing geothermal energy. The thermal performance was affected by many different design parameters, such as configuration type and borehole size of geothermal heat exchanger. These eventually determined the operation and cost efficiency of the geothermal heat exchanger system. The main purpose of this work was to assess the thermal performance of geother^nal heat exchanger with variation of borehole sizes and numbers of U-tubes inside a borehole. For this, a thermal response test rig was established with line-source theory. The thermal response test was performed with in-line variable input heat source. Effective thermal conductivity and thermal resistance were obtained from the measured data. From the measurement, the effective thermal conductivity is found to have similar values for two- pair type （4 U-tubes） and three-pair type （6 U-tubes） borehole heat exchanger systems indicating similar heat transfer ability. Meanwhile, the thermal resistance shows lower value for the three-pair type compared to the two-pair type. Measured data based resistance have lower value compared to computed result from design programs. Overall comparison finds better thermal performance for the three-pair type, however, fluctuating temperature variation indicates complex flow behavior inside the borehole and requires further study on flow characteristics.展开更多
Carbon fiber reinforced polyamide 12(CF/PA12),a new material renowned for its excellent mechanical and thermal properties,has drawn significant industry attention.Using the steady-state research to heat transfer,a ser...Carbon fiber reinforced polyamide 12(CF/PA12),a new material renowned for its excellent mechanical and thermal properties,has drawn significant industry attention.Using the steady-state research to heat transfer,a series of simulations to investigate the heat transfer properties of CF/PA12 were conducted in this study.Firstly,by building two-and three-dimensional models,the effects of the porosity,carbon fiber content,and arrangement on the heat transfer of CF/PA12 were examined.A validation of the simulation model was carried out and the findings were consistent with those of the experiment.Then,the simulation results using the above models showed that within the volume fraction from 0% to 28%,the thermal conductivity of CF/PA12 increased greatly from 0.0242 W/(m·K)to 10.8848 W/(m·K).The increasing porosity had little influence on heat transfer characteristic of CF/PA12.The direction of the carbon fiber arrangement affects the heat transfer impact,and optimal outcomes were achieved when the heat flow direction was parallel to the carbon fiber.This research contributes to improving the production methods and broadening the application scenarios of composite materials.展开更多
The microstructures and mechanical properties of Al-6Zn-2Mg-1.5Cu-0.4Er alloy under different treatment conditions were investigated by transmission electron microscopy （TEM） observation, and tensile properties and ...The microstructures and mechanical properties of Al-6Zn-2Mg-1.5Cu-0.4Er alloy under different treatment conditions were investigated by transmission electron microscopy （TEM） observation, and tensile properties and hardness test, respectively. The relationship between mechanical properties and microstructures of the alloys was discussed. With trace Er addition to A1-Zn-Mg-Cu alloy, Er and Al interact to form Al3Er phase, which is coherent with a（A1） matrix. The results show that Al-Zn-Mg-Cu alloy after retrogression and re-ageing （RRA） heat treatment exhibits higher tensile strength, ductility and conductivity.展开更多
基金Projects(41530637,41877222,41702290)supported by the National Natural Science Foundation of China
文摘The study of transient heat conduction in multilayered slabs is widely used in various engineering fields. In this paper, the transient heat conduction in multilayered slabs with general boundary conditions and arbitrary heat generations is analysed. The boundary conditions are general and include various combinations of Dirichlet, Neumann or Robin boundary conditions at either surface. Moreover, arbitrary heat generations in the slabs are taken into account. The solutions are derived by basic methods, including the superposition method, separation variable method and orthogonal expansion method. The simplified double-layered analytical solution is validated by a numerical method and applied to predicting the temporal and spatial distribution of the temperature inside a landfill. It indicates the ability of the proposed analytical solutions for solving the wide range of applied transient heat conduction problems.
基金Project(11102136)supported by the National Natural Science Foundation of ChinaProject(2012ZDK04)supported by the Open Project of Guangxi Key Laboratory of Disaster Prevention and Structural Safety,China
文摘The thermal conduction behavior of the three-dimensional axisymmetric functionally graded circular plate was studied under thermal loads on its top and bottom surfaces. Material properties were taken to be arbitrary distribution functions of the thickness. A temperature function that satisfies thermal boundary conditions at the edges and the variable separation method were used to reduce equation governing the steady state heat conduction to an ordinary differential equation （ODE） in the thickness coordinate which was solved analytically. Next, resulting variable coefficients ODE due to arbitrary distribution of material properties along thickness coordinate was also solved by the Peano-Baker series. Some numerical examples were given to demonstrate the accuracy, efficiency of the present model, mad to investigate the influence of different distributions of material properties on the temperature field. The numerical results confirm that the influence of different material distributions, gradient indices and thickness of plate to temperature field in plate can not be ignored.
基金Projects(50576007,50876016) supported by the National Natural Science Foundation of ChinaProjects(20062180) supported by the National Natural Science Foundation of Liaoning Province,China
文摘To make heat conduction equation embody the essence of physical phenomenon under study, dimensionless factors were introduced and the transient heat conduction equation and its boundary conditions were transformed to dimensionless forms. Then, a theoretical solution model of transient heat conduction problem in one-dimensional double-layer composite medium was built utilizing the natural eigenfunction expansion method. In order to verify the validity of the model, the results of the above theoretical solution were compared with those of finite element method. The results by the two methods are in a good agreement. The maximum errors by the two methods appear when τ（τ is nondimensional time） equals 0.1 near the boundaries of ζ =1 （ζ is nondimensional space coordinate） and ζ =4. As τ increases, the error decreases gradually, and when τ =5 the results of both solutions have almost no change with the variation of coordinate 4.
基金Projects(51705219, 51905227) supported by the National Natural Science Foundation of ChinaProject(BK20200915) supported by the Natural Science Foundation of Jiangsu Province,ChinaProject(19KJB460013) supported by the General University Science Research Project of Jiangsu Province,China。
文摘In this work, laser heat conduction lap welding(LHCLW) of AZ31B magnesium alloy sheet and DP780galvanized steel sheet was carried out by the defocused laser beam. The effects of laser power on the microstructure and mechanical properties of the joint were studied. The pros and cons of the joint were identified and evaluated by measuring the tensile shear strength, microhardness and microstructure observation. The formation mechanism of various phases at the Mg/steel interface was analyzed. The results indicated that the galvanized layer could promote the metallurgical bonding between magnesium alloy and steel by improving the diffusion ability of molten magnesium alloy at the steel interface and reacting with Mg, so as to enhance the strength of the joint. A continuous dense layered eutectic structure(α-Mg+MgZn) was formed at the interface of the joint, while MgZn_(2)and MgZn phase was formed at the weld edge zone and heat affective zone(HAZ), whereas no reaction layer was generated between the uncoated steel and magnesium alloy. A sound joint could be obtained at 2.5 kW, and the corresponding tensile shear strength reached the maximum value of 42.9 N/mm. The strength was slightly reduced at 2.6 kW due to the existence of microcracks in the eutectic reaction layer.
文摘In this paper, a novel calibration integral equation is derived for resolving double-sided, two-probe inverse heat conduction problem of surface heat flux estimation. In contrast to the conventional inverse heat conduction techniques, this calibration approach does not require explicit input of the probe locations, thermophysical properties of the host material and temperature sensor parameters related to thermal contact resistance, sensor capacitance and conductive lead losses. All those parameters and properties are inherently contained in the calibration framework in terms of Volterra integral equation of the first kind. The Laplace transform technique is applied and the frequency domain manipulations of the heat equation are performed for deriving the calibration integral equation. Due to the ill-posed nature, regularization is required for the inverse heat conduction problem, a future-time method or singular value decomposition (SVD) can be used for stabilizing the ill-posed Volterra integral equation of the first kind.
基金Projects(2020 JJ 5142,2019 RS 2067)supported by the Science and Technology Planning Project of Hunan Province,ChinaProject(19 C 0581)supported by the Research Foundation of Education Bureau of Hunan Province,China。
文摘Serving as gas diffusion layers(GDLs),the thermal conductivity of carbon paper(CP)plays a significant role in the heat transfer management in fuel cells.In the present study,the effect of graphitization degree of CP on its through plane thermal conductivity and in-plane thermal conductivity is investigated.The relationship between heat treatment temperatures(1800,2000,2200,2400 and 2500℃)and graphitization degree is also investigated by SEM,XRD and Raman measurements.A model for CP under different graphitization degree is suggested considering the thermal conductivity difference of carbon fiber and matrix carbon.The experimental and simulation results are compared.The results show that the graphitization degree has a significant impact on the through-plane thermal conductivity and in plane thermal conductivity.
基金Project(NRF-2010-0024155) supported by the National Research Foundation of Korea
文摘This research was conducted to study the performances of the heat and multilayer reflection insulators used for buildings in South Korea to realize eco-friendly, low-energy-consumption, green construction, and to contribute to energy consumption reduction in buildings and to the nation＇s greenhouse gas emission reduction policy （targeting 30% reduction compared to BAUCousiness as usual） by 2020）. The heat insulation performance test is about the temperatures on surfaces of test piece. The high air temperature and the low air temperature were measured to determine the overall heat transfer coefficient and thermal conductivity. The conclusions are drawn that the heat transmission coefficients for each type of existing reflection insulator are： A-1 （0.045 W/（m-K））, A-2 （0.031 W/（m.K））, A-3 （0.042 W/（m.K））, A-4 （0.078 W/（m.K））, and the average heat conductivity is 0.049 W/（m-K）; The heat conductivity for each type of Styrofoam insulator are 0.030 W/（m.K） for B-l, 0.032 W/（m-K） for B-2, 0.037 W/（m＇K） for B-3, 0.037 W/（m.K） for B-4, and the average heat conductivity is 0.035 W/（m＇K） regardless of the thickness of the insulator; The heat conductivity values of the multilayer reflection insulators are converted based on the thickness and type C-1 （0.020 W/（m.K））, C-2 （0.018 W/（m.K））, C-3 （0.016 W/（m.K））, and C-4 （0.012 W/（m.K））; The multilayer reflection insulator keeps the indoor-side surface temperature high （during winter） or low （in summer）, enhances the comfort of the building occupants, and conducts heating and moisture resistance to prevent dew condensation on the glass-outer-wall surface.
文摘The advent of the 5G era has stimulated the rapid development of high power electronics with dense integration.Three-dimensional(3D)thermally conductive networks,possessing high thermal and electrical conductivities and many different structures,are regarded as key materials to improve the performance of electronic devices.We provide a critical overview of carbonbased 3D thermally conductive networks,emphasizing their preparation-structure-property relationships and their applications in different scenarios.A detailed discussion of the microscopic principles of thermal conductivity is provided,which is crucial for increasing it.This is followed by an in-depth account of the construction of 3D networks using different carbon materials,such as graphene,carbon foam,and carbon nanotubes.Techniques for the assembly of two-dimensional graphene into 3D networks and their effects on thermal conductivity are emphasized.Finally,the existing challenges and future prospects for 3D carbon-based thermally conductive networks are discussed.
文摘Effects of heat and mass transfer in the flow of Burgers fluid over an inclined sheet are discussed. Problems formulation and relevant analysis are given in the presence of thermal radiation and non-uniform heat source/sink. Thermal conductivity is taken temperature dependent. The nonlinear partial differential equations are simplified using boundary layer approximations. The resultant nonlinear ordinary differential equations are solved for the series solutions. The convergence of series solutions is obtained by plotting theη-curves for the velocity, temperature and concentration fields. Results of this work describe the role of different physical parameters involved in the problem. The Deborah numbers corresponding to relaxation time(β1 and β2) and angle of inclination(α) decrease the fluid velocity and concentration field. Concentration field decays as Deborah numbers corresponding to retardation time(β3) and mixed convection parameter(G) increase. Large values of heat generation/absorption parameters A/B, and the temperature distribution across the boundary layer increase. Numerical values of local Nusselt number,-θ′(0), and local Sherwood number,-f′(0), are computed and analyzed. It is found that θ′(0) increases with an increase in β3.
基金Project financially supported by the Second Stage of Brain Korea 21 Projects and Changwon National University,Korea
文摘Thermal performance was the most important factor in the development of borehole heat exchanger utilizing geothermal energy. The thermal performance was affected by many different design parameters, such as configuration type and borehole size of geothermal heat exchanger. These eventually determined the operation and cost efficiency of the geothermal heat exchanger system. The main purpose of this work was to assess the thermal performance of geother^nal heat exchanger with variation of borehole sizes and numbers of U-tubes inside a borehole. For this, a thermal response test rig was established with line-source theory. The thermal response test was performed with in-line variable input heat source. Effective thermal conductivity and thermal resistance were obtained from the measured data. From the measurement, the effective thermal conductivity is found to have similar values for two- pair type （4 U-tubes） and three-pair type （6 U-tubes） borehole heat exchanger systems indicating similar heat transfer ability. Meanwhile, the thermal resistance shows lower value for the three-pair type compared to the two-pair type. Measured data based resistance have lower value compared to computed result from design programs. Overall comparison finds better thermal performance for the three-pair type, however, fluctuating temperature variation indicates complex flow behavior inside the borehole and requires further study on flow characteristics.
基金Projects(52206216,52376085)supported by the National Natural Science Foundation of ChinaProject(2023JJ40744)supported by the Natural Science Foundation of Hunan Province,China。
文摘Carbon fiber reinforced polyamide 12(CF/PA12),a new material renowned for its excellent mechanical and thermal properties,has drawn significant industry attention.Using the steady-state research to heat transfer,a series of simulations to investigate the heat transfer properties of CF/PA12 were conducted in this study.Firstly,by building two-and three-dimensional models,the effects of the porosity,carbon fiber content,and arrangement on the heat transfer of CF/PA12 were examined.A validation of the simulation model was carried out and the findings were consistent with those of the experiment.Then,the simulation results using the above models showed that within the volume fraction from 0% to 28%,the thermal conductivity of CF/PA12 increased greatly from 0.0242 W/(m·K)to 10.8848 W/(m·K).The increasing porosity had little influence on heat transfer characteristic of CF/PA12.The direction of the carbon fiber arrangement affects the heat transfer impact,and optimal outcomes were achieved when the heat flow direction was parallel to the carbon fiber.This research contributes to improving the production methods and broadening the application scenarios of composite materials.
基金Project(2005CB623706) supported by the National Basic Research Program of China
文摘The microstructures and mechanical properties of Al-6Zn-2Mg-1.5Cu-0.4Er alloy under different treatment conditions were investigated by transmission electron microscopy （TEM） observation, and tensile properties and hardness test, respectively. The relationship between mechanical properties and microstructures of the alloys was discussed. With trace Er addition to A1-Zn-Mg-Cu alloy, Er and Al interact to form Al3Er phase, which is coherent with a（A1） matrix. The results show that Al-Zn-Mg-Cu alloy after retrogression and re-ageing （RRA） heat treatment exhibits higher tensile strength, ductility and conductivity.
