The recently proposed interface propagation-based method has shown its advantages in obtaining the thermal conductivity of phase change materials during solid-liquid transition over conventional techniques. However, i...The recently proposed interface propagation-based method has shown its advantages in obtaining the thermal conductivity of phase change materials during solid-liquid transition over conventional techniques. However, in previous investigation, the analysis on the measurement error was qualitative and only focused on the total effects on the measurement without decoupling the influencing factors. This paper discusses the effects of influencing factors on the measurement results for the interface propagation-based method. Numerical simulations were performed to explore the influencing factors, namely model simplification, subcooling and natural convection, along with their impact on the measurement process and corresponding measurement results. The numerical solutions were provided in terms of moving curves of the solid-liquid interface and the predicted values of thermal conductivity. Results indicated that the impact of simplified model was strongly dependent on Stefan number of the melting process. The degree of subcooling would lead to underestimated values for thermal conductivity prediction. The natural convection would intensify the heat transfer rate in the liquid region, thereby overestimating the obtained results of thermal conductivity. Correlations and experimental guidelines are provided. The relative errors are limited in ±1.5%,±3%and ±2% corresponding to the impact of simplified model, subcooling and natural convection, respectively.展开更多
The authors presented a new measuring method of the soil thermal conductivity,the probe method,which is designed and made based on the theory of line heat source. This method is used to measure thermal conductivity of...The authors presented a new measuring method of the soil thermal conductivity,the probe method,which is designed and made based on the theory of line heat source. This method is used to measure thermal conductivity of coarse sand,fine sand and silty clay in different water contents. The results that measured by the probe method are well consistent with those of QTM-D_2. The soil thermal conductivity increases in different levels with the increase of the water content. Compared the soil thermal conductivity measured by the probe method in laboratory with in-situ experiment,it shows that the measuring gap gradually increases with the increase of the depth. The reason is that the in-situ measuring thermal conductivity can reflect the actual situation of the soil mass.展开更多
By placing a sample between a heated and a cooled rod, a thermal conductivity of the sample can be evaluated easily with the assumption of a one-dimensional heat flow. However, a three-dimensional constriction/spreadi...By placing a sample between a heated and a cooled rod, a thermal conductivity of the sample can be evaluated easily with the assumption of a one-dimensional heat flow. However, a three-dimensional constriction/spreading heat flow may occur inside the rods when the sample is a composite having different thermal conductivities. In order to investigate the thermal resistance due to the constriction/spreading heat flow, the three-dimensional numerical analyses were conducted on the heat transfer characteristics of the rods. In the present analyses, a polymer-based composite board having thermal vias was sandwiched between the rods. From the numerical results, it was confirmed that the constriction/spreading resistance of the rods was strongly affected by the thermal conductivity of the rods as well as the number and size of the thermal vias. A simple equation was also proposed to evaluate the constriction/spreading resistance of the rods. Fairly good agreements were obtained between the numerical results and the calculated ones by the simple equation. Moreover, the discussion was also made on an effective thermal conductivity of the composite board evaluated with the heated and the cooled rod.展开更多
Modelling temperature-and composition-dependent thermal conductivity in alloys is challengeable and is seldom studied systematically.In the present work,a new model is developed to describe the temperature and concent...Modelling temperature-and composition-dependent thermal conductivity in alloys is challengeable and is seldom studied systematically.In the present work,a new model is developed to describe the temperature and concentration dependence of thermal conductivity for binary alloys.In this new model,firstly thermal conductivity of pure metals was modelled as the function of temperature for each phase and each magnetic state by the corresponding physically sound model.Secondly,in order to describe the composition and temperature dependence of thermal conductivity for solid phases,the combination of the theories of Nordheim and Mott for electric conductivity of alloys with the Wiedemann-Franz law was performed.Thirdly,the reliability of the new model was verified by presently measured thermal conductivities for pure Co,Ni and Co-Ni alloys at 300,600,900 and 1100 K as well as for binary Al-Zn,Mg-Zn and U-Zr systems using the data taken from the literature.The calculated thermal conductivities can well reproduce the measured ones in one-phase regions of a series of Co-Ni alloys.The thermal conductivity in a two-phase region of the Co-Ni system is reasonably predicted as well.It is demonstrated that the new model can be utilized to evaluate the thermal conductivity over the whole investigated composition and temperature ranges for the first time and is expected to be extended to ternary and multicomponent systems by CALPHAD method,which contributes significantly to the development of computational design of materials.展开更多
基金Project(51606224) supported by the National Natural Science Foundation of China
文摘The recently proposed interface propagation-based method has shown its advantages in obtaining the thermal conductivity of phase change materials during solid-liquid transition over conventional techniques. However, in previous investigation, the analysis on the measurement error was qualitative and only focused on the total effects on the measurement without decoupling the influencing factors. This paper discusses the effects of influencing factors on the measurement results for the interface propagation-based method. Numerical simulations were performed to explore the influencing factors, namely model simplification, subcooling and natural convection, along with their impact on the measurement process and corresponding measurement results. The numerical solutions were provided in terms of moving curves of the solid-liquid interface and the predicted values of thermal conductivity. Results indicated that the impact of simplified model was strongly dependent on Stefan number of the melting process. The degree of subcooling would lead to underestimated values for thermal conductivity prediction. The natural convection would intensify the heat transfer rate in the liquid region, thereby overestimating the obtained results of thermal conductivity. Correlations and experimental guidelines are provided. The relative errors are limited in ±1.5%,±3%and ±2% corresponding to the impact of simplified model, subcooling and natural convection, respectively.
基金Supported by Project of National Natural Science Foundation of China(No.41372239)
文摘The authors presented a new measuring method of the soil thermal conductivity,the probe method,which is designed and made based on the theory of line heat source. This method is used to measure thermal conductivity of coarse sand,fine sand and silty clay in different water contents. The results that measured by the probe method are well consistent with those of QTM-D_2. The soil thermal conductivity increases in different levels with the increase of the water content. Compared the soil thermal conductivity measured by the probe method in laboratory with in-situ experiment,it shows that the measuring gap gradually increases with the increase of the depth. The reason is that the in-situ measuring thermal conductivity can reflect the actual situation of the soil mass.
文摘By placing a sample between a heated and a cooled rod, a thermal conductivity of the sample can be evaluated easily with the assumption of a one-dimensional heat flow. However, a three-dimensional constriction/spreading heat flow may occur inside the rods when the sample is a composite having different thermal conductivities. In order to investigate the thermal resistance due to the constriction/spreading heat flow, the three-dimensional numerical analyses were conducted on the heat transfer characteristics of the rods. In the present analyses, a polymer-based composite board having thermal vias was sandwiched between the rods. From the numerical results, it was confirmed that the constriction/spreading resistance of the rods was strongly affected by the thermal conductivity of the rods as well as the number and size of the thermal vias. A simple equation was also proposed to evaluate the constriction/spreading resistance of the rods. Fairly good agreements were obtained between the numerical results and the calculated ones by the simple equation. Moreover, the discussion was also made on an effective thermal conductivity of the composite board evaluated with the heated and the cooled rod.
基金financial support from National Natural Science Foundation of China(Grant No.51671219)is greatly acknowledgedsupported by nanoGinop ProjectGINOP-2.3.2-15-2016-00027 in the framework of the Szechenyi 2020 programsupported by the European Union。
文摘Modelling temperature-and composition-dependent thermal conductivity in alloys is challengeable and is seldom studied systematically.In the present work,a new model is developed to describe the temperature and concentration dependence of thermal conductivity for binary alloys.In this new model,firstly thermal conductivity of pure metals was modelled as the function of temperature for each phase and each magnetic state by the corresponding physically sound model.Secondly,in order to describe the composition and temperature dependence of thermal conductivity for solid phases,the combination of the theories of Nordheim and Mott for electric conductivity of alloys with the Wiedemann-Franz law was performed.Thirdly,the reliability of the new model was verified by presently measured thermal conductivities for pure Co,Ni and Co-Ni alloys at 300,600,900 and 1100 K as well as for binary Al-Zn,Mg-Zn and U-Zr systems using the data taken from the literature.The calculated thermal conductivities can well reproduce the measured ones in one-phase regions of a series of Co-Ni alloys.The thermal conductivity in a two-phase region of the Co-Ni system is reasonably predicted as well.It is demonstrated that the new model can be utilized to evaluate the thermal conductivity over the whole investigated composition and temperature ranges for the first time and is expected to be extended to ternary and multicomponent systems by CALPHAD method,which contributes significantly to the development of computational design of materials.
