During the analysis of stability heat conduction in the composite tubes, firstly, when the temperature boundary conditions are the random conditions, equations of the mean values and variances of the random thermal fu...During the analysis of stability heat conduction in the composite tubes, firstly, when the temperature boundary conditions are the random conditions, equations of the mean values and variances of the random thermal function are transformed. Secondly, when the heat conduct parameters are the fuzzy numbers and the temperature boundary conditions are the random numbers, interval equations of the heat conduction are presented. Thirdly, by comparison of the interval results, the result in the interval analysis is larger than that in the confidence interval. Moreover the error expecting equation is presented. Finally, with upper （lower） approximation in rough set theory, a new method of the interval analysis to deal with the stability heat conduction is presented.展开更多
Based on thermal-entransy theory, the multi-objective constructal design of quadrilateral heat generation body(HGB) with similar shapes of leaves is studied further. The relationship between the aspect ratio of quadri...Based on thermal-entransy theory, the multi-objective constructal design of quadrilateral heat generation body(HGB) with similar shapes of leaves is studied further. The relationship between the aspect ratio of quadrilateral HGB and average temperature difference based on thermal-entransy dissipation is compared with that between the aspect ratio of quadrilateral HGB and the maximum temperature difference(MTD). The relationship between a composite function, consisting of linear weighting sum of the average temperature difference and MTD, and aspect ratio is obtained, and the optimal aspect ratios under minimum composite function with different weighting coefficients are obtained. Using the NSGA-Ⅱ algorithm, the Pareto frontier containing a series of compromise results of average temperature difference and MTD is obtained, and optimization results are compared using the deviation index. There is no aspect ratio to make both MTD and average temperature difference reach the minimum, and the optimal aspect ratio under the minimum MTD is smaller than that under the minimum average temperature difference. The optimal aspect ratio is obtained by making the composite function reach the minimum, and the optimal aspect ratios obtained by minimizing the composite function with different weighting coefficients are different. Compared with the construct of the initial design, the value of the composite function with optimal construct decreases by 1.9%, and the aspect ratio of the quadrilateral HGB decreases by 9.1%. The average temperature difference with the optimal construct increases by 2.1%, and the MTD with the optimal construct decreases by 5.6%. The deviation index under multi-objective optimization is smaller than that under single-objective optimization, and the obtained construct has better comprehensive thermal conductivity. Compared with TOPSIS and LINMAP decision-making methods, the average temperature difference with composite function optimization increases by 0.55% and 0.62% respectively, but the MTD with composite function optimization decreases by 0.84% and 0.96%.展开更多
The intelligent electronic devices have urgent demands for electromagnetic interference(EMI)shielding films with excellent heat dissipation capability.However,it is challenging to obtain excellent EMI shielding and th...The intelligent electronic devices have urgent demands for electromagnetic interference(EMI)shielding films with excellent heat dissipation capability.However,it is challenging to obtain excellent EMI shielding and thermal conductivity performances simultaneously.Herein,inspired by mille-feuille structure,the multifunctional EMI shielding films developed by a layer-by-layer self-assembly and hot-pressing strategy.The ingenious introduction of silver nanoparticles(AgNPs)with large specific surface area and highly conductive into the network formed by TEMPO-oxidized cellulose nanofibrils(TOCNFs)with large aspect ratio to form the TOCNFs/AgNPs.And the graphene nanoplates(GNPs)with high conductivity loss distributed alternately with TOCNFs/AgNPs to construct mille-feuille structure,which had highly efficient conductive network,complete thermally conduction pathway and rich heterogeneous interfaces.Consequently,the designed films presented high electrical conductivity of 8520 S/cm,superb EMI effectiveness(SE)of 98.05 dB,and excellent thermal conductivity of 18.82 W/(m·K).Furthermore,the films possessed outstanding Joule heating performances with low voltages,including high heating temperature(100℃),fast response time(<20 s),and impressive heating stability and reliability.Thus,such high-performance EMI shielding films with fascinating thermal conductivity and Joule heating performances have substantial application in flexible electronics,electromagnetic waves shielding and thermal management.展开更多
Highly thermal conductivity materials with excellent electromagnetic interference shielding and Joule heating performances are ideal for thermal management in the next generation of communication industry,artificial i...Highly thermal conductivity materials with excellent electromagnetic interference shielding and Joule heating performances are ideal for thermal management in the next generation of communication industry,artificial intelligence and wearable electronics.In this work,silver nanowires(AgNWs)are prepared using silver nitrate as the silver source and ethylene glycol as the solvent and reducing agent,and boron nitride(BN)is performed to prepare BN nanosheets(BNNS)with the help of isopropyl alcohol and ultrasonication-assisted peeling method,which are compounded with aramid nanofibers(ANF)prepared by chemical dissociation,respectively,and the(BNNS/ANF)-(AgNWs/ANF)thermal conductivity and electromagnetic interference shielding composite films with Janus structures are prepared by the"vacuum-assisted filtration and hot-pressing"method.Janus(BNNS/ANF)-(AgNWs/ANF)composite films exhibit"one side insulating,one side conducting"performance,the surface resistivity of the BNNS/ANF surface is 4.7×10^(13) Ω,while the conductivity of the AgNWs/ANF surface is 5,275 S/cm.And Janus(BNNS/ANF)-(AgNWs/ANF)composite film with thickness of 95 pm has a high in-plane thermal conductivity coefficient of 8.12 W/(m·K)and superior electromagnetic interference shielding effectiveness of 70 dB.The obtained composite film also has excellent tensile strength of 122.9 MPa and tensile modulus and 2.7 GPa.It also has good temperature-voltage response characteristics(high Joule heating temperature at low supply voltage(5 V,215.0℃),fast response time(10 s)),excellent electrical stability and reliability(stable and constant real-time relative resistance under up to 300 cycles and 1,500 s of tensile-bending fatigue work tests).展开更多
Based on constructal theory,the constructs of three "volume-point" heat conduction models with three-dimensional cylindrical element and rectangular and triangular elements on microscale and nanoscale are op...Based on constructal theory,the constructs of three "volume-point" heat conduction models with three-dimensional cylindrical element and rectangular and triangular elements on microscale and nanoscale are optimized by taking minimum entransy dissipation rate as optimization objective.The optimal constructs of the three "volume-point" heat conduction models with minimum dimensionless equivalent thermal resistance are obtained.The results show that the optimal constructs of the three-dimensional cylindrical assembly based on the minimizations of dimensionless equivalent thermal resistance and dimensionless maximum thermal resistance are different,which is obviously different from the comparison between those of the corresponding two-dimensional rectangular assembly based on the minimizations of these two objectives.The optimal constructs based on rectangular and triangular elements on microscale and nanoscale when the size effect takes effect are obviously different from those when the size effect does not take effect.Because the thermal current density in the high conductivity channel of the rectangular and triangular second order assemblies are not linear with the length,the optimal constructs of these assemblies based on the minimization of entransy dissipation rate are different from those based on the minimization of maximum temperature difference.The dimensionless equivalent thermal resistance defined based on entransy dissipation rate reflects the average heat transfer performance of the construct.The studies on "volume-point" heat conduction constructal problems at three-dimensional conditions and microscale and nanoscale by taking minimum entransy dissipation rate as optimization objective extend the application range of the entransy dissipation extremum principle.展开更多
By taking equivalent thermal resistance, which reflects the average heat conduc- tion effect and is defined based on entransy dissipation, as optimization objective, the "volume to point" constructal problem...By taking equivalent thermal resistance, which reflects the average heat conduc- tion effect and is defined based on entransy dissipation, as optimization objective, the "volume to point" constructal problem of how to discharge the heat generated in a fixed volume to a heat sink on the border through relatively high conductive link is re-analyzed and re-optimized in this paper. The constructal shape of the control volume with the best average heat conduction effect is deduced. For the elemental area and the first order construct assembly, when the thermal current density in the high conductive link is linear with the length, the optimized shapes of assemble based on the minimization of entransy dissipation are the same as those based on minimization of maximum temperature difference, and the mean tem- perature difference is 2/3 of the maximum temperature difference. For the second and higher order construct assemblies, the thermal current densities in the high conductive link are not linear with the length, and the optimized shapes of assem- ble based on the minimization of entransy dissipation are different from those based on minimization of maximum temperature difference. For the same parame- ters, the constructs based on minimization of entransy dissipation and the con- structs based on minimization of maximum temperature difference are compared, and the results show that the constructs based on entransy dissipation can de- crease the mean temperature difference better than the constructs based on mini- mization of maximum temperature difference. But with the increase of the number of the order, the mean temperature difference does not always decrease, and there exist some fluctuations. Because the idea of entransy describes the heat transfer ability more suitably, all of the heat conduction constructal problems may be re-optimized based on it.展开更多
Based on constructal theory,"disc-to-point" heat conduction is optimized by minimizing the entransy dissipation rate whereby a critical point is determined that distributes the high-conductivity material acc...Based on constructal theory,"disc-to-point" heat conduction is optimized by minimizing the entransy dissipation rate whereby a critical point is determined that distributes the high-conductivity material according to optimized radial or branch patterns.The results show that the critical point is determined by the product of the thermal conductivity ratio of the two materials and the volume fraction of the high-conductivity material allocated to the entire volume.The notion of optimal heat transfer performance can be attributed to the disc based on the entransy dissipation extremum principle.Comparing the results based on EDR minimization (entransy dissipation rate minimization) with those based on MTD minimization (maximum temperature difference minimization),one finds that the performance derived from the two optimization procedures are different.When the product of the thermal conductivity ratio and volume fraction is 30,the critical point of the former procedure is that for which the nondimensional radius of the disc equals 1.75,while that of the latter procedure is that for which this radius of the disc equals 2.18.Comparing heat transfer performances from the two procedures,the mean heat transfer temperature difference is decreased more for the former procedure thereby receiving an improved performance quota.展开更多
Based on constructal theory,the structure of a tapered element and high-conductivity link is optimized by taking the minimization of the entransy dissipation rate as the optimization objective.The results show that th...Based on constructal theory,the structure of a tapered element and high-conductivity link is optimized by taking the minimization of the entransy dissipation rate as the optimization objective.The results show that the mean temperature difference of the heat transfer cannot always decrease when the internal complexity of the control-volume increases.There exists an optimal constructal order leading to the minimum mean temperature difference for heat transfer.The thermal current density in high-conductivity links with variable shapes does not linearly depend on the length.Therefore,the optimized constructs based on the minimization of the entransy dissipation rate are different from those based on the minimization of the maximum temperature difference.Compared with the construct based on the minimization of the maximum temperature difference,the construct based on the minimization of the entransy dissipation rate can reduce the mean temperature difference,and improve the heat transfer performance significantly.Because entransy describes the heat transfer ability more suitably,various constructal problems in heat conduction may be addressed more effectively using this basis.展开更多
The Fourier equation of heat conduction predicts a paradox that the effect of a thermal impulse (e.g. the thermal effect in pulse laser) in an infinite medium; i.e., a thermal impulse is propagated in an infinite velo...The Fourier equation of heat conduction predicts a paradox that the effect of a thermal impulse (e.g. the thermal effect in pulse laser) in an infinite medium; i.e., a thermal impulse is propagated in an infinite velocity. In order to solve the thermal transport paradox, C. W. Ulbrich and M. Chester have proposed the modification heat conduction equation respectively from different macroscopic viewpoint. This paper derived the modification heat conduction equation according to phonon model and quantum mechanics from microscopic viewpoint.展开更多
Electronic transport properties can be influenced by the applied electromagnetic fields in conductive materials. The change of the electron distribution function evoked by outfields obeys the Boltzmann equation. In th...Electronic transport properties can be influenced by the applied electromagnetic fields in conductive materials. The change of the electron distribution function evoked by outfields obeys the Boltzmann equation. In this paper, a general law of heat conduction considering the non-uniform electromagnetic effect is developed from the Boltzmann equation. An analysis of the equation leads to the result that the electric field gradient and the magnetic gradient in the conductive material are responsible for the influences of electromagnetic fields on the heat conduction process. A physical model is established and finite element numerical simulation reveals that heat conduction can be increased or delayed by the different directions of the electric field gradient, and the existence of the magnetic gradient always hinders heat conduction.展开更多
文摘During the analysis of stability heat conduction in the composite tubes, firstly, when the temperature boundary conditions are the random conditions, equations of the mean values and variances of the random thermal function are transformed. Secondly, when the heat conduct parameters are the fuzzy numbers and the temperature boundary conditions are the random numbers, interval equations of the heat conduction are presented. Thirdly, by comparison of the interval results, the result in the interval analysis is larger than that in the confidence interval. Moreover the error expecting equation is presented. Finally, with upper （lower） approximation in rough set theory, a new method of the interval analysis to deal with the stability heat conduction is presented.
基金supported by the National Natural Science Foundation of China(Grant No.52171317)。
文摘Based on thermal-entransy theory, the multi-objective constructal design of quadrilateral heat generation body(HGB) with similar shapes of leaves is studied further. The relationship between the aspect ratio of quadrilateral HGB and average temperature difference based on thermal-entransy dissipation is compared with that between the aspect ratio of quadrilateral HGB and the maximum temperature difference(MTD). The relationship between a composite function, consisting of linear weighting sum of the average temperature difference and MTD, and aspect ratio is obtained, and the optimal aspect ratios under minimum composite function with different weighting coefficients are obtained. Using the NSGA-Ⅱ algorithm, the Pareto frontier containing a series of compromise results of average temperature difference and MTD is obtained, and optimization results are compared using the deviation index. There is no aspect ratio to make both MTD and average temperature difference reach the minimum, and the optimal aspect ratio under the minimum MTD is smaller than that under the minimum average temperature difference. The optimal aspect ratio is obtained by making the composite function reach the minimum, and the optimal aspect ratios obtained by minimizing the composite function with different weighting coefficients are different. Compared with the construct of the initial design, the value of the composite function with optimal construct decreases by 1.9%, and the aspect ratio of the quadrilateral HGB decreases by 9.1%. The average temperature difference with the optimal construct increases by 2.1%, and the MTD with the optimal construct decreases by 5.6%. The deviation index under multi-objective optimization is smaller than that under single-objective optimization, and the obtained construct has better comprehensive thermal conductivity. Compared with TOPSIS and LINMAP decision-making methods, the average temperature difference with composite function optimization increases by 0.55% and 0.62% respectively, but the MTD with composite function optimization decreases by 0.84% and 0.96%.
基金support of the National Natural Science Foundation of China(Nos.31901265,22178208)the Key Technology R&D Program of Longyou County(No.JHXM2019063).
文摘The intelligent electronic devices have urgent demands for electromagnetic interference(EMI)shielding films with excellent heat dissipation capability.However,it is challenging to obtain excellent EMI shielding and thermal conductivity performances simultaneously.Herein,inspired by mille-feuille structure,the multifunctional EMI shielding films developed by a layer-by-layer self-assembly and hot-pressing strategy.The ingenious introduction of silver nanoparticles(AgNPs)with large specific surface area and highly conductive into the network formed by TEMPO-oxidized cellulose nanofibrils(TOCNFs)with large aspect ratio to form the TOCNFs/AgNPs.And the graphene nanoplates(GNPs)with high conductivity loss distributed alternately with TOCNFs/AgNPs to construct mille-feuille structure,which had highly efficient conductive network,complete thermally conduction pathway and rich heterogeneous interfaces.Consequently,the designed films presented high electrical conductivity of 8520 S/cm,superb EMI effectiveness(SE)of 98.05 dB,and excellent thermal conductivity of 18.82 W/(m·K).Furthermore,the films possessed outstanding Joule heating performances with low voltages,including high heating temperature(100℃),fast response time(<20 s),and impressive heating stability and reliability.Thus,such high-performance EMI shielding films with fascinating thermal conductivity and Joule heating performances have substantial application in flexible electronics,electromagnetic waves shielding and thermal management.
基金The authors are grateful for the support and funding from the Guangdong Basic and Applied Basic Research Foundation(No.2019B1515120093)Foundation of National Natural Science Foundation of China(Nos.U21A2093 and 51973173)Technological Base Scientific Research Projects(Highly Thermal conductivity Nonmetal Materials).
文摘Highly thermal conductivity materials with excellent electromagnetic interference shielding and Joule heating performances are ideal for thermal management in the next generation of communication industry,artificial intelligence and wearable electronics.In this work,silver nanowires(AgNWs)are prepared using silver nitrate as the silver source and ethylene glycol as the solvent and reducing agent,and boron nitride(BN)is performed to prepare BN nanosheets(BNNS)with the help of isopropyl alcohol and ultrasonication-assisted peeling method,which are compounded with aramid nanofibers(ANF)prepared by chemical dissociation,respectively,and the(BNNS/ANF)-(AgNWs/ANF)thermal conductivity and electromagnetic interference shielding composite films with Janus structures are prepared by the"vacuum-assisted filtration and hot-pressing"method.Janus(BNNS/ANF)-(AgNWs/ANF)composite films exhibit"one side insulating,one side conducting"performance,the surface resistivity of the BNNS/ANF surface is 4.7×10^(13) Ω,while the conductivity of the AgNWs/ANF surface is 5,275 S/cm.And Janus(BNNS/ANF)-(AgNWs/ANF)composite film with thickness of 95 pm has a high in-plane thermal conductivity coefficient of 8.12 W/(m·K)and superior electromagnetic interference shielding effectiveness of 70 dB.The obtained composite film also has excellent tensile strength of 122.9 MPa and tensile modulus and 2.7 GPa.It also has good temperature-voltage response characteristics(high Joule heating temperature at low supply voltage(5 V,215.0℃),fast response time(10 s)),excellent electrical stability and reliability(stable and constant real-time relative resistance under up to 300 cycles and 1,500 s of tensile-bending fatigue work tests).
基金supported by the National Natural Science Foundation of China (Grant No. 51176203)the Natural Science Foundation of Naval University of Engineering (Grant No. HGDYDJJ10011)the Natural Science Foundation for Youngsters of Naval University of Engineering (Grant No. HGDQNJJ10017)
文摘Based on constructal theory,the constructs of three "volume-point" heat conduction models with three-dimensional cylindrical element and rectangular and triangular elements on microscale and nanoscale are optimized by taking minimum entransy dissipation rate as optimization objective.The optimal constructs of the three "volume-point" heat conduction models with minimum dimensionless equivalent thermal resistance are obtained.The results show that the optimal constructs of the three-dimensional cylindrical assembly based on the minimizations of dimensionless equivalent thermal resistance and dimensionless maximum thermal resistance are different,which is obviously different from the comparison between those of the corresponding two-dimensional rectangular assembly based on the minimizations of these two objectives.The optimal constructs based on rectangular and triangular elements on microscale and nanoscale when the size effect takes effect are obviously different from those when the size effect does not take effect.Because the thermal current density in the high conductivity channel of the rectangular and triangular second order assemblies are not linear with the length,the optimal constructs of these assemblies based on the minimization of entransy dissipation rate are different from those based on the minimization of maximum temperature difference.The dimensionless equivalent thermal resistance defined based on entransy dissipation rate reflects the average heat transfer performance of the construct.The studies on "volume-point" heat conduction constructal problems at three-dimensional conditions and microscale and nanoscale by taking minimum entransy dissipation rate as optimization objective extend the application range of the entransy dissipation extremum principle.
基金Supported by the Program for New Century Excellent Talents in University of Chinathe Foundation for the Author of National Excellent Doctoral Dissertation of China (Grant No. 200136)
文摘By taking equivalent thermal resistance, which reflects the average heat conduc- tion effect and is defined based on entransy dissipation, as optimization objective, the "volume to point" constructal problem of how to discharge the heat generated in a fixed volume to a heat sink on the border through relatively high conductive link is re-analyzed and re-optimized in this paper. The constructal shape of the control volume with the best average heat conduction effect is deduced. For the elemental area and the first order construct assembly, when the thermal current density in the high conductive link is linear with the length, the optimized shapes of assemble based on the minimization of entransy dissipation are the same as those based on minimization of maximum temperature difference, and the mean tem- perature difference is 2/3 of the maximum temperature difference. For the second and higher order construct assemblies, the thermal current densities in the high conductive link are not linear with the length, and the optimized shapes of assem- ble based on the minimization of entransy dissipation are different from those based on minimization of maximum temperature difference. For the same parame- ters, the constructs based on minimization of entransy dissipation and the con- structs based on minimization of maximum temperature difference are compared, and the results show that the constructs based on entransy dissipation can de- crease the mean temperature difference better than the constructs based on mini- mization of maximum temperature difference. But with the increase of the number of the order, the mean temperature difference does not always decrease, and there exist some fluctuations. Because the idea of entransy describes the heat transfer ability more suitably, all of the heat conduction constructal problems may be re-optimized based on it.
基金supported by the National Natural Science Foundation of China (10905093)the Program for New Century Excellent Talents in University of China (NCET-04-1006)the Foundation for the Author of National Excellent Doctoral Dissertation of China (200136)
文摘Based on constructal theory,"disc-to-point" heat conduction is optimized by minimizing the entransy dissipation rate whereby a critical point is determined that distributes the high-conductivity material according to optimized radial or branch patterns.The results show that the critical point is determined by the product of the thermal conductivity ratio of the two materials and the volume fraction of the high-conductivity material allocated to the entire volume.The notion of optimal heat transfer performance can be attributed to the disc based on the entransy dissipation extremum principle.Comparing the results based on EDR minimization (entransy dissipation rate minimization) with those based on MTD minimization (maximum temperature difference minimization),one finds that the performance derived from the two optimization procedures are different.When the product of the thermal conductivity ratio and volume fraction is 30,the critical point of the former procedure is that for which the nondimensional radius of the disc equals 1.75,while that of the latter procedure is that for which this radius of the disc equals 2.18.Comparing heat transfer performances from the two procedures,the mean heat transfer temperature difference is decreased more for the former procedure thereby receiving an improved performance quota.
基金supported by the National Natural Science Foundation of China(10905093)the Program for New Century Excellent Talents in Universities of China(NCET-04-1006)the Foundation for the Author of National Excellent Doctoral Dissertations of China(200136)
文摘Based on constructal theory,the structure of a tapered element and high-conductivity link is optimized by taking the minimization of the entransy dissipation rate as the optimization objective.The results show that the mean temperature difference of the heat transfer cannot always decrease when the internal complexity of the control-volume increases.There exists an optimal constructal order leading to the minimum mean temperature difference for heat transfer.The thermal current density in high-conductivity links with variable shapes does not linearly depend on the length.Therefore,the optimized constructs based on the minimization of the entransy dissipation rate are different from those based on the minimization of the maximum temperature difference.Compared with the construct based on the minimization of the maximum temperature difference,the construct based on the minimization of the entransy dissipation rate can reduce the mean temperature difference,and improve the heat transfer performance significantly.Because entransy describes the heat transfer ability more suitably,various constructal problems in heat conduction may be addressed more effectively using this basis.
基金This work was supported by the National Natural Science Foundation of China (No. 60068001)the Natural Science Foundation of Yunnan Province (No. 2000A0021M)ESF of Yunnan (No. 0111054).
文摘The Fourier equation of heat conduction predicts a paradox that the effect of a thermal impulse (e.g. the thermal effect in pulse laser) in an infinite medium; i.e., a thermal impulse is propagated in an infinite velocity. In order to solve the thermal transport paradox, C. W. Ulbrich and M. Chester have proposed the modification heat conduction equation respectively from different macroscopic viewpoint. This paper derived the modification heat conduction equation according to phonon model and quantum mechanics from microscopic viewpoint.
基金supported by the National Basic Research Program of China (No. 2007CB607506)the National Natural Science Foundation of China (No. 90405005)
文摘Electronic transport properties can be influenced by the applied electromagnetic fields in conductive materials. The change of the electron distribution function evoked by outfields obeys the Boltzmann equation. In this paper, a general law of heat conduction considering the non-uniform electromagnetic effect is developed from the Boltzmann equation. An analysis of the equation leads to the result that the electric field gradient and the magnetic gradient in the conductive material are responsible for the influences of electromagnetic fields on the heat conduction process. A physical model is established and finite element numerical simulation reveals that heat conduction can be increased or delayed by the different directions of the electric field gradient, and the existence of the magnetic gradient always hinders heat conduction.
