The utilization of prefabricated light modular radiant heating system has demonstrated significant increases in heat transfer efficiency and energy conservation capabilities.Within prefabricated building construction,...The utilization of prefabricated light modular radiant heating system has demonstrated significant increases in heat transfer efficiency and energy conservation capabilities.Within prefabricated building construction,this new heating method presents an opportunity for the development of comprehensive facilities.The parameters for evaluating the effectiveness of such a system are the upper surface layer’s heat flux and temperature.In this paper,thermal resistance analysis calculation based on a simplified model for this unique radiant heating system analysis is presented with the heat transfer mechanism’s evaluation.The results obtained from thermal resistance analysis calculation and numerical simulation indicate that the thermal resistance analysis method is highly accurate with temperature discrepancies ranging from 0.44℃ to−0.44℃ and a heat flux discrepancy of less than 7.54%,which can meet the requirements of practical engineering applications,suggesting a foundation for the prefabricated radiant heating system.展开更多
Rapid development of energy,electrical and electronic technologies has put forward higher requirements for the thermal conductivities of polymers and their composites.However,the thermal conductivity coefficient(λ)va...Rapid development of energy,electrical and electronic technologies has put forward higher requirements for the thermal conductivities of polymers and their composites.However,the thermal conductivity coefficient(λ)values of prepared thermally conductive polymer composites are still difficult to achieve expectations,which has become the bottleneck in the fields of thermally conductive polymer composites.Aimed at that,based on the accumulation of the previous research works by related researchers and our research group,this paper proposes three possible directions for breaking through the bottlenecks:(1)preparing and synthesizing intrinsically thermally conductive polymers,(2)reducing the interfacial thermal resistance in thermally conductive polymer composites,and(3)establishing suitable thermal conduction models and studying inner thermal conduction mechanism to guide experimental optimization.Also,the future development trends of the three above-mentioned directions are foreseen,hoping to provide certain basis and guidance for the preparation,researches and development of thermally conductive polymers and their composites.展开更多
Fifteen common rice maintainer lines and 26 high-yielding restorer lines were used to evaluate their thermal resistance and fertility during flowering and early grain filling stages. The rice plants were subjected to ...Fifteen common rice maintainer lines and 26 high-yielding restorer lines were used to evaluate their thermal resistance and fertility during flowering and early grain filling stages. The rice plants were subjected to high temperature stress (39-43 ℃) for 1-15 d from main stem flowering. Based on the heat stress index, they were divided into thermal resistant lines, semi-thermal resistant lines, semi-thermal sensitive lines and thermal sensitive lines. Therefore, the maintainer lines K22B, Bobai B and V20B belonged to thermal resistant lines, whereas 11-32B, Zhongzhe B and Zhong 9B belonged to thermal sensitive lines. For rice restorer lines, Minghui 63 had the highest thermal resistance, followed by R207, P32, P929, and the lowest thermal resistant lines P62-2-2, R8006 and P51. The correlation analysis indicated that the heat stress index was significantly correlated with seed-setting rate and abortive grain rate under heat stress, but not under natural conditions. This indicated that heat stress occurred during flowering and early grain filling stages mainly decreased the seed- setting rate and significantly increased the abortive grain rate in both rice maintainer and restorer lines.展开更多
To predicate the temperature distribution of concrete-filled steel tubes(CFSTs) being exposure to fire,a finite element analysis model was developed using a finite element package,ANSYS.A suggested value of contact th...To predicate the temperature distribution of concrete-filled steel tubes(CFSTs) being exposure to fire,a finite element analysis model was developed using a finite element package,ANSYS.A suggested value of contact thermal resistance was therefore proposed with the supporting of massive numbers of collected test data.Parametric analysis was conducted subsequently towards the cross-sectional temperature distribution of CFST columns in four-side fire,in which the exposure time,width of the cross section,steel ratio were taken into account with considering contact thermal resistance.It was found that contact thermal resistance has little effect on the overall temperature regulation with the exposure time,the width of cross-section or the change of steel ratio.However,great temperature dropping at the concrete adjacent to the contact interface,and gentle temperature increase at steel tube,exist if considering contact thermal resistance.The results of the study are expected to provide theoretical basis for the fire resistance behavior and design of the CFST columns being exposure to fire.展开更多
Au80Sn20 alloy is a widely used solder for laser diode packaging.In this paper,the thermal resistance of Ga N-based blue laser diodes packaged in TO56 cans were measured by the forward voltage method.The microstructur...Au80Sn20 alloy is a widely used solder for laser diode packaging.In this paper,the thermal resistance of Ga N-based blue laser diodes packaged in TO56 cans were measured by the forward voltage method.The microstructures of Au80Sn20 solder were then investigated to understand the reason for the difference in thermal resistance.It was found that the microstructure with a higher content of Au-rich phase in the center of the solder and a lower content of(Au,Ni)Sn phase at the interface of the solder/heat sink resulted in lower thermal resistance.This is attributed to the lower thermal resistance of Au-rich phase and higher thermal resistance of(Au,Ni)Sn phase.展开更多
Using a transient thermoreflectance (TTR) technique, several Au films with different thicknesses on glass and SiC substrates are measured for thermal characterization of metMlic nano-films, including the electron ph...Using a transient thermoreflectance (TTR) technique, several Au films with different thicknesses on glass and SiC substrates are measured for thermal characterization of metMlic nano-films, including the electron phonon coupling factor G, interfazial thermal resistance R, and thermal conductivity Ks of the substrate. The rear heating-front detecting (RF) method is used to ensure the femtosecond temporal resolution. An intense laser beam is focused on the rear surface to heat the film, and another weak laser beam is focused on the very spot of the front surface to detect the change in the electron temperature. By varying the optical path delay between the two beams, a complete electron temperature profile can be scanned. Different from the normally used single-layer model, the double-layer model involving interfaciM thermal resistance is studied here. The electron temperature cooling profile can be affected by the electron energy transfer into the substrate or the electron-phonon interactions in the metallic films. For multiple-target optimization, the genetic algorithm (GA) is used to obtain both G and R. The experimental result gives a deep understanding of the mechanism of ultra-fast heat transfer in metals.展开更多
To improve the thermal conductivity of polymeric composites, the numerous interfacial thermal resistance (ITR) inside is usually considered as a bottle neck, but the direct measurement of the ITR is hardly reported....To improve the thermal conductivity of polymeric composites, the numerous interfacial thermal resistance (ITR) inside is usually considered as a bottle neck, but the direct measurement of the ITR is hardly reported. In this paper, a sandwich structure which consists of transducer/high density polyethylene (HDPE)/sapphire is prepared to study the interface characteristics. Then, the ITRs between HDPE and sapphire of two samples with different HDPE thickness values are measured by time-domain thermoreflectance (TDTR) method and the results are -- 2 × 10-7 m2.K.W-1. Furthermore, a model is used to evaluate the importance of ITR for the thermal conductivity of composites. The model's analysis indicates that reducing the ITR is an effective way of improving the thermal conductivity of composites. These results will provide valuable guidance for the design and manufacture of polymer-based thermally conductive materials.展开更多
In this paper,high-power LED with many integrated chips is used as thermal resistance analysis research object, and we do thermal resistance testing technology research on it. We put forward the thermocouple point con...In this paper,high-power LED with many integrated chips is used as thermal resistance analysis research object, and we do thermal resistance testing technology research on it. We put forward the thermocouple point contact test method. According to the principle that LED forward voltage changes with temperature,LED heat sink to surface temperature distribution is studied directly in the test,and then we analyze the thermal resistance of high-power LED with many integrated chips when its secondary packaging is introduced. This method makes the measurement of thermal resistance of LED more rapid and convenient. It provides an effective assessment method for the analysis of high power LED device design and engineering application.展开更多
The thermal resistance matrix including self-heating thermal resistance and thermal coupling resistance is presented to describe the thermal effects of multi-finger power heterojunction bipolar transistors. The depend...The thermal resistance matrix including self-heating thermal resistance and thermal coupling resistance is presented to describe the thermal effects of multi-finger power heterojunction bipolar transistors. The dependence of thermal resistance matrix on finger spacing is also investigated. It is shown that both self-heating thermal resistance and thermal coupling resistance are lowered by increasing the finger spacing, in which the downward dissipated heat path is widened and the heat flow from adjacent fingers is effectively suppressed. The decrease of self-heating thermal resistance and thermal coupling resistance is helpful for improving the thermal stability of power devices. Furthermore, with the aid of the thermal resistance matrix a 10-finger power heterojunction bipolar transistor (HBT) with non-uniform finger spacing is designed for high thermal stability. The optimized structure can effectively lower the peak temperature while maintaining a uniformity of the temperature profile at various biases and thus the device effectively may operate at a higher power level.展开更多
Using thermal models to describe the heat dissipation process of FCBGA is a significant topic in the field of packaging.However,the thermal resistance model considering the structure of each part of the chip is still ...Using thermal models to describe the heat dissipation process of FCBGA is a significant topic in the field of packaging.However,the thermal resistance model considering the structure of each part of the chip is still ambiguous and rare,but it is quite desirable in engineering.In this work,we propose a detailed thermal resistance network model,and describe it by using thermal conduction resistance and thermal spreading resistance.For a striking FCBGA case,we calculated the thermal resistance of each part of the structure according to the temperature field simulated by COMSOL.The thermal resistance network can be used to predict the temperatures in the chip under different conditions.For example,when the power changes by 40%,the relative error of junction temperature prediction is only 0.24%.The function of the detailed thermal resistance network in evaluating the optimization space and determining the optimization direction is clarified.This work illustrates a potential thermal resistance analysis method for electronic devices such as FCBGA.展开更多
The borehole and total internal thermal resistance are both significant parameters in evaluating the thermal performance of the ground source heat pump.This study aimed to obtain the accurate correlation of the 3D bor...The borehole and total internal thermal resistance are both significant parameters in evaluating the thermal performance of the ground source heat pump.This study aimed to obtain the accurate correlation of the 3D borehole and total internal thermal resistance(R_(b,3D)and R_(a,3D))and analyze the impacts of parameters on the R_(b,3D)and R_(a,3D).Firstly,eight parameters affecting the R_(b,3D)and R_(a,3D),including the borehole diameter,pipe diameter,pipe-pipe distance,borehole depth,soil thermal conductivity,grout thermal conductivity,pipe thermal conductivity,and fluid velocity inside the pipe,were considered and an L-54 design matrix was generated.Then,the 3D numerical model,coupling with the four-resistance model,was proposed to calculate R_(b,3D)and R_(a,3D)for each case.After that,the response surface methodology was employed to obtain and verify the correlation of R_(b,3D)and R_(a,3D),which were compared with the existing resistance calculation methods.Lastly,analysis of variance was carried out to reveal parameters that have statistically significant impacts on the R_(b,3D)and R_(a,3D).Results show that the rationality and accuracy of the correlation of R_(b,3D)and R_(a,3D)can be verified by the determination coefficient and P value of regression model,as well as the P value of lack-of-fit.The existing resistance calculation methods are more or less inaccurate and the discrepancies in some cases can be up to 86.74%and 111.35%for the borehole and total internal thermal resistance.The pipe and grout thermal conductivity,pipe and borehole diameter,and the pipe-pipe distance can be seen as the significant contributory factors to the variation of R_(b,3D)and R_(a,3D).展开更多
Mullite thermal storage ceramics were prepared by low-cost calcined bauxite and kaolin.The phase composition,microstructure,high temperature resistance and thermophysical properties were characterized by modern testin...Mullite thermal storage ceramics were prepared by low-cost calcined bauxite and kaolin.The phase composition,microstructure,high temperature resistance and thermophysical properties were characterized by modern testing techniques.The experimental results indicate that sample A3(bauxite/kaolin ratio of 5:5)sintered at 1620℃has the optimum comprehensive properties,with bulk density of 2.83 g·cm^(-3)and bending strength of 155.44 MPa.After 30 thermal shocks(1000℃-room temperature,air cooling),the bending strength of sample A3 increases to 166.15 MPa with an enhancement rate of 6.89%,the corresponding thermal conductivity and specific heat capacity are 3.54 W·(m·K)^(-1)and 1.39 kJ·(kg·K)^(-1)at 800℃,and the thermal storage density is 1096 kJ·kg^(-1)(25-800 mullite ceramics;sintering properties;high-temperature thermal storage;thermal shock resistance).Mullite forms a dense and continuous interlaced network microstructure,which endows the samples high thermal storage density and high bending strength,but the decrease of bauxite/kaolin ratio leads to the decrease of mullite content,which reduces the properties of the samples.展开更多
The effect of drain-source voltage on A1GaAs/InGaAs PHEMTs thermal resistance is studied by experimental measuring and simulation. The result shows that A1GaAs/InGaAs PHEMTs thermal resistance presents a downward tren...The effect of drain-source voltage on A1GaAs/InGaAs PHEMTs thermal resistance is studied by experimental measuring and simulation. The result shows that A1GaAs/InGaAs PHEMTs thermal resistance presents a downward trend under the same power dissipation when the drain-source voltage (VDs) is decreased. Moreover, the relatively low VDS and large drain-source current (IDs) result in a lower thermal resistance. The chip-level and package-level thermal resistance have been extracted by the structure function method. The simulation result indicated that the high electric field occurs at the gate contact where the temperature rise occurs. A relatively low VDS leads to a relatively low electric field, which leads to the decline of the thermal resistance.展开更多
Methods for the analysis of heat exchangers with various flow arrangements modeling,design,and performance are essential for heat transfer system modeling and its integration with other energy system models.This paper...Methods for the analysis of heat exchangers with various flow arrangements modeling,design,and performance are essential for heat transfer system modeling and its integration with other energy system models.This paper proposes the use of the linear-transfer law for the heat exchanger design and performance analysis as a function of the thermal resistance related to the ratio of a linear temperature difference to the total heat transfer rate.Additionally,we derived a correction factor that represents the influence of the flow arrangement on the heat transfer performance by the effective thermal conductance,as a function of correction factor,heat transfer coefficient,and surface area.Based on the effective thermal conductance,we propose the hot-end NTU and cold-end NTU for deriving a standardized and general thermal resistance formula for different types of heat exchangers by the combination of the correction factor with linear-transfer law.Moreover,for parallel-flow,cross-flow,and 1-2 Tubular Exchanger Manufacturers Association(TEMA)E shell-and-tube heat exchangers,we derived and obtained alternative correction factor expressions without introducing any temperatures.Two cases about heat exchanger design and performance analysis show that the calculation processes using the correction factor-based general thermal resistance are straightforward without any iteration and the calculation results are accurate.Finally,the experimental validation shows that the general thermal resistance formula is appropriate for analyzing the heat transfer performance.That is,the correction factor-based general thermal resistance formula provides a standardized model for heat exchanger analysis and heat transfer/integrated energy system modeling using the heat current method.展开更多
In this study,by using the nonequilibrium molecular dynamics and the kinetic theory,we examine the tailored nanoscale thermal transport via a gas-filled nanogap structure with mechanically-controllable nanopillars in ...In this study,by using the nonequilibrium molecular dynamics and the kinetic theory,we examine the tailored nanoscale thermal transport via a gas-filled nanogap structure with mechanically-controllable nanopillars in one surface only,i.e.,changing nanopillar height.It is found that both the thermal rectification and negative differential thermal resistance(NDTR)effects can be substantially enhanced by controlling the nanopillar height.The maximum thermal rectification ratio can reach 340%and the△T range with NDTR can be significantly enlarged,which can be attributed to the tailored asymmetric thermal resistance via controlled adsorption in height-changing nanopillars,especially at a large temperature difference.These tunable thermal rectification and NDTR mechanisms provide insights for the design of thermal management systems.展开更多
Harsh photothermal temperatures(>50℃)caused heating damage to the normal tissues and induced thermal resistance in cancer cells,which significantly limited the safety and efficacy of photothermal therapy(PTT)in ca...Harsh photothermal temperatures(>50℃)caused heating damage to the normal tissues and induced thermal resistance in cancer cells,which significantly limited the safety and efficacy of photothermal therapy(PTT)in cancer treatment.Mild hyperthermia(<42℃)combined with chemotherapy might solve this issue.Herein,a novel transition metal dichalcogenides nanostructure,namely,Bi_(2)Se_(3)/MoSe_(2)nanosaucers(BMNSs),was designed to produce mild photo-hyperthermia(mPTT)and combined with chemotherapy to improve the overall antitumor efficacy.The BMNSs were constituted by Bi_(2)Se_(3)hexagonal nanoplates and enclosed with MoSe_(2)nanosheets evenly.While the MoSe_(2)moiety endowed the nanoplatform with excellent photothermal efficacy,the Bi_(2)Se_(3)substrates provided large specific surface area to anchor more doxorubicin(DOX)molecules as chemotherapeutic agent.Under the stimuli of mPTT/tumor acidic microenvironment,the tumor-specific drug release and the enhanced chemotherapy could be realized,showing impressive therapeutic outcomes against 4T1 cells.The synergetic therapeutic mechanism might be attributed to the mPTT induced cell membrane permeability,and interestingly,the expression of heat shock proteins 70 was not elevated obviously after the synergetic therapy,thus to avoid the tumor thermal resistance and further improve the therapeutic effect.The in vivo anti-tumoral performance of the BMNSs was further studied and complete tumor eradication was achieved without any recurrence and biotoxicity.Not only demonstrating a paradigm of high therapeutic efficacy of mild hyperthermia and synergistic chemotherapy for precise cancer therapy,our findings proved that the cancer therapeutic effect can be improved with minimal side effects through exquisite designing of the microstructures and the physiochemical properties of the nanoplatform.展开更多
While boron nitride(BN) is widely recognized as the most promising thermally conductive filler for rapidly developing high-power electronic devices due to its excellent thermal conductivity and dielectric properties,a...While boron nitride(BN) is widely recognized as the most promising thermally conductive filler for rapidly developing high-power electronic devices due to its excellent thermal conductivity and dielectric properties,a great challenge is the poor vertical thermal conductivity when embedded in composites owing to the poor interracial interaction causing severe phonon scattering.Here,we report a novel surface modification strategy called the "self-modified nanointerface" using BN nanocrystals(BNNCs) to efficiently link the interface between BN and the polymer matrix.Combining with ice-press assembly method,an only 25 wt% BNembedded composite film can not only possess an in-plane thermal conductivity of 20.3 W m-1K-1but also,more importantly,achieve a through-plane thermal conductivity as high as 21.3 W m-1K-1,which is more than twice the reported maximum due to the ideal phonon spectrum matching between BNNCs and BN fillers,the strong interaction between the self-modified fillers and polymer matrix,as well as ladder-structured BN skeleton.The excellent thermal conductivity has been verified by theoretical calculations and the heat dissipation of a CPU.This study provides an innovative design principle to tailor composite interfaces and opens up a new path to develop high-performance composites.展开更多
A study on heat transfer performance by thermal fluid coupling simulation for the fouling in a shell-tube heat exchanger used in engineering was presented. The coupling simulation was performed in a fluid and solid do...A study on heat transfer performance by thermal fluid coupling simulation for the fouling in a shell-tube heat exchanger used in engineering was presented. The coupling simulation was performed in a fluid and solid domains under three different fouling conditions: fouling inside the tube, fouling outside the tube, and fouling inside the shell. The flow field, temperature, and pressure distributions in the heat exchanger were solved numerically to analyze the heat transfer performance parameters, such as thermal resistance. It is found that the pressure drop of the heat exchanger and the thermal resistance of the tube wall increase by nearly 30% and 20%, respectively, when the relative fouling thickness reaches 10%. The fouling inside the tube has more impact on the heat transfer performance of the heat exchanger, and the fouling inside the shell has less impact.展开更多
Deep submicron partially depleted silicon on insulator(PDSOI) MOSFETs with H-gate were fabricated based on the 0.35μm SOI process developed by the Institute of Microelectronics of the Chinese Academy of Sciences. B...Deep submicron partially depleted silicon on insulator(PDSOI) MOSFETs with H-gate were fabricated based on the 0.35μm SOI process developed by the Institute of Microelectronics of the Chinese Academy of Sciences. Because the self-heating effect(SHE) has a great influence on SOI,extractions of thermal resistance were done for accurate circuit simulation by using the body-source diode as a thermometer.The results show that the thermal resistance in an SOI NMOSFET is lower than that in an SOI PMOSFET;and the thermal resistance in an SOI NMOSFET with a long channel is lower than that with a short channel.This offers a great help to SHE modeling and parameter extraction.展开更多
The study is carried out in imperfect contact with a concrete slab wall attached to a panel based on rice straw compressed in a dynamic frequency regime. We will propose the characterization of thermal insulation for ...The study is carried out in imperfect contact with a concrete slab wall attached to a panel based on rice straw compressed in a dynamic frequency regime. We will propose the characterization of thermal insulation for thermal resistance of contact (<i><span style="font-family:Verdana;">x</span></i><span style="font-family:Verdana;"> = 0.05 m). The impact of heat exchange coefficients on the front face (</span><i><span style="font-family:Verdana;">x</span></i><span style="font-family:Verdana;"> = 0 m) and the rear face (</span><i><span style="font-family:Verdana;">x</span></i><span style="font-family:Verdana;"> = 0.1 m) on these resistors is shown.</span>展开更多
基金Project(NB-2020-JG-07)supported by the Research and Engineering Application of Key Technologies for New Building Industrialization Project of China Northwest Architectural Design and Research Institute Co.,Ltd.Project(2023-CXTD-29)supported by the Key Scientific and Technological Innovation Team of Shaanxi Province,ChinaProject supported by the K.C.Wong Education Foundation。
文摘The utilization of prefabricated light modular radiant heating system has demonstrated significant increases in heat transfer efficiency and energy conservation capabilities.Within prefabricated building construction,this new heating method presents an opportunity for the development of comprehensive facilities.The parameters for evaluating the effectiveness of such a system are the upper surface layer’s heat flux and temperature.In this paper,thermal resistance analysis calculation based on a simplified model for this unique radiant heating system analysis is presented with the heat transfer mechanism’s evaluation.The results obtained from thermal resistance analysis calculation and numerical simulation indicate that the thermal resistance analysis method is highly accurate with temperature discrepancies ranging from 0.44℃ to−0.44℃ and a heat flux discrepancy of less than 7.54%,which can meet the requirements of practical engineering applications,suggesting a foundation for the prefabricated radiant heating system.
基金National Natural Science Foundation of China(51773169 and 51973173)Guangdong Basic and Applied Basic Research Foundation(2019B1515120093)+2 种基金Technological Base Scientific Research ProjectsNatural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province(2019JC-11)Polymer Electromagnetic Functional Materials Innovation Team of Shaanxi Sanqin Scholars.
文摘Rapid development of energy,electrical and electronic technologies has put forward higher requirements for the thermal conductivities of polymers and their composites.However,the thermal conductivity coefficient(λ)values of prepared thermally conductive polymer composites are still difficult to achieve expectations,which has become the bottleneck in the fields of thermally conductive polymer composites.Aimed at that,based on the accumulation of the previous research works by related researchers and our research group,this paper proposes three possible directions for breaking through the bottlenecks:(1)preparing and synthesizing intrinsically thermally conductive polymers,(2)reducing the interfacial thermal resistance in thermally conductive polymer composites,and(3)establishing suitable thermal conduction models and studying inner thermal conduction mechanism to guide experimental optimization.Also,the future development trends of the three above-mentioned directions are foreseen,hoping to provide certain basis and guidance for the preparation,researches and development of thermally conductive polymers and their composites.
基金supported by the National Natural Science Foundation of China(Grant Nos.30871473 and 31101116)the Project from the China National Rice Research Institute(Grant No.2009RG003-5)+1 种基金the Projects from local government of Zhejiang Province, China(Grant Nos.2008C22073,2009C32048 and SN200806)the Zhejiang Provincial Natural Science Foundation,China(Grant Nos.Y3100060 and Y3100090)
文摘Fifteen common rice maintainer lines and 26 high-yielding restorer lines were used to evaluate their thermal resistance and fertility during flowering and early grain filling stages. The rice plants were subjected to high temperature stress (39-43 ℃) for 1-15 d from main stem flowering. Based on the heat stress index, they were divided into thermal resistant lines, semi-thermal resistant lines, semi-thermal sensitive lines and thermal sensitive lines. Therefore, the maintainer lines K22B, Bobai B and V20B belonged to thermal resistant lines, whereas 11-32B, Zhongzhe B and Zhong 9B belonged to thermal sensitive lines. For rice restorer lines, Minghui 63 had the highest thermal resistance, followed by R207, P32, P929, and the lowest thermal resistant lines P62-2-2, R8006 and P51. The correlation analysis indicated that the heat stress index was significantly correlated with seed-setting rate and abortive grain rate under heat stress, but not under natural conditions. This indicated that heat stress occurred during flowering and early grain filling stages mainly decreased the seed- setting rate and significantly increased the abortive grain rate in both rice maintainer and restorer lines.
基金Sponsored by the National Natural Science Foundation of China(Grant No.50708028)the Postdoctoral Foundation of Heilongjiang Province(GrantNo.LBH-Q07048)
文摘To predicate the temperature distribution of concrete-filled steel tubes(CFSTs) being exposure to fire,a finite element analysis model was developed using a finite element package,ANSYS.A suggested value of contact thermal resistance was therefore proposed with the supporting of massive numbers of collected test data.Parametric analysis was conducted subsequently towards the cross-sectional temperature distribution of CFST columns in four-side fire,in which the exposure time,width of the cross section,steel ratio were taken into account with considering contact thermal resistance.It was found that contact thermal resistance has little effect on the overall temperature regulation with the exposure time,the width of cross-section or the change of steel ratio.However,great temperature dropping at the concrete adjacent to the contact interface,and gentle temperature increase at steel tube,exist if considering contact thermal resistance.The results of the study are expected to provide theoretical basis for the fire resistance behavior and design of the CFST columns being exposure to fire.
基金supported by the National Key Research and Development Program of China(Grant Nos.2016YFB0401803,2017YFE0131500,2017YFB0405000)National Natural Science Foundation of China(Grant Nos.61834008,61574160,61804164,and 61704184)+1 种基金Natural Science Foundation of Jiangsu province(BK20180254)China Postdoctoral Science Foundation(2018M630619)。
文摘Au80Sn20 alloy is a widely used solder for laser diode packaging.In this paper,the thermal resistance of Ga N-based blue laser diodes packaged in TO56 cans were measured by the forward voltage method.The microstructures of Au80Sn20 solder were then investigated to understand the reason for the difference in thermal resistance.It was found that the microstructure with a higher content of Au-rich phase in the center of the solder and a lower content of(Au,Ni)Sn phase at the interface of the solder/heat sink resulted in lower thermal resistance.This is attributed to the lower thermal resistance of Au-rich phase and higher thermal resistance of(Au,Ni)Sn phase.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50730006,50976053,and 50906042)
文摘Using a transient thermoreflectance (TTR) technique, several Au films with different thicknesses on glass and SiC substrates are measured for thermal characterization of metMlic nano-films, including the electron phonon coupling factor G, interfazial thermal resistance R, and thermal conductivity Ks of the substrate. The rear heating-front detecting (RF) method is used to ensure the femtosecond temporal resolution. An intense laser beam is focused on the rear surface to heat the film, and another weak laser beam is focused on the very spot of the front surface to detect the change in the electron temperature. By varying the optical path delay between the two beams, a complete electron temperature profile can be scanned. Different from the normally used single-layer model, the double-layer model involving interfaciM thermal resistance is studied here. The electron temperature cooling profile can be affected by the electron energy transfer into the substrate or the electron-phonon interactions in the metallic films. For multiple-target optimization, the genetic algorithm (GA) is used to obtain both G and R. The experimental result gives a deep understanding of the mechanism of ultra-fast heat transfer in metals.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51373184 and 51206167)the National Plan for Science&Technology Support,China(Grant No.2014BAC03B05)the National Basic Research Program of China(Grant Nos.2014CB931803 and 2012CB933801)
文摘To improve the thermal conductivity of polymeric composites, the numerous interfacial thermal resistance (ITR) inside is usually considered as a bottle neck, but the direct measurement of the ITR is hardly reported. In this paper, a sandwich structure which consists of transducer/high density polyethylene (HDPE)/sapphire is prepared to study the interface characteristics. Then, the ITRs between HDPE and sapphire of two samples with different HDPE thickness values are measured by time-domain thermoreflectance (TDTR) method and the results are -- 2 × 10-7 m2.K.W-1. Furthermore, a model is used to evaluate the importance of ITR for the thermal conductivity of composites. The model's analysis indicates that reducing the ITR is an effective way of improving the thermal conductivity of composites. These results will provide valuable guidance for the design and manufacture of polymer-based thermally conductive materials.
基金Sponsored by the Heilongjiang Provincial Project(Grant No.12511121)the Harbin City Innovation Talent Project(Grant No.2011RFXXG019)the National Science and Technology Support Project(Grant No.2012BAH28F02)
文摘In this paper,high-power LED with many integrated chips is used as thermal resistance analysis research object, and we do thermal resistance testing technology research on it. We put forward the thermocouple point contact test method. According to the principle that LED forward voltage changes with temperature,LED heat sink to surface temperature distribution is studied directly in the test,and then we analyze the thermal resistance of high-power LED with many integrated chips when its secondary packaging is introduced. This method makes the measurement of thermal resistance of LED more rapid and convenient. It provides an effective assessment method for the analysis of high power LED device design and engineering application.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61006059, 60776051, and 61006044)the Beijing Municipal Natural Science Foundation of China (Grant No. 4082007)+3 种基金the Beijing Municipal Education Committee of China (Grant Nos. KM200710005015 and KM200910005001)the Beijing Municipal Trans-century Talent Project of China (Grant No. 67002013200301)the Beijing Innovatory Talent Training Program of China (Grant No. 00200054RA001)the Ph. D. Start Science Foundation of Beijing University of Technology of China (Grant No. X0002013201102)
文摘The thermal resistance matrix including self-heating thermal resistance and thermal coupling resistance is presented to describe the thermal effects of multi-finger power heterojunction bipolar transistors. The dependence of thermal resistance matrix on finger spacing is also investigated. It is shown that both self-heating thermal resistance and thermal coupling resistance are lowered by increasing the finger spacing, in which the downward dissipated heat path is widened and the heat flow from adjacent fingers is effectively suppressed. The decrease of self-heating thermal resistance and thermal coupling resistance is helpful for improving the thermal stability of power devices. Furthermore, with the aid of the thermal resistance matrix a 10-finger power heterojunction bipolar transistor (HBT) with non-uniform finger spacing is designed for high thermal stability. The optimized structure can effectively lower the peak temperature while maintaining a uniformity of the temperature profile at various biases and thus the device effectively may operate at a higher power level.
基金supported by the National Natural Science Foundation of China (NSFC) (Grants.52176078, and 51827807)the Research Foundation of Zhongxing Telecom Equipment Corporation (Analysis and optimization of internal thermal resistance of FCBGA chip)the Tsinghua University Initiative Scientific Research Program。
文摘Using thermal models to describe the heat dissipation process of FCBGA is a significant topic in the field of packaging.However,the thermal resistance model considering the structure of each part of the chip is still ambiguous and rare,but it is quite desirable in engineering.In this work,we propose a detailed thermal resistance network model,and describe it by using thermal conduction resistance and thermal spreading resistance.For a striking FCBGA case,we calculated the thermal resistance of each part of the structure according to the temperature field simulated by COMSOL.The thermal resistance network can be used to predict the temperatures in the chip under different conditions.For example,when the power changes by 40%,the relative error of junction temperature prediction is only 0.24%.The function of the detailed thermal resistance network in evaluating the optimization space and determining the optimization direction is clarified.This work illustrates a potential thermal resistance analysis method for electronic devices such as FCBGA.
基金This work was supported by the National Natural Science Foundation of China(No.51708551).
文摘The borehole and total internal thermal resistance are both significant parameters in evaluating the thermal performance of the ground source heat pump.This study aimed to obtain the accurate correlation of the 3D borehole and total internal thermal resistance(R_(b,3D)and R_(a,3D))and analyze the impacts of parameters on the R_(b,3D)and R_(a,3D).Firstly,eight parameters affecting the R_(b,3D)and R_(a,3D),including the borehole diameter,pipe diameter,pipe-pipe distance,borehole depth,soil thermal conductivity,grout thermal conductivity,pipe thermal conductivity,and fluid velocity inside the pipe,were considered and an L-54 design matrix was generated.Then,the 3D numerical model,coupling with the four-resistance model,was proposed to calculate R_(b,3D)and R_(a,3D)for each case.After that,the response surface methodology was employed to obtain and verify the correlation of R_(b,3D)and R_(a,3D),which were compared with the existing resistance calculation methods.Lastly,analysis of variance was carried out to reveal parameters that have statistically significant impacts on the R_(b,3D)and R_(a,3D).Results show that the rationality and accuracy of the correlation of R_(b,3D)and R_(a,3D)can be verified by the determination coefficient and P value of regression model,as well as the P value of lack-of-fit.The existing resistance calculation methods are more or less inaccurate and the discrepancies in some cases can be up to 86.74%and 111.35%for the borehole and total internal thermal resistance.The pipe and grout thermal conductivity,pipe and borehole diameter,and the pipe-pipe distance can be seen as the significant contributory factors to the variation of R_(b,3D)and R_(a,3D).
基金Funded by the National Key Research and Development Program of Science and Technology of China(No.2018YFB1501002)。
文摘Mullite thermal storage ceramics were prepared by low-cost calcined bauxite and kaolin.The phase composition,microstructure,high temperature resistance and thermophysical properties were characterized by modern testing techniques.The experimental results indicate that sample A3(bauxite/kaolin ratio of 5:5)sintered at 1620℃has the optimum comprehensive properties,with bulk density of 2.83 g·cm^(-3)and bending strength of 155.44 MPa.After 30 thermal shocks(1000℃-room temperature,air cooling),the bending strength of sample A3 increases to 166.15 MPa with an enhancement rate of 6.89%,the corresponding thermal conductivity and specific heat capacity are 3.54 W·(m·K)^(-1)and 1.39 kJ·(kg·K)^(-1)at 800℃,and the thermal storage density is 1096 kJ·kg^(-1)(25-800 mullite ceramics;sintering properties;high-temperature thermal storage;thermal shock resistance).Mullite forms a dense and continuous interlaced network microstructure,which endows the samples high thermal storage density and high bending strength,but the decrease of bauxite/kaolin ratio leads to the decrease of mullite content,which reduces the properties of the samples.
基金Project supported by the National Natural Science Foundation of China(Nos.61376077,61201046,61204081)the Beijing Natural Science Foundation(Nos.4132022,4122005)+1 种基金the Guangdong Strategic Emerging Industry Project of China(No.2012A080304003)the Doctoral Fund of Innovation of Beijing University of Technology
文摘The effect of drain-source voltage on A1GaAs/InGaAs PHEMTs thermal resistance is studied by experimental measuring and simulation. The result shows that A1GaAs/InGaAs PHEMTs thermal resistance presents a downward trend under the same power dissipation when the drain-source voltage (VDs) is decreased. Moreover, the relatively low VDS and large drain-source current (IDs) result in a lower thermal resistance. The chip-level and package-level thermal resistance have been extracted by the structure function method. The simulation result indicated that the high electric field occurs at the gate contact where the temperature rise occurs. A relatively low VDS leads to a relatively low electric field, which leads to the decline of the thermal resistance.
基金the National Natural Science Foundation of China(Grant Nos.51806119 and 51836004)the Fundamental Research Funds for the Central Universities(2020MS010)。
文摘Methods for the analysis of heat exchangers with various flow arrangements modeling,design,and performance are essential for heat transfer system modeling and its integration with other energy system models.This paper proposes the use of the linear-transfer law for the heat exchanger design and performance analysis as a function of the thermal resistance related to the ratio of a linear temperature difference to the total heat transfer rate.Additionally,we derived a correction factor that represents the influence of the flow arrangement on the heat transfer performance by the effective thermal conductance,as a function of correction factor,heat transfer coefficient,and surface area.Based on the effective thermal conductance,we propose the hot-end NTU and cold-end NTU for deriving a standardized and general thermal resistance formula for different types of heat exchangers by the combination of the correction factor with linear-transfer law.Moreover,for parallel-flow,cross-flow,and 1-2 Tubular Exchanger Manufacturers Association(TEMA)E shell-and-tube heat exchangers,we derived and obtained alternative correction factor expressions without introducing any temperatures.Two cases about heat exchanger design and performance analysis show that the calculation processes using the correction factor-based general thermal resistance are straightforward without any iteration and the calculation results are accurate.Finally,the experimental validation shows that the general thermal resistance formula is appropriate for analyzing the heat transfer performance.That is,the correction factor-based general thermal resistance formula provides a standardized model for heat exchanger analysis and heat transfer/integrated energy system modeling using the heat current method.
基金the National Natural Science Foundation of China(grants Nos.51976002 and 51776007)Beijing Nova Program of Science and Technology(No.Z191100001119033)the Young Talent Project of Beijing Municipal Education Committee(No.CIT&TCD201904015)。
文摘In this study,by using the nonequilibrium molecular dynamics and the kinetic theory,we examine the tailored nanoscale thermal transport via a gas-filled nanogap structure with mechanically-controllable nanopillars in one surface only,i.e.,changing nanopillar height.It is found that both the thermal rectification and negative differential thermal resistance(NDTR)effects can be substantially enhanced by controlling the nanopillar height.The maximum thermal rectification ratio can reach 340%and the△T range with NDTR can be significantly enlarged,which can be attributed to the tailored asymmetric thermal resistance via controlled adsorption in height-changing nanopillars,especially at a large temperature difference.These tunable thermal rectification and NDTR mechanisms provide insights for the design of thermal management systems.
基金the National Natural Science Foundation of China for the financial support(Nos.51971116,81771981,and 32001005)Shaanxi Provincial Science and Technology Department for financial support(No.2021JM-476)Shaanxi Provincial Administration of Traditional Chinese Medicine for financial support(No.20211-ZZ-JC007).
文摘Harsh photothermal temperatures(>50℃)caused heating damage to the normal tissues and induced thermal resistance in cancer cells,which significantly limited the safety and efficacy of photothermal therapy(PTT)in cancer treatment.Mild hyperthermia(<42℃)combined with chemotherapy might solve this issue.Herein,a novel transition metal dichalcogenides nanostructure,namely,Bi_(2)Se_(3)/MoSe_(2)nanosaucers(BMNSs),was designed to produce mild photo-hyperthermia(mPTT)and combined with chemotherapy to improve the overall antitumor efficacy.The BMNSs were constituted by Bi_(2)Se_(3)hexagonal nanoplates and enclosed with MoSe_(2)nanosheets evenly.While the MoSe_(2)moiety endowed the nanoplatform with excellent photothermal efficacy,the Bi_(2)Se_(3)substrates provided large specific surface area to anchor more doxorubicin(DOX)molecules as chemotherapeutic agent.Under the stimuli of mPTT/tumor acidic microenvironment,the tumor-specific drug release and the enhanced chemotherapy could be realized,showing impressive therapeutic outcomes against 4T1 cells.The synergetic therapeutic mechanism might be attributed to the mPTT induced cell membrane permeability,and interestingly,the expression of heat shock proteins 70 was not elevated obviously after the synergetic therapy,thus to avoid the tumor thermal resistance and further improve the therapeutic effect.The in vivo anti-tumoral performance of the BMNSs was further studied and complete tumor eradication was achieved without any recurrence and biotoxicity.Not only demonstrating a paradigm of high therapeutic efficacy of mild hyperthermia and synergistic chemotherapy for precise cancer therapy,our findings proved that the cancer therapeutic effect can be improved with minimal side effects through exquisite designing of the microstructures and the physiochemical properties of the nanoplatform.
基金the National Natural Science Foundation of China(52173072,51721002 and 52033003)Natural Science Foundation of Shanghai(22ZR1403700).
文摘While boron nitride(BN) is widely recognized as the most promising thermally conductive filler for rapidly developing high-power electronic devices due to its excellent thermal conductivity and dielectric properties,a great challenge is the poor vertical thermal conductivity when embedded in composites owing to the poor interracial interaction causing severe phonon scattering.Here,we report a novel surface modification strategy called the "self-modified nanointerface" using BN nanocrystals(BNNCs) to efficiently link the interface between BN and the polymer matrix.Combining with ice-press assembly method,an only 25 wt% BNembedded composite film can not only possess an in-plane thermal conductivity of 20.3 W m-1K-1but also,more importantly,achieve a through-plane thermal conductivity as high as 21.3 W m-1K-1,which is more than twice the reported maximum due to the ideal phonon spectrum matching between BNNCs and BN fillers,the strong interaction between the self-modified fillers and polymer matrix,as well as ladder-structured BN skeleton.The excellent thermal conductivity has been verified by theoretical calculations and the heat dissipation of a CPU.This study provides an innovative design principle to tailor composite interfaces and opens up a new path to develop high-performance composites.
基金National Natural Science Foundation of China (21878102)
文摘A study on heat transfer performance by thermal fluid coupling simulation for the fouling in a shell-tube heat exchanger used in engineering was presented. The coupling simulation was performed in a fluid and solid domains under three different fouling conditions: fouling inside the tube, fouling outside the tube, and fouling inside the shell. The flow field, temperature, and pressure distributions in the heat exchanger were solved numerically to analyze the heat transfer performance parameters, such as thermal resistance. It is found that the pressure drop of the heat exchanger and the thermal resistance of the tube wall increase by nearly 30% and 20%, respectively, when the relative fouling thickness reaches 10%. The fouling inside the tube has more impact on the heat transfer performance of the heat exchanger, and the fouling inside the shell has less impact.
基金supported by the State Key Development Program for Basic Research of China(No.2006CB3027-01)
文摘Deep submicron partially depleted silicon on insulator(PDSOI) MOSFETs with H-gate were fabricated based on the 0.35μm SOI process developed by the Institute of Microelectronics of the Chinese Academy of Sciences. Because the self-heating effect(SHE) has a great influence on SOI,extractions of thermal resistance were done for accurate circuit simulation by using the body-source diode as a thermometer.The results show that the thermal resistance in an SOI NMOSFET is lower than that in an SOI PMOSFET;and the thermal resistance in an SOI NMOSFET with a long channel is lower than that with a short channel.This offers a great help to SHE modeling and parameter extraction.
文摘The study is carried out in imperfect contact with a concrete slab wall attached to a panel based on rice straw compressed in a dynamic frequency regime. We will propose the characterization of thermal insulation for thermal resistance of contact (<i><span style="font-family:Verdana;">x</span></i><span style="font-family:Verdana;"> = 0.05 m). The impact of heat exchange coefficients on the front face (</span><i><span style="font-family:Verdana;">x</span></i><span style="font-family:Verdana;"> = 0 m) and the rear face (</span><i><span style="font-family:Verdana;">x</span></i><span style="font-family:Verdana;"> = 0.1 m) on these resistors is shown.</span>