This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi...This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi analytical solutions of temperature increment and displacement of multi-layered composite structures are obtained by using the Laplace transform method,upon which the effects of thermal resistance coefficient,partition coefficient,thermal conductivity ratio and heat capacity ratio on the responses are studied.The results show that the generalized imperfect thermal contact model can realistically describe the imperfect thermal contact problem.Accordingly,it may degenerate into other thermal contact models by adjusting the thermal resistance coefficient and partition coefficient.展开更多
The mass transport and ohmic losses in proton exchange membrane fuel cells(PEMFCs)is significantly influenced by the channel to rib width ratio(CRWR),particularly when accounting for the interfacial contact resistance...The mass transport and ohmic losses in proton exchange membrane fuel cells(PEMFCs)is significantly influenced by the channel to rib width ratio(CRWR),particularly when accounting for the interfacial contact resistance between bipolar plates(BPs)and gas diffusion layers(GDLs)(ICRBP-GDL).Both the determination of the optimal CRWR value and the development of an efficient flow field structure are significantly influenced by ICRBP-GDLs.To investigate this,three-dimensional numerical models were developed,revealing that selecting an optimal CRWR tailored to specific ICRBP-GDL values can effectively balance mass transport and ohmic losses.Building on this insight,a novel island two-dimensional flow field design is proposed,demonstrating the ability to enhance oxygen transport to the catalyst layer(CL)and achieve a more uniform oxygen distribution without increasing ohmic losses.Compared to conventional straight and serpentine flow fields,the island flow field improves output power density by 4.5%and 3.5%,respectively,while reducing the liquid water coverage ratio by 30%.Additionally,the study identifies optimal CRWR values for conventional flow fields corresponding to ICRBP-GDLs of 2.5,5,10,20,and 40 mΩ·cm^(2) as 1.5,1.5,1.0,0.67,and 0.43,respectively.For the island flow field,the optimal CRWRs are consistently smaller-1.5,1.0,0.67,0.43,and 0.43-due to its superior mass transfer capability.This work provides a valuable framework for optimizing flow field designs to achieve improved PEMFC performance.展开更多
This paper investigates interfacial heat transfer characteristics in amulti-layer structure under ultra-high heat flux conditions,focusing on thermal contact resistance(TCR)between adjacent layers.Athree-layer computa...This paper investigates interfacial heat transfer characteristics in amulti-layer structure under ultra-high heat flux conditions,focusing on thermal contact resistance(TCR)between adjacent layers.Athree-layer computational model with dual rough interfaces was developed to systematically analyze the synergistic effects of interfacial pressure,surface emissivity,and thermal interface materials(TIMs).Surface reconstruction using experimental measurement data generated two representative roughness models to quantify the impact of surface roughness on heat dissipation.Numerical simulations demonstrate that the absence of TIMs leads to insufficient thermal dissipation capacity under ultra-high heat flux conditions.Compared to TIMapplication,merely increasing the convective heat transfer coefficient shows limited effectiveness in enhancing heat dissipation efficiency.展开更多
In this study,the effects of stacked nanosheets and the surrounding interphase zone on the resistance of the contact region between nanosheets and the tunneling conductivity of samples are evaluated with developed equ...In this study,the effects of stacked nanosheets and the surrounding interphase zone on the resistance of the contact region between nanosheets and the tunneling conductivity of samples are evaluated with developed equations superior to those previously reported.The contact resistance and nanocomposite conductivity are modeled by several influencing factors,including stack properties,interphase depth,tunneling size,and contact diameter.The developed model's accuracy is verified through numerous experimental measurements.To further validate the models and establish correlations between parameters,the effects of all the variables on contact resistance and nanocomposite conductivity are analyzed.Notably,the contact resistance is primarily dependent on the polymer tunnel resistivity,contact area,and tunneling size.The dimensions of the graphene nanosheets significantly influence the conductivity,which ranges from 0 S/m to90 S/m.An increased number of nanosheets in stacks and a larger gap between them enhance the nanocomposite's conductivity.Furthermore,the thicker interphase and smaller tunneling size can lead to higher sample conductivity due to their optimistic effects on the percolation threshold and network efficacy.展开更多
The actively heated fiber-optic(AHFO)technology has become emerged as a research focus due to its advantages of distributed,real-time measurement and good durability.These attributes have led to the gradual applicatio...The actively heated fiber-optic(AHFO)technology has become emerged as a research focus due to its advantages of distributed,real-time measurement and good durability.These attributes have led to the gradual application of AHFO technology to the water content measurement of in situ soil.However,all existing in situ applications of AHFO technology fail to consider the effect of soilesensor contact quality on water content measurements,limiting potential for the wider application of AHFO technology.To address this issue,the authors propose a method for determining the soilesensor thermal contact resistance based on the principle of an infinite cylindrical heat source.This is then used to establish an AHFO water content measurement technology that considers the thermal contact resistance.The reliability and validity of the new measurement technology are explored through a laboratory test and a field case study,and the spatial-temporal evolution of the soil water content in the case is revealed.The results demonstrate that method for determining the soilesensor thermal contact resistance is highly effective and applicable to all types of soils.This method requires only the moisture content,dry density,and thermal response of the in situ soil to be obtained.In the field case,the measurement error of soil water content between the AHFO method,which takes into account the thermal contact resistance,and the neutron scattering method is only 0.011.The water content of in situ soil exhibits a seasonal variation,with an increase in spring and autumn and a decrease in summer and winter.Furthermore,the response of shallow soils to precipitation and evaporation is significant.These findings contribute to the enhancement of the accuracy of the AHFO technology in the measurement of the water content of in situ soils,thereby facilitating the dissemination and utilization of this technology.展开更多
Stainless steels have received wide attention as a substitute material for bipolar plates in high temperature proton exchange membrane fuel cell(HT-PEMFC).In the present work,the CrN,CrAlN and multilayer CrN/CrAlN coa...Stainless steels have received wide attention as a substitute material for bipolar plates in high temperature proton exchange membrane fuel cell(HT-PEMFC).In the present work,the CrN,CrAlN and multilayer CrN/CrAlN coatings were deposited on 316 L SS to increase the corrosion resistance and decrease the interfacial contact resistance.The deposited coatings exhibited face centered cubic phase structure and it was verified from the X-ray diffraction pattern.X-ray photo electron spectroscopy results showed the formation of both CrN and CrAlN layers on 316 L SS.CrN/CrAlN coating is more helpful in water management due to low surface roughness and high contact angle in the HT-PEMFC environment.The corrosion resistance behavior of all the samples were studied in 85%H_(3)PO_(4)solution at 140℃purged with H_(2)(HT-PEMFC anode)and O_(2)(HT-PEMFC cathode)gases.The results showed that all the coatings considerably improved the performance of 316 L SS and superior corrosion resistance was observed for CrN/CrAlN multilayer coating,whose protective efficiency was 98.12%and 96.14%in the two simulated HT-PEMFC environments.The results of electrochemical impedance spectroscopic studies demonstrated higher impedance for CrN/CrAlN coating.Surface morphological studies performed after corrosion studies revealed that protection ability of CrN/CrAlN coating still remained acceptable.A very low interfacial contact resistance value of 6 mΩ cm^(2) at 140 N/cm;was observed for CrN/CrAlN coating.Moreover,after corrosion studies,the interfacial contact resistance value of CrN/CrAlN coated 316 L was much lower than that of CrN and CrAlN coatings due to the increased oxidation resistance.The maximum power density of about 0.93 W/cm^(2) at 2 A/cm^(2) and output voltage of 0.96 V was observed for CrN/CrAlN coating.展开更多
Porous materials can be found in a variety of geophysical and engineering applications.The existence of thermal contact resistance at the interface between bilayered saturated porous strata would result in a significa...Porous materials can be found in a variety of geophysical and engineering applications.The existence of thermal contact resistance at the interface between bilayered saturated porous strata would result in a significant temperature difference at the interface.An attempt is made to study the thermo-hydro-mechanical coupling dynamic response of bilayered saturated porous strata with thermal contact resistance and elastic wave impedance.The corresponding analytical solutions for the dynamic response of bilayered saturated porous strata under a harmonic thermal load are derived by the operator decomposition method,and their rationality is verified by comparing them with existing solutions.The influences of thermal contact resistance,thermal conductivity ratio,and porosity ratio on the dynamic response of bilayered saturated porous strata are systematically investigated.Outcomes disclose that with the increase of thermal contact resistance,the displacement,pore water pressure and stress decrease gradually,and the temperature jump at the interface between two saturated porous strata increases.展开更多
In this article, a numerical model combining conduction and radiation is developed based on two flux approximation to predict the heat transfer behavior of fibrous insulation used in thermal protection systems. Monte ...In this article, a numerical model combining conduction and radiation is developed based on two flux approximation to predict the heat transfer behavior of fibrous insulation used in thermal protection systems. Monte Carlo method is utilized to determine the modified radiative properties with experimentally measured transient external temperature as high as 1 000 K. It is found that the estimated radiative properties become time-independent after about t = 3 000 s. By comparing the predicted to the measured results in transient state, the contact resistance exerts significant influences upon the temperature distribution in the specimen. Results show that the averaged absolute deviation is 3.25% when contact resistance is neglected in heat transfer model, while 1.82% with no contact resistance.展开更多
Aiming at determining the thermal contact resistance of ball screws,a new analytical method combining the minimum excess principle with the MB fractal theory is proposed to estimate thermal contact resistance of ball ...Aiming at determining the thermal contact resistance of ball screws,a new analytical method combining the minimum excess principle with the MB fractal theory is proposed to estimate thermal contact resistance of ball screws considering microscopic fractal characteristics of contact surfaces.The minimum excess principle is employed for normal stress analysis.Moreover,the MB fractal theory is adopted for thermal contact resistance.The effectiveness of the proposed method is validated by self-designed experiment.The comparison between theoretical and experimental results demonstrates that thermal contact resistance of ball screws can be obtained by the proposed method.On this basis,effects of fractal parameters on thermal contact resistance of ball screws are discussed.Moreover,effects of the axial load on thermal contact resistance of ball screws are also analyzed.The conclusion can be drawn that the thermal contact resistance decreases along with the fractal dimension D increase and it increases along with the scale parameter G increase,and thermal contact resistance of ball screws is retained almost constant along with axial load increase before the preload of the right nut turns into zero in value.The application of the proposed method is also conducted and validated by the temperature measurement on a self-designed test bed.展开更多
The contact resistance between the armature and rails is an important indicator of the contact characteristics in electromagnetic launches.As the contact resistance depends not only on the contact state but also on th...The contact resistance between the armature and rails is an important indicator of the contact characteristics in electromagnetic launches.As the contact resistance depends not only on the contact state but also on the contact stress and temperature,there are some limitations in analyzing the contact characteristics using only the contact resistance.In this paper,the contact characteristics of the augmented railgun are analyzed by the combination of contact resistance and sliding friction coefficient.Firstly,the theoretical calculation model of the contact resistance and friction coefficient of the augmented electromagnetic railgun is established.Then the contact resistance and friction coefficient are calculated by the measured values of the muzzle voltage,rail current and armature displacement.Finally,the contact characteristics are analyzed according to the features of the waveforms of the contact resistance and the friction coefficient,and the analysis conclusions are verified by experimental rail images.The results showed that:the aluminum melt film gradually formed on the contact surface reduces the contact resistance and the friction coefficient;the wear and erosion of the armature cause deterioration of the contact state;after the transition,the reliability of the sliding contact between the armature and rails decreases,resulting in an increase in contact resistance.展开更多
Poly(methyl methacrylate)(PMMA) is widely used for graphene transfer and device fabrication.However,it inevitably leaves a thin layer of polymer residues after acetone rinsing and leads to dramatic degradation of devi...Poly(methyl methacrylate)(PMMA) is widely used for graphene transfer and device fabrication.However,it inevitably leaves a thin layer of polymer residues after acetone rinsing and leads to dramatic degradation of device performance.How to eliminate contamination and restore clean surfaces of graphene is still highly demanded.In this paper,we present a reliable and position-controllable method to remove the polymer residues on graphene films by laser exposure.Under proper laser conditions,PMMA residues can be substantially reduced without introducing defects to the underlying graphene.Furthermore,by applying this laser cleaning technique to the channel and contacts of graphene fieldeffect transistors(GFETs),higher carrier mobility as well as lower contact resistance can be realized.This work opens a way for probing intrinsic properties of contaminant-free graphene and fabricating high-performance GFETs with both clean channel and intimate graphene/metal contact.展开更多
Thermal contact resistance plays a very important role in heat transfer efficiency and thermomechanical coupling response between two materials,and a common method to reduce the thermal contact resistance is to fill a...Thermal contact resistance plays a very important role in heat transfer efficiency and thermomechanical coupling response between two materials,and a common method to reduce the thermal contact resistance is to fill a soft interface material between these two materials.A testing system of high temperature thermal contact resistance based on INSTRON 8874 is established in the present paper,which can achieve 600 C at the interface.Based on this system,the thermal contact resistance between superalloy GH600 material and three-dimensional braid C/C composite material is experimentally investigated,under different interface pressures,interface roughnesses and temperatures,respectively.At the same time,the mechanism of reducing the thermal contact resistance with carbon fiber sheet as interface material is experimentally investigated.Results show that the present testing system is feasible in the experimental research of high temperature thermal contact resistance.展开更多
A genetic algorithm （GA） was studied to simultaneously determine the thermal transport properties and the contact resistance of thin films deposited on a thick substrate. A pulsed photothermal reflectance （PPR） sy...A genetic algorithm （GA） was studied to simultaneously determine the thermal transport properties and the contact resistance of thin films deposited on a thick substrate. A pulsed photothermal reflectance （PPR） system was employed for the measurements. The GA was used to extract the thermal properties. Measurements were performed on SiO2 thin films of different thicknesses on silicon substrate. The results show that the GA accompanied with the PPR system is useful for the simultaneous determination of thermal properties of thin films on a substrate.展开更多
To obtain thermal contact resistance（TCR） between the vertical double-diffused metal-oxide-semiconductor（VDMOS） and the heat sink, we derived the relationship between the total thermal resistance and the contact f...To obtain thermal contact resistance（TCR） between the vertical double-diffused metal-oxide-semiconductor（VDMOS） and the heat sink, we derived the relationship between the total thermal resistance and the contact force imposed on the VDMOS. The total thermal resistance from the chip to the heat sink is measured under different contact forces, and the TCR can be extracted nondestructively from the derived relationship. Finally, the experimental results are compared with the simulation results.展开更多
In this work, a method based on scanning Kelvin probe microscopy is proposed to separately extract source/drain（S/D） series resistance in operating amorphous indium–gallium–zinc–oxide（a-IGZO） thin-film transist...In this work, a method based on scanning Kelvin probe microscopy is proposed to separately extract source/drain（S/D） series resistance in operating amorphous indium–gallium–zinc–oxide（a-IGZO） thin-film transistors. The asymmetry behavior of S/D contact resistance is deduced and the underlying physics is discussed. The present results suggest that the asymmetry of S/D contact resistance is caused by the difference in bias conditions of the Schottky-like junction at the contact interface induced by the parasitic reaction between contact metal and a-IGZO. The overall contact resistance should be determined by both the bulk channel resistance of the contact region and the interface properties of the metalsemiconductor junction.展开更多
This paper investigates the distribution of contact resistance of the aluminum alloy in the squeeze stage. A new method of measuring path＇ s resistance is proposed firstly. Contact resistances are calculated accurate...This paper investigates the distribution of contact resistance of the aluminum alloy in the squeeze stage. A new method of measuring path＇ s resistance is proposed firstly. Contact resistances are calculated accurately by the systems of 5 linear equations and solutions show that three contact resistances are different. The probability density functions of contact resistance in workpiece/workpiece（ W/W） and upper electrode/workpiece（ E/W） show that the curve shape has steeper peak and heavier tail than that of the normal distribution. Non-parameter hypothesis test is performed and the result shows that R2 , R4 reject the normal distribution using chi-square and kolmogoroo statistic D method. Therefore, the Asymmetric Laplace distribution is fitted to empirical distributions and is applied to quantify the influence of random contact resistance. The result illustrates that AL distribution is very close to contact resistance of W/W and upper E/W and normal distribution has some deviation. The paper is helpful to research the initial nugget conditions, weldability and the transient multi-coupling field.展开更多
Based on the electrical contact and arc theory, the experiments on contact resistance characteristics of electrical contacts are carried out, by analyzing the experimental results, some conclusions of contact resistan...Based on the electrical contact and arc theory, the experiments on contact resistance characteristics of electrical contacts are carried out, by analyzing the experimental results, some conclusions of contact resistance characteristics have been obtained in this paper.展开更多
Reducing the contact resistance without degrading the mobility property is crucial to achieve high-performance graphene field effect transistors. Also, the idea of modifying the graphene surface by etching away the de...Reducing the contact resistance without degrading the mobility property is crucial to achieve high-performance graphene field effect transistors. Also, the idea of modifying the graphene surface by etching away the deposited metal provides a new angle to achieve this goal. We exploit this idea by providing a new process method which reduces the contact resistance from 597Ω ·μm to sub 200 Ω ·μm while no degradation of mobility is observed in the devices. This simple process method avoids the drawbacks of uncontrollability, ineffectiveness, and trade-off with mobility which often exist in the previously proposed methods.展开更多
The arc erosion under medium direct currents in the argon flow was tested on tungsten-copper（W-Cu） contacts which were processed by hot extrusion and heat treatment. The scanning electron microscopy（SEM） and trans...The arc erosion under medium direct currents in the argon flow was tested on tungsten-copper（W-Cu） contacts which were processed by hot extrusion and heat treatment. The scanning electron microscopy（SEM） and transmission electron microscopy（TEM） were used to study the microstructure of the W-Cu powders and compacts. The contact resistance, arcing energy, and arcing time were continuously measured by JF04C contact materials test system. Changes in tungsten-copper contact surface were observed by SEM. The test results showed that the arcing time and arcing energy all increase with current and voltage, but the changes of average contact resistance are more complicated. For a short arcing time, the average contact resistance decreases with increasing current due to the vaporization of Cu. However, for a longer arcing time, it slightly increases due to the formation of high resistant films, compound copper tungsten. The formation of compound copper tungsten was confirmed by the increased Rc kept in the range from 1.1 to 1.6 mΩ. The compound copper tungsten is first exposed with a tungsten and copper-rich surface, and then totally exposed due to evaporation of copper from the surface. At last a stabilized surface is created and the crystals decrease from 8 μm to 2 μm caused by the arc erosion.展开更多
We report on an improved metal-graphene ohmic contact in bilayer epitaxial graphene on a SiC substrate with contact resistance below 0.1 Ω.mm. Monolayer and bilayer epitaxial graphenes are prepared on a 4HoSiC substr...We report on an improved metal-graphene ohmic contact in bilayer epitaxial graphene on a SiC substrate with contact resistance below 0.1 Ω.mm. Monolayer and bilayer epitaxial graphenes are prepared on a 4HoSiC substrate in this work. Their contact resistances are measured by a transfer length method. An improved photoresist-free device fabrication method is used and is compared with the conventional device fabrication method. Compared with the monolayer graphene, the contact resistance Rc of bilayer graphene improves from an average of 0.24Ω·mm to 0. 1 Ωmm. Ohmic contact formation mechanism analysis by Landauer＇s approach reveals that the obtained low ohmic contact resistance in bilayer epitaxial graphene is due to their high carrier density high carrier transmission probability, and p-type doping introduced by contact metal Au.展开更多
基金Projects(42477162,52108347,52178371,52168046,52178321,52308383)supported by the National Natural Science Foundation of ChinaProjects(2023C03143,2022C01099,2024C01219,2022C03151)supported by the Zhejiang Key Research and Development Plan,China+6 种基金Project(LQ22E080010)supported by the Exploring Youth Project of Zhejiang Natural Science Foundation,ChinaProject(LR21E080005)supported by the Outstanding Youth Project of Natural Science Foundation of Zhejiang Province,ChinaProject(2022M712964)supported by the Postdoctoral Science Foundation of ChinaProject(2023AFB008)supported by the Natural Science Foundation of Hubei Province for Youth,ChinaProject(202203)supported by Engineering Research Centre of Rock-Soil Drilling&Excavation and Protection,Ministry of Education,ChinaProject(202305-2)supported by the Science and Technology Project of Zhejiang Provincial Communication Department,ChinaProject(2021K256)supported by the Construction Research Founds of Department of Housing and Urban-Rural Development of Zhejiang Province,China。
文摘This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi analytical solutions of temperature increment and displacement of multi-layered composite structures are obtained by using the Laplace transform method,upon which the effects of thermal resistance coefficient,partition coefficient,thermal conductivity ratio and heat capacity ratio on the responses are studied.The results show that the generalized imperfect thermal contact model can realistically describe the imperfect thermal contact problem.Accordingly,it may degenerate into other thermal contact models by adjusting the thermal resistance coefficient and partition coefficient.
基金the financial support of Natural Science Foundation of Hunan Province(2023JJ40261).
文摘The mass transport and ohmic losses in proton exchange membrane fuel cells(PEMFCs)is significantly influenced by the channel to rib width ratio(CRWR),particularly when accounting for the interfacial contact resistance between bipolar plates(BPs)and gas diffusion layers(GDLs)(ICRBP-GDL).Both the determination of the optimal CRWR value and the development of an efficient flow field structure are significantly influenced by ICRBP-GDLs.To investigate this,three-dimensional numerical models were developed,revealing that selecting an optimal CRWR tailored to specific ICRBP-GDL values can effectively balance mass transport and ohmic losses.Building on this insight,a novel island two-dimensional flow field design is proposed,demonstrating the ability to enhance oxygen transport to the catalyst layer(CL)and achieve a more uniform oxygen distribution without increasing ohmic losses.Compared to conventional straight and serpentine flow fields,the island flow field improves output power density by 4.5%and 3.5%,respectively,while reducing the liquid water coverage ratio by 30%.Additionally,the study identifies optimal CRWR values for conventional flow fields corresponding to ICRBP-GDLs of 2.5,5,10,20,and 40 mΩ·cm^(2) as 1.5,1.5,1.0,0.67,and 0.43,respectively.For the island flow field,the optimal CRWRs are consistently smaller-1.5,1.0,0.67,0.43,and 0.43-due to its superior mass transfer capability.This work provides a valuable framework for optimizing flow field designs to achieve improved PEMFC performance.
基金by the Natural Science Foundation of Shandong Province,China(No.ZR2023QE159).
文摘This paper investigates interfacial heat transfer characteristics in amulti-layer structure under ultra-high heat flux conditions,focusing on thermal contact resistance(TCR)between adjacent layers.Athree-layer computational model with dual rough interfaces was developed to systematically analyze the synergistic effects of interfacial pressure,surface emissivity,and thermal interface materials(TIMs).Surface reconstruction using experimental measurement data generated two representative roughness models to quantify the impact of surface roughness on heat dissipation.Numerical simulations demonstrate that the absence of TIMs leads to insufficient thermal dissipation capacity under ultra-high heat flux conditions.Compared to TIMapplication,merely increasing the convective heat transfer coefficient shows limited effectiveness in enhancing heat dissipation efficiency.
基金the Basic Science Research Program through the National Research Foundation(NRF)of Korea funded by the Ministry of Education,Science,and Technology(No.2022R1A2C1004437)the Ministry of Science and ICT(MSIT)of Korea Government(No.2022M3J7A1062940)。
文摘In this study,the effects of stacked nanosheets and the surrounding interphase zone on the resistance of the contact region between nanosheets and the tunneling conductivity of samples are evaluated with developed equations superior to those previously reported.The contact resistance and nanocomposite conductivity are modeled by several influencing factors,including stack properties,interphase depth,tunneling size,and contact diameter.The developed model's accuracy is verified through numerous experimental measurements.To further validate the models and establish correlations between parameters,the effects of all the variables on contact resistance and nanocomposite conductivity are analyzed.Notably,the contact resistance is primarily dependent on the polymer tunnel resistivity,contact area,and tunneling size.The dimensions of the graphene nanosheets significantly influence the conductivity,which ranges from 0 S/m to90 S/m.An increased number of nanosheets in stacks and a larger gap between them enhance the nanocomposite's conductivity.Furthermore,the thicker interphase and smaller tunneling size can lead to higher sample conductivity due to their optimistic effects on the percolation threshold and network efficacy.
基金supported by the National Natural Science Foundation of China(Grant Nos.42307189 and 42030701)the China Postdoctoral Science Foundation(Grant No.2023M740974).
文摘The actively heated fiber-optic(AHFO)technology has become emerged as a research focus due to its advantages of distributed,real-time measurement and good durability.These attributes have led to the gradual application of AHFO technology to the water content measurement of in situ soil.However,all existing in situ applications of AHFO technology fail to consider the effect of soilesensor contact quality on water content measurements,limiting potential for the wider application of AHFO technology.To address this issue,the authors propose a method for determining the soilesensor thermal contact resistance based on the principle of an infinite cylindrical heat source.This is then used to establish an AHFO water content measurement technology that considers the thermal contact resistance.The reliability and validity of the new measurement technology are explored through a laboratory test and a field case study,and the spatial-temporal evolution of the soil water content in the case is revealed.The results demonstrate that method for determining the soilesensor thermal contact resistance is highly effective and applicable to all types of soils.This method requires only the moisture content,dry density,and thermal response of the in situ soil to be obtained.In the field case,the measurement error of soil water content between the AHFO method,which takes into account the thermal contact resistance,and the neutron scattering method is only 0.011.The water content of in situ soil exhibits a seasonal variation,with an increase in spring and autumn and a decrease in summer and winter.Furthermore,the response of shallow soils to precipitation and evaporation is significant.These findings contribute to the enhancement of the accuracy of the AHFO technology in the measurement of the water content of in situ soils,thereby facilitating the dissemination and utilization of this technology.
基金the financial assistance received from Science and Engineering Research Board(SERB PDF/2017/002594),New Delhi,India。
文摘Stainless steels have received wide attention as a substitute material for bipolar plates in high temperature proton exchange membrane fuel cell(HT-PEMFC).In the present work,the CrN,CrAlN and multilayer CrN/CrAlN coatings were deposited on 316 L SS to increase the corrosion resistance and decrease the interfacial contact resistance.The deposited coatings exhibited face centered cubic phase structure and it was verified from the X-ray diffraction pattern.X-ray photo electron spectroscopy results showed the formation of both CrN and CrAlN layers on 316 L SS.CrN/CrAlN coating is more helpful in water management due to low surface roughness and high contact angle in the HT-PEMFC environment.The corrosion resistance behavior of all the samples were studied in 85%H_(3)PO_(4)solution at 140℃purged with H_(2)(HT-PEMFC anode)and O_(2)(HT-PEMFC cathode)gases.The results showed that all the coatings considerably improved the performance of 316 L SS and superior corrosion resistance was observed for CrN/CrAlN multilayer coating,whose protective efficiency was 98.12%and 96.14%in the two simulated HT-PEMFC environments.The results of electrochemical impedance spectroscopic studies demonstrated higher impedance for CrN/CrAlN coating.Surface morphological studies performed after corrosion studies revealed that protection ability of CrN/CrAlN coating still remained acceptable.A very low interfacial contact resistance value of 6 mΩ cm^(2) at 140 N/cm;was observed for CrN/CrAlN coating.Moreover,after corrosion studies,the interfacial contact resistance value of CrN/CrAlN coated 316 L was much lower than that of CrN and CrAlN coatings due to the increased oxidation resistance.The maximum power density of about 0.93 W/cm^(2) at 2 A/cm^(2) and output voltage of 0.96 V was observed for CrN/CrAlN coating.
基金Projects(52108347,52178371)supported by the National Natural Science Foundation of ChinaProject(LQ22E080010)supported by the Exploring Youth Project of Zhejiang Natural Science Foundation,China。
文摘Porous materials can be found in a variety of geophysical and engineering applications.The existence of thermal contact resistance at the interface between bilayered saturated porous strata would result in a significant temperature difference at the interface.An attempt is made to study the thermo-hydro-mechanical coupling dynamic response of bilayered saturated porous strata with thermal contact resistance and elastic wave impedance.The corresponding analytical solutions for the dynamic response of bilayered saturated porous strata under a harmonic thermal load are derived by the operator decomposition method,and their rationality is verified by comparing them with existing solutions.The influences of thermal contact resistance,thermal conductivity ratio,and porosity ratio on the dynamic response of bilayered saturated porous strata are systematically investigated.Outcomes disclose that with the increase of thermal contact resistance,the displacement,pore water pressure and stress decrease gradually,and the temperature jump at the interface between two saturated porous strata increases.
基金National High-tech Research and Development Program(2006AA705317)
文摘In this article, a numerical model combining conduction and radiation is developed based on two flux approximation to predict the heat transfer behavior of fibrous insulation used in thermal protection systems. Monte Carlo method is utilized to determine the modified radiative properties with experimentally measured transient external temperature as high as 1 000 K. It is found that the estimated radiative properties become time-independent after about t = 3 000 s. By comparing the predicted to the measured results in transient state, the contact resistance exerts significant influences upon the temperature distribution in the specimen. Results show that the averaged absolute deviation is 3.25% when contact resistance is neglected in heat transfer model, while 1.82% with no contact resistance.
基金Projects(51875008,51505012,51575014)supported by the National Natural Science Foundation of ChinaProject supported by the China Scholarship Council
文摘Aiming at determining the thermal contact resistance of ball screws,a new analytical method combining the minimum excess principle with the MB fractal theory is proposed to estimate thermal contact resistance of ball screws considering microscopic fractal characteristics of contact surfaces.The minimum excess principle is employed for normal stress analysis.Moreover,the MB fractal theory is adopted for thermal contact resistance.The effectiveness of the proposed method is validated by self-designed experiment.The comparison between theoretical and experimental results demonstrates that thermal contact resistance of ball screws can be obtained by the proposed method.On this basis,effects of fractal parameters on thermal contact resistance of ball screws are discussed.Moreover,effects of the axial load on thermal contact resistance of ball screws are also analyzed.The conclusion can be drawn that the thermal contact resistance decreases along with the fractal dimension D increase and it increases along with the scale parameter G increase,and thermal contact resistance of ball screws is retained almost constant along with axial load increase before the preload of the right nut turns into zero in value.The application of the proposed method is also conducted and validated by the temperature measurement on a self-designed test bed.
文摘The contact resistance between the armature and rails is an important indicator of the contact characteristics in electromagnetic launches.As the contact resistance depends not only on the contact state but also on the contact stress and temperature,there are some limitations in analyzing the contact characteristics using only the contact resistance.In this paper,the contact characteristics of the augmented railgun are analyzed by the combination of contact resistance and sliding friction coefficient.Firstly,the theoretical calculation model of the contact resistance and friction coefficient of the augmented electromagnetic railgun is established.Then the contact resistance and friction coefficient are calculated by the measured values of the muzzle voltage,rail current and armature displacement.Finally,the contact characteristics are analyzed according to the features of the waveforms of the contact resistance and the friction coefficient,and the analysis conclusions are verified by experimental rail images.The results showed that:the aluminum melt film gradually formed on the contact surface reduces the contact resistance and the friction coefficient;the wear and erosion of the armature cause deterioration of the contact state;after the transition,the reliability of the sliding contact between the armature and rails decreases,resulting in an increase in contact resistance.
基金the National Basic Research Program of China(Grant No.2013CBA01604)the National Science and Technology Major Project of China(Grant No.2011ZX02707)
文摘Poly(methyl methacrylate)(PMMA) is widely used for graphene transfer and device fabrication.However,it inevitably leaves a thin layer of polymer residues after acetone rinsing and leads to dramatic degradation of device performance.How to eliminate contamination and restore clean surfaces of graphene is still highly demanded.In this paper,we present a reliable and position-controllable method to remove the polymer residues on graphene films by laser exposure.Under proper laser conditions,PMMA residues can be substantially reduced without introducing defects to the underlying graphene.Furthermore,by applying this laser cleaning technique to the channel and contacts of graphene fieldeffect transistors(GFETs),higher carrier mobility as well as lower contact resistance can be realized.This work opens a way for probing intrinsic properties of contaminant-free graphene and fabricating high-performance GFETs with both clean channel and intimate graphene/metal contact.
基金supported by the Fundamental Research Funds for the Central Universities (FRF-BR-10-007A and FRF-AS-09-001A)the National Natural Science Foundation of China (10872104)
文摘Thermal contact resistance plays a very important role in heat transfer efficiency and thermomechanical coupling response between two materials,and a common method to reduce the thermal contact resistance is to fill a soft interface material between these two materials.A testing system of high temperature thermal contact resistance based on INSTRON 8874 is established in the present paper,which can achieve 600 C at the interface.Based on this system,the thermal contact resistance between superalloy GH600 material and three-dimensional braid C/C composite material is experimentally investigated,under different interface pressures,interface roughnesses and temperatures,respectively.At the same time,the mechanism of reducing the thermal contact resistance with carbon fiber sheet as interface material is experimentally investigated.Results show that the present testing system is feasible in the experimental research of high temperature thermal contact resistance.
基金the National Natural Science Foundation of China under Grant Nos. 59995550-5 , 90207003.
文摘A genetic algorithm （GA） was studied to simultaneously determine the thermal transport properties and the contact resistance of thin films deposited on a thick substrate. A pulsed photothermal reflectance （PPR） system was employed for the measurements. The GA was used to extract the thermal properties. Measurements were performed on SiO2 thin films of different thicknesses on silicon substrate. The results show that the GA accompanied with the PPR system is useful for the simultaneous determination of thermal properties of thin films on a substrate.
基金Project supported by the National Natural Science Foundation of China(Grant No.61204081)
文摘To obtain thermal contact resistance（TCR） between the vertical double-diffused metal-oxide-semiconductor（VDMOS） and the heat sink, we derived the relationship between the total thermal resistance and the contact force imposed on the VDMOS. The total thermal resistance from the chip to the heat sink is measured under different contact forces, and the TCR can be extracted nondestructively from the derived relationship. Finally, the experimental results are compared with the simulation results.
基金Project supported by the Key Industrial R&D Program of Jiangsu Province,China(Grant No.BE2015155)the Priority Academic Program Development of Higher Education Institutions of Jiangsu Province,Chinathe Fundamental Research Funds for the Central Universities,China(Grant No.021014380033)
文摘In this work, a method based on scanning Kelvin probe microscopy is proposed to separately extract source/drain（S/D） series resistance in operating amorphous indium–gallium–zinc–oxide（a-IGZO） thin-film transistors. The asymmetry behavior of S/D contact resistance is deduced and the underlying physics is discussed. The present results suggest that the asymmetry of S/D contact resistance is caused by the difference in bias conditions of the Schottky-like junction at the contact interface induced by the parasitic reaction between contact metal and a-IGZO. The overall contact resistance should be determined by both the bulk channel resistance of the contact region and the interface properties of the metalsemiconductor junction.
基金This research was supported by National Natural Science Foundation of China(No50575159)Project of Chinese Ministry ofEducation(No106049, 20060056058)Natural Science Foundation of Tianjin (06YFJMJC03400)
文摘This paper investigates the distribution of contact resistance of the aluminum alloy in the squeeze stage. A new method of measuring path＇ s resistance is proposed firstly. Contact resistances are calculated accurately by the systems of 5 linear equations and solutions show that three contact resistances are different. The probability density functions of contact resistance in workpiece/workpiece（ W/W） and upper electrode/workpiece（ E/W） show that the curve shape has steeper peak and heavier tail than that of the normal distribution. Non-parameter hypothesis test is performed and the result shows that R2 , R4 reject the normal distribution using chi-square and kolmogoroo statistic D method. Therefore, the Asymmetric Laplace distribution is fitted to empirical distributions and is applied to quantify the influence of random contact resistance. The result illustrates that AL distribution is very close to contact resistance of W/W and upper E/W and normal distribution has some deviation. The paper is helpful to research the initial nugget conditions, weldability and the transient multi-coupling field.
文摘Based on the electrical contact and arc theory, the experiments on contact resistance characteristics of electrical contacts are carried out, by analyzing the experimental results, some conclusions of contact resistance characteristics have been obtained in this paper.
基金Project by the National Science and Technology Major Project,China(Grant No.2011ZX02707.3)the National Natural Science Foundation of China(Grant No.61136005)+1 种基金the Chinese Academy of Sciences(Grant No.KGZD-EW-303)the Project of Beijing Municipal Science and Technology Commission,China(Grant No.Z151100003515003)
文摘Reducing the contact resistance without degrading the mobility property is crucial to achieve high-performance graphene field effect transistors. Also, the idea of modifying the graphene surface by etching away the deposited metal provides a new angle to achieve this goal. We exploit this idea by providing a new process method which reduces the contact resistance from 597Ω ·μm to sub 200 Ω ·μm while no degradation of mobility is observed in the devices. This simple process method avoids the drawbacks of uncontrollability, ineffectiveness, and trade-off with mobility which often exist in the previously proposed methods.
文摘The arc erosion under medium direct currents in the argon flow was tested on tungsten-copper（W-Cu） contacts which were processed by hot extrusion and heat treatment. The scanning electron microscopy（SEM） and transmission electron microscopy（TEM） were used to study the microstructure of the W-Cu powders and compacts. The contact resistance, arcing energy, and arcing time were continuously measured by JF04C contact materials test system. Changes in tungsten-copper contact surface were observed by SEM. The test results showed that the arcing time and arcing energy all increase with current and voltage, but the changes of average contact resistance are more complicated. For a short arcing time, the average contact resistance decreases with increasing current due to the vaporization of Cu. However, for a longer arcing time, it slightly increases due to the formation of high resistant films, compound copper tungsten. The formation of compound copper tungsten was confirmed by the increased Rc kept in the range from 1.1 to 1.6 mΩ. The compound copper tungsten is first exposed with a tungsten and copper-rich surface, and then totally exposed due to evaporation of copper from the surface. At last a stabilized surface is created and the crystals decrease from 8 μm to 2 μm caused by the arc erosion.
基金Supported by the National Natural Science Foundation of China under Grant No 61306006
文摘We report on an improved metal-graphene ohmic contact in bilayer epitaxial graphene on a SiC substrate with contact resistance below 0.1 Ω.mm. Monolayer and bilayer epitaxial graphenes are prepared on a 4HoSiC substrate in this work. Their contact resistances are measured by a transfer length method. An improved photoresist-free device fabrication method is used and is compared with the conventional device fabrication method. Compared with the monolayer graphene, the contact resistance Rc of bilayer graphene improves from an average of 0.24Ω·mm to 0. 1 Ωmm. Ohmic contact formation mechanism analysis by Landauer＇s approach reveals that the obtained low ohmic contact resistance in bilayer epitaxial graphene is due to their high carrier density high carrier transmission probability, and p-type doping introduced by contact metal Au.
