Showing papers on "Thermal contact conductance published in 2009"
TL;DR: In this paper, the thermal contact resistance between graphene and silicon dioxide was measured using a differential 3ω method and the sample thicknesses were 1.2, 1.5, 2.8, and 3.0 nm, as determined by atomic force microscopy.
Abstract: The thermal contact resistance between graphene and silicon dioxide was measured using a differential 3ω method. The sample thicknesses were 1.2 (single-layer graphene), 1.5, 2.8, and 3.0 nm, as determined by atomic force microscopy. All samples exhibited approximately the same temperature trend from 42 to 310 K, with no clear thickness dependence. The contact resistance at room temperature ranges from 5.6×10−9 to 1.2×10−8 m2 K/W, which is significantly lower than previous measurements involving related carbon materials. These results underscore graphene’s potential for applications in microelectronics and thermal management structures.
334 citations
TL;DR: A frequency-domain thermoreflectance method for measuring the thermal properties of homogenous materials and submicron thin films and its sensitivity to various thermal properties is given, along with results from measurements of several standard materials over a wide range of thermal diffusivities.
Abstract: A frequency-domain thermoreflectance method for measuring the thermal properties of homogenous materials and submicron thin films is described. The method can simultaneously determine the thermal conductivity and heat capacity of a sample, provided the thermal diffusivity is greater, similar3x10(-6) m(2)/s, and can also simultaneously measure in-plane and cross-plane thermal conductivities, as well the thermal boundary conductance between material layers. Two implementations are discussed, one based on an ultrafast pulsed laser system and one based on continuous-wave lasers. The theory of the method and an analysis of its sensitivity to various thermal properties are given, along with results from measurements of several standard materials over a wide range of thermal diffusivities. We obtain specific heats and thermal conductivities in good agreement with literature values, and also obtain the in-plane and cross-plane thermal conductivities for crystalline quartz.
329 citations
TL;DR: In this article, an analytical model of contact resistance (Rc) that accounts for the strength of the interfacial bonding is presented, where conductance/area is proportional to the square of the adhesion energy of the interface for weak bonding.
Abstract: Nanoparticles are typically in contact with another surface through weak van der Waals force. Thermal transport in these nanostructured systems is mainly limited by the contact resistance (Rc). Rc of nanoparticles have been typically calculated using the traditional acoustic or diffuse mismatch models, which assume very strong bond at the interface. In this paper, an analytical model of Rc that accounts for the strength of the interfacial bonding is presented. Conductance/area is proportional to the square of the adhesion energy of the interface for weak bonding and is the same as that given by traditional acoustic mismatch model for strong bonding.
235 citations
TL;DR: A non-contact Raman spectra shift method is introduced, by which the thermal conductivity (kappa) of an individual single-Walled carbon nanotube and a multi-walled carbonnanotube is measured.
Abstract: The thermal contact resistance is a difficult problem that has puzzled many researchers in measuring the intrinsic thermal conductivity of an individual carbon nanotube (CNT). To avoid this problem, a non-contact Raman spectra shift method is introduced, by which we have successfully measured the thermal conductivity (kappa) of an individual single-walled carbon nanotube and a multi-walled carbon nanotube. The measured kappa values are 2400 W m(-1) K(-1) and 1400 W m(-1) K(-1), respectively. The CNT was suspended over a trench and heated by electricity. The temperature difference between the middle and the two ends of the CNT indicated its intrinsic heat transfer capability. The temperature difference was determined by the temperature-induced shifts of its G band Raman spectra. This new method can eliminate the impact of the thermal contact resistance which was a Gordian knot in many previous measurements.
195 citations
TL;DR: In this article, the crystal structure of the measured CNT samples was characterized in detail using transmission electron microscopy (TEM) and the thermal conductance, diameter, and chirality were all determined on the same individual SWCNT, and the intrinsic thermal conductivity of individual single (S), double (D), and multi-walled (W) carbon nanotubes (CNTs) grown using thermal chemical vapor deposition between two suspended microthermometers are reported.
Abstract: Thermal conductance measurements of individual single- (S), double- (D), and multi- (M) walled (W) carbon nanotubes (CNTs) grown using thermal chemical vapor deposition between two suspended microthermometers are reported. The crystal structure of the measured CNT samples is characterized in detail using transmission electron microscopy (TEM). The thermal conductance, diameter, and chirality are all determined on the same individual SWCNT. The thermal contact resistance per unit length is obtained as 78―585 m K W ―1 for three as-grown 10―14 nm diameter MWCNTs on rough Pt electrodes, and decreases by more than 2 times after the deposition of amorphous platinum―carbon composites at the contacts. The obtained intrinsic thermal conductivity of approximately 42―48, 178―336, and 269― 343 W m ―1 K ―1 at room-temperature for the three MWCNT samples correlates well with TEM-observed defects spaced approximately 13, 20, and 29 nm apart, respectively; whereas the effective thermal conductivity is found to be limited by the thermal contact resistance to be about 600 W m ―1 K ―1 at room temperature for the as-grown DWCNT and SWCNT samples without the contact deposition.
173 citations
TL;DR: In this paper, the role of solid stiffness and the bonding strength across the interface on the interfacial thermal conductance between single-crystal silicon and amorphous polyethylene was investigated.
Abstract: We use nonequilibrium molecular dynamics simulation to elucidate the interfacial thermal conductance between single-crystal silicon and amorphous polyethylene. In particular, we investigate the role of solid stiffness and the bonding strength across the interface on the interfacial thermal conductance. Simulations of interfacial scattering of individual phonon wave packets indicate that neither diffuse mismatch model nor acoustic mismatch model describes the interfacial scattering process quantitatively. In general, transmission coefficients for longitudinal phonons are significantly higher than those for transverse phonons. We also observe that anharmonic processes can be important for interfacial conductance.
168 citations
TL;DR: In this paper, the authors reviewed the findings of recent research on the formation of solid splats by the impact of thermal spray particles on solid substrates and discussed methods of describing the substrate by characterizing both chemical (oxide layers) and surface topography, adsorbed and condensed contaminants.
Abstract: This paper reviews the findings of recent research on the formation of solid splats by the impact of thermal spray particles on solid substrates. It discusses methods of describing the substrate, by characterizing both chemical (oxide layers) and physical (surface topography, adsorbed and condensed contaminants) aspects. Recent experiments done to observe impact of thermal spray particle are surveyed and techniques used to photograph particle impact and measure cooling rates described. The use of numerical modeling to simulate impact and deformation of impacting particles is appraised. Two different break-up mechanisms are identified: solidification around the edges of splats; and perforations in the interior of thin liquid films created by droplet spreading without solidification. These two modes can be reproduced in numerical models by varying the value of thermal contact resistance between the splat and substrate. A simple criterion to predict the final splat shape is presented.
165 citations
TL;DR: In this paper, a model was developed to predict the thermal contact resistance of carbon nanotube (CNT) array interfaces with CNT arrays synthesized directly on substrate surfaces.
151 citations
TL;DR: It is found that when torsional strain is applied, the thermal conductivity drops as well, with significant reductions once the carbon nanotube begins to buckle, which could be used in developing novel thermal materials whose properties can be altered in situ.
Abstract: Carbon nanotubes are superior materials for thermal management and phononic device use due to their extremely high thermal conductivity and unique one-dimensional geometry. Here we report a systematic investigation of the effects of mechanical tensile, compressive and torsional strain on the thermal conductivity of single-walled carbon nanotubes using molecular dynamics simulation. In contrast to conventional predictions for solids, an unexpected dependence on the applied strain is revealed by the low-dimensional nature and tubular geometry of carbon nanotubes. Under tension, the thermal conductivity is reduced due to the softening of G-band phonon modes. Under compression—in contrast to the case for conventional theories for solids—geometric instabilities lower the thermal conductivity due to the scattering, shortening of the mean free path and interface resistance that arise from localized radial buckling. We find that when torsional strain is applied, the thermal conductivity drops as well, with significant reductions once the carbon nanotube begins to buckle. This thermomutability concept—the ability to control thermal properties by means of external cues—could be used in developing novel thermal materials whose properties can be altered in situ.
139 citations
TL;DR: In this paper, the experimental thermal conductivity estimated by the indirect relation \lambda = a\rhoC_p is presented as a function of the temperature, and the influence of heat treatment on the thermal conductivities of carbon fibers is also described.
122 citations
TL;DR: In this paper, the effects of various combinations of bolt configuration and clamping torque on the corresponding contact pressure distributions and performances of a single PEMFC and a 10-cell stack were investigated.
TL;DR: In this article, the authors used a contact impedance model to compare the contact impedance of aligned silver nanowire-polymer composites with that of aligned carbon nanotubes, which showed that the Young's modulus of the composite is the defining factor in the overall thermal impedance of these composites.
Abstract: Silver nanowire arrays embedded inside polycarbonate templates are investigated as a viable thermal interface material for electronic cooling applications. The composite shows an average thermal diffusivity value of 1.89×10−5 m2 s−1, which resulted in an intrinsic thermal conductivity of 30.3 W m−1 K−1. The nanowires’ protrusion from the film surface enables it to conform to the surface roughness to make a better thermal contact. This resulted in a 61% reduction in thermal impedance when compared with blank polymer. An ∼30 nm Au film on the top of the composite was found to act as a heat spreader, reducing the thermal impedance further by 35%. A contact impedance model was employed to compare the contact impedance of aligned silver nanowire-polymer composites with that of aligned carbon nanotubes, which showed that the Young’s modulus of the composite is the defining factor in the overall thermal impedance of these composites.
TL;DR: Spatially resolved Raman spectra of individual pristine suspended carbon nanotubes are observed under electrical heating, revealing the mechanism of thermal transport in these devices and enabling a direct estimate of thermal contact resistances and the spatial variation of thermal conductivity.
Abstract: Spatially resolved Raman spectra of individual pristine suspended carbon nanotubes are observed under electrical heating. The Raman G+ and G- bands show unequal temperature profiles. The preferential heating is more pronounced in short nanotubes (2 µm) than in long nanotubes (5 µm). These results are understood in terms of the decay and thermalization of nonequilibrium phonons, revealing the mechanism of thermal transport in these devices. The measurements also enable a direct estimate of thermal contact resistances and the spatial variation of thermal conductivity.
TL;DR: In this paper, the authors proposed a model of a network of discrete thermal resistances, where the effective thermal conductivity depends on three dimensionless morphological parameters: the volume fraction of solid phase, the mean coordination number, and the ratio of the size of necks between particles to the sizes of particles.
Abstract: Heat transfer between contacting solid particles in gas is localized about the points of contact because of the low thermal conductivity of gas. This suggests the model of a network of discrete thermal resistances. Thermal interaction of two particles in the zone of contact between them includes thermal conductivity in the solid phase as well as heat transfer through a gas gap between the particles, where the conductive heat transfer at higher distances from the center of the contact changes to the transition transfer and free molecular transfer near the contact center. In the framework of this approach the effective thermal conductivity depends on three dimensionless morphological parameters: the volume fraction of solid phase, the mean coordination number, and the ratio of the size of necks between particles to the size of particles. The physical properties of the phases are specified by the thermal conductivities of the solid and the gas, the adiabatic exponent of the gas, and the Knudsen number. The proposed model agrees with the experimental S curves of the effective thermal conductivity versus the logarithm of gas pressure. It also describes the experimental tendencies of increasing the effective thermal conductivity with the particle size and the volume fraction of solid. The model can be applied to powder beds with micron-sized particles as well as to packed beds with millimeter-sized particles in gas. Free molecular and transient regimes of heat transfer in the gas filling pores can be important even for millimeter-sized particles at atmospheric pressure when the Knudsen number is as low as ${10}^{\ensuremath{-}5}$. These rarefied gas phenomena are responsible for such a complicated behavior of the considered heterogeneous media. Their quantitative description gives the model, which does not contain fitting parameters.
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TL;DR: In this article, non-equilibrium molecular dynamics simulations were performed on Au-SAM (self-assembly monolayer)-Au junctions to study the thermal energy transport across the junctions.
Abstract: Non-equilibrium molecular dynamics (NEMD) simulations were performed on Au-SAM (self-assembly monolayer)-Au junctions to study the thermal energy transport across the junctions. Thermal conductance of the Au-SAM interfaces was calculated. Temperature effects, simulated external pressure effects, SAM molecule coverage effects and Au-SAM bond strength effects on the interfacial thermal conductance were studied. It was found that the interfacial thermal conductance increased with temperature increase at temperatures lower than 250K, but it did not have large changes at temperatures from 250K to 400K. Such a trend was found to be similar to experimental observations on similar junctions. The simulated external pressure did not affect the interfacial thermal conductance. SAM molecule coverage and Au-SAM bond strength were found to significantly affect on the thermal conductance. The vibration densities of state (VDOS) were calculated to explore the mechanism of thermal energy transport. Interfacial thermal resistance was found mainly due to the limited population of low-frequency vibration modes of the SAM molecule. Ballistic energy transport inside the SAM molecules was confirmed, and the anharmonicity played an important role in energy transport across the junctions. A heat pulse was imposed on the junction substrate, and heat dissipation inside the junction was studied. Analysis of the junction response to the heat pulse showed that the Au-SAM interfacial thermal resistance was much larger than the Au substrate and SAM resistances separately. This work showed that both the Au substrate and SAM molecules transported thermal energy efficiently, and it was the Au-SAM interfaces that dominated the thermal energy transport across the Au-SAM-Au junctions.
TL;DR: In this article, a semi-analytical solution procedure for transient heat transfer in composite mediums consisting of multi-layers within the framework of the dual phase lag model is presented, which is applicable to the classical Fourier heat diffusion, hyperbolic heat conduction, phonon-electron interaction, and phonon scattering models with perfect or imperfect contact and with layers of different materials.
TL;DR: In this article, the thermal boundary conductance is derived for the heat flow between the electrons in a metal and the phonons in an ionic crystal, where the image potential generated by the ion charges makes a regular pattern of surface charges on the surface of the metal.
Abstract: The thermal boundary conductance is derived for the heat flow between the electrons in a metal and the phonons in an ionic crystal. The image potential generated by the ion charges makes a regular pattern of surface charges on the surface of the metal. When the ions vibrate, these surface charges oscillate. Since the surface charges are the tails of the wave functions of the conduction electrons in the metal, the surface charges provide a matrix element between these electrons and the phonons in the insulator.
TL;DR: The role of TBR in controlling thermal conductivity at the nanoscale is analyzed by performing non-equilibrium molecular dynamics simulations to calculate Thermal conductivity of a range of Si-Ge multilayered structures with 1-3 periods, and with four different layer thicknesses, and finds that the TBR offered by the interface nearest to the hot reservoir is the highest.
Abstract: Nanoscale engineered materials with tailored thermal properties are desirable for applications such as highly efficient thermoelectric, microelectronic and optoelectronic devices. It has been shown earlier that by judiciously varying the interface thermal boundary resistance (TBR), thermal conductivity in nanostructures can be controlled. In the presented investigation, the role of TBR in controlling thermal conductivity at the nanoscale is analyzed by performing non-equilibrium molecular dynamics (NEMD) simulations to calculate thermal conductivity of a range of Si-Ge multilayered structures with 1-3 periods, and with four different layer thicknesses. The analyses are performed at three different temperatures (400, 600 and 800 K). As expected, the thermal conductivity of all layered structures increases with the increase in the number of periods as well as with the increase in the monolayer thickness. Invariably, we find that the TBR offered by the interface nearest to the hot reservoir is the highest. This effect is in contrast to the usual notion that each interface contributes equally to the heat transfer resistance in a layered structure. Findings also suggest that for high period structures the average TBR offered by the interfaces is not equal. Findings are used to derive an analytical expression that describes period-length-dependent thermal conductivity of multilayered structures.
TL;DR: In this article, a model of heat conduction for mono-sized spherical particulate media under stagnant gases based on the kinetic theory of gases, numerical modeling of Fourier's law of heat-conduction, theoretical constraints on the gas thermal conductivity at various Knudsen regimes, and laboratory measurements is presented.
Abstract: [1] We present a model of heat conduction for mono-sized spherical particulate media under stagnant gases based on the kinetic theory of gases, numerical modeling of Fourier's law of heat conduction, theoretical constraints on the gas thermal conductivity at various Knudsen regimes, and laboratory measurements. Incorporating the effect of the temperature allows for the derivation of the pore-filling gas conductivity and bulk thermal conductivity of samples using additional parameters (pressure, gas composition, grain size, and porosity). The radiative and solid-to-solid conductivities are also accounted for. Our thermal model reproduces the well-established bulk thermal conductivity dependency of a sample with the grain size and pressure and also confirms laboratory measurements finding that higher porosities generally lead to lower conductivities. It predicts the existence of the plateau conductivity at high pressure, where the bulk conductivity does not depend on the grain size. The good agreement between the model predictions and published laboratory measurements under a variety of pressures, temperatures, gas compositions, and grain sizes provides additional confidence in our results. On Venus, Earth, and Titan, the pressure and temperature combinations are too high to observe a soil thermal conductivity dependency on the grain size, but each planet has a unique thermal inertia due to their different surface temperatures. On Mars, the temperature and pressure combination is ideal to observe the soil thermal conductivity dependency on the average grain size. Thermal conductivity models that do not take the temperature and the pore-filling gas composition into account may yield significant errors.
TL;DR: In this paper, a system formed by a semi-infinite layer in contact with a finite one, that is excited by a modulated heat source is studied, and it is shown that a frequency range can be found in which the amplitude and phase of the spatial component of the oscillatory surface temperature show strong oscillations when the thermal relaxation time of the finite layer is close to its thermalization time.
TL;DR: In this article, a finite-element software (ABAQUS) was used to calculate the distribution of stress and contact pressure on all components of a standard solid oxide fuel cell repeat unit.
01 Jan 2009
TL;DR: In this paper, a finite element modeling of the continuous press hardening of car components using ultra high strength steel is presented, and the Numisheet 2008 benchmark problem BM03 is selected as the model problem to be solved.
Abstract: Summary: Presented is a methodology for finite element modeling of the continuous press hardening of car components using ultra high strength steel. The Numisheet 2008 benchmark problem BM03 [1] is selected as the model problem to be solved. LS-DYNA [2] has several features that are useful to numerically model hot sheet metal stamping, such as: (1) modeling high rate dynamics for press forming; (2) conduction, convection and radiation heat transfer; (3) tool-to-part contact conductance as a function of interface pressure; (4) material models that account for temperature dependent properties, phase change, phase fractions, and Vickers hardness prediction; and (5) a CFD solver for tool cooling.
TL;DR: In this article, an appraisal of thermal augmentation of thermoelectric module using nanofluid-based heat exchanger is presented, which is attributed to thermal contact resistance between the two components.
TL;DR: In this paper, a numerical model based on the detection of contacts and the evolution of heat transfers in particle flow has been developed by using discrete element method (DEM) for modeling the granular flow and heat transfer between particles during the discharge of a silo.
TL;DR: In this paper, defects in various cases are modeled by a nonlinear finite element method (FEM) to investigate the existence of interfaces, interfacial open and contacts in terms of thermal contact resistance, stress force nonlinearity, and optical discontinuity, in order to analyze their effects on the LED's thermal and optical performance.
Abstract: Defects in terms of voids, cracks, and delaminations are often generated in light-emitting diodes (LEDs) devices and modules. During various manufacturing processes, accelerated testing, inappropriate handling, and field applications, defects are most frequently induced in the early stage of process development. One loading is due to the nonuniform loads caused by temperature, moisture, and their gradients. In this research, defects in various cases are modeled by a nonlinear finite-element method (FEM) to investigate the existence of interfaces, interfacial open and contacts in terms of thermal contact resistance, stress force nonlinearity, and optical discontinuity, in order to analyze their effects on the LED's thermal and optical performance. The simulation results show that voids and delaminations in the die attachment would enhance the thermal resistance greatly and decrease the LED's light extraction efficiency, depending on the defects' sizes and locations generated in packaging.
TL;DR: In this paper, lock-in thermography is applied to image Joule heating and Peltier-type heat transport separately, and the results are interpreted in terms of diffusion and electron/hole drag contributions.
Abstract: Lock-in thermography is applied to image Joule heating and Peltier-type heat transport separately. Images obtained for a multicrystalline silicon solar cell are quantitatively evaluated using an integration method. The results are interpreted in terms of diffusion and electron/hole drag contributions. The approach presented is especially interesting where the thermal contact resistance to the sample is a problem and where versatility with respect to sample geometry is needed. A further advantage of the method is that it does not need any separate power or temperature calibration.
TL;DR: In this paper, the longitudinal thermal conductivity (TC) of an individual carbon fiber was measured using a T-type probe, where a hot wire was supplied with a constant direct current, whose ends were connected to heat sinks to maintain the initial temperature.
Abstract: A method was developed to measure the longitudinal thermal conductivity (TC) of an individual fibre using a T type probe. In the T type probe, a hot wire was supplied with a constant direct current, whose ends were connected to heat sinks to maintain the initial temperature. The test fibre was attached to the centre position of the hot wire at one end and the other end was connected to another heat sink. Based on a one-dimensional steady-state analysis of the heat conduction in the probe, the TC of the fibre and the thermal contact resistance at the junction between the fibre and the hot wire were simultaneously obtained, by changing the fibre length in the same contact condition at the junction. This method was verified by measuring the Pt wire as a reference sample, and good agreement was achieved between the measurement data and reference value. The TC of a pitch-based carbon fibre was obtained to be 490 W m −1 K −1 at room temperature, and the measurement uncertainty was analysed and compared with that of the previous T type probe method.
TL;DR: In this paper, the first attempt to combine heat conduction analysis, contact analysis, and transient analysis of disc brake squeal was made, where the contact pressure at the disc/pads interface is first computed, and the information is used to define friction-induced heat flux.
Abstract: This paper studies car disc brake squeal by transient analysis and details the first attempt to combine heat conduction analysis, contact analysis and transient analysis of disc brake squeal. The contact pressure at the disc/pads interface is first computed, and the information is used to define friction-induced heat flux. Its resultant heat conduction is then analysed. Finally, transient analysis is performed, considering the influence on squeal generation of contact pressure distribution affected by brake pad surface roughness and thermal deformation. A noticeable difference is found between the dynamic responses obtained with the thermal effect from those without the thermal effect.
TL;DR: An enhanced thermal conduction model for predicting convection dominated solid-liquid phase change is presented in this article, which relies entirely on the conduction equation for both the solid and liquid phases.
TL;DR: In this article, a package-level numerical simulation is developed to predict the on-chip hot spot cooling capability achievable with such a mini-contact enhanced TEC, focusing on the hot-spot temperature reduction associated with variations in mini contact size and thermoelectric element height.
Abstract: Shrinking feature size and increasing transistor density, combined with the high performance demanded from next-generation microprocessors, have led to on-chip high heat flux “hot spots,” which have emerged as the primary driver for thermal management of today's integrated circuit (IC) technology. This article describes the use of a mini-contact to enhance the cooling flux of a miniaturized thermoelectric cooler (TEC) for on-chip hot-spot remediation. A package-level numerical simulation is developed to predict the on-chip hot spot cooling capability achievable with such a mini-contact enhanced TEC. Attention is focused on the hot-spot temperature reduction associated with variations in mini-contact size and thermoelectric element height, as well as the parasitic effect from the thermal contact resistance introduced by the mini-contact. A preliminary experiment has been conducted to verify the numeric model and to demonstrate the effects of the mini-contact on hot-spot cooling.