Showing papers on "Thermal contact conductance published in 1999"

Thermal properties of lithium-ion battery and components

Abstract: Experimental thermal property data of the Sony US-18650 lithium-ion battery and components are presented, as well as thermal property measuring techniques. The properties in question are specific heat capacity (C{sub p}), thermal diffusivity ({alpha}), and thermal conductivity ({kappa}), in the presence and absence of electrolyte [1 M LiPF{sub 6} in ethylene carbonate-dimethyl carbonate (EC:DMC, 1:1 wt %)]. The heat capacity of the battery, C{sub p}, is 0.96 {+-} 0.02 J/g K at an open-circuit voltage (OCV) of 2.75 V, and 1.04 {+-} 0.02 J/g K at 3.75 V. The thermal conductivity, {kappa}, was calculated from {kappa} {identical_to} {alpha}{rho}C{sub p} where {alpha} was measured by a xenon-flash technique. In the absence of electrolyte, {kappa} increases with OCV, for both the negative electrode (NE) and the positive electrode (PE). For the NE, the increase is 26% as the OCV increases from 2.75 to 3.75 V, whereas for the PE the increase is only 5 to 6%. The dependence of both C{sub p} and {kappa} on OCV is explained qualitatively by considering the effect of lithiation and delithiation on the electron carrier density, which leads to n-type semiconduction in the graphitic NE material, but a change from semiconducting to metallic character in Li{submore » x}CoO{sub 2} PE material. The overall effect is an increase of C{sub p} and {kappa} with OCV. For {kappa} this dependence is eliminated by electrolyte addition, which, however, greatly increases the effective {kappa} of the layered battery components by lowering the thermal contact resistance. For both NE and PE, the in-plane {kappa} value (measured along layers) is nearly one order of magnitude higher than the cross-plane {kappa}. This is ascribed mostly to the high thermal conductivity of the current collectors and to a lesser extent to the orientation of particles in the layers of electrodes.« less

Thermal conductivity and diffusivity of wood.

Abstract: Transient simultaneous measurements of thermal conductivity and diffusivity of Swedish wood have been performed with the plane source technique on oven-dry hardwood (birch) samples at room temperature and at 100 °C. The influences of temperature, density, porosity and anisotropy on thermal conduction were investigated. The measurements were done in longitudinal (parallel to the grain) and transverse (intermediate between radial and tangential) directions. As the temperature increased from 20 to 100 °C, the thermal conductivity of each sample increased slightly for both longitudinal and transverse directions. The effect of density and porosity on the thermal conductivity may be related to the presence of other scattering mechanisms such as voids and cell boundaries. It seems that the dominant mechanism of heat transfer across the cell lumina in these types of wood is the heat conduction through the voids. An attempt was made to explain the behaviour of the effective thermal conductivity by adopting a model based on the ratio between heat conduction in parallel and serial layers of gas, liquid, and solid phases.

Application of the three omega thermal conductivity measurement method to a film on a substrate of finite thickness

Abstract: The three omega thermal conductivity measurement method is analyzed for the case of one or more thin films on a substrate of finite thickness. The analysis is used to obtain the thermal conductivities of SiO2 films on Si substrates and of a chemical vapor deposition (CVD) diamond plate. For the case of the SiO2 films on a Si, we find an apparent thickness dependence of the thermal conductivity of the SiO2 films. However, the data can also be explained by a thickness-independent thermal conductivity and an interfacial thermal resistance. For the case of the CVD diamond plate, the fit of the theory to the experimental data is significantly improved if we assume that an interface layer separates the heater from the diamond plate.

A Study on Thermal Resistance over a Solid-Liquid Interface by the Molecular Dynamics Method *

Abstract: Through molecular dynamics simulations, it was demonstrated that a thermal resistance cannot be neglected over a solid-liquid interface when a system size is very small, i.e. the relative importance of thermal resistance of heat conduction is small. A quasi-steady non-equilibrium heat-transfer simulation was performed with the molecular dynamics method. A vapor region was sandwiched between liquid layers, which were in contact with two solid walls. While independently controlling temperatures at ends of walls by the phantom method, the energy flux through the system was accurately calculated. The measured temperature distribution normal to interfaces showed a distinctive jump near the solid-liquid interface, which could be regarded as the thermal resistance over the interface. The thermal resistance was measured for various interaction potential parameters between solid and liquid molecules so that a wide range of wettability could be covered. The thermal resistance was equivalent to 5~20 nm thickness of liquid heat conduction layer, and was strongly dependent on the wettability.

Observation of proportionality between friction and contact area at the nanometer scale

Abstract: The nanotribological properties of a hydrogen‐terminated diamond(111)/tungsten‐carbide interface have been studied using ultra‐high vacuum atomic force microscopy. Both friction and local contact conductance were measured as a function of applied load. The contact conductance experiments provide a direct and independent way of determining the contact area between the conductive tungsten‐carbide AFM tip and the doped diamond sample. We demonstrate that the friction force is directly proportional to the real area of contact at the nanometer‐scale. Furthermore, the relation between the contact area and load for this extremely hard heterocontact is found to be in excellent agreement with the Derjaguin–Muller–Toporov continuum mechanics model.

DC thermal microscopy: study of the thermal exchange between a probe and a sample

Abstract: The Scanning Thermal Microscopic (SThM) probe, a thin Pt resistance wire, is used in the constant force mode of an Atomic Force Microscope (AFM). Thermal signal-distance curves for differing degrees of relative humidity and different surrounding gases demonstrate how heat is transferred from the heated probe to the sample. It is known that water affects atomic force microscopy and thermal measurements; we report here on the variation of the water interaction on the thermal coupling versus the probe temperature. Measurements were taken for several solid materials and show that the predominant heat transfer mechanisms taking part in thermal coupling are dependent on the thermal conductivity of the sample. The results have important implications for any quantitative interpretation of thermal images made in air.

Measurements of adhesive bondline effective thermal conductivity and thermal resistance using the laser flash method

Abstract: Thermal modeling of device packages requires accurate thermophysical property data for package materials. Accurate data for the thermal resistance of the adhesive bondline used to attach a high power device to a substrate is critical because this thermal resistance can be a significant part of the total thermal resistance in the heat flow path from the device junction to the package case or ambient. The bondline thermal resistance can in principle be calculated by dividing the expected or measured bondline thickness by the adhesive thermal conductivity measured on a free-standing cured sample. However, at a typical bondline thickness of 15-75 /spl mu/m, the contact thermal resistance between the adhesive and its adherents can be significant compared to the intrinsic thermal resistance of the adhesive and thus cannot be ignored. Also, the thermal conductivity measured on a free-standing cured sample may not be equivalent to the thermal conductivity of the adhesive in the bonded assembly. This paper investigates some of the variables that determine adhesive bondline effective thermal conductivity and contact resistance. The results of multilayer laser flash diffusivity measurements are presented for a range of available adhesives in "sandwich" sample assemblies that simulate the package. Thermal conductivity measurements of the free-standing adhesives are also obtained by the laser flash method.

Optical Measurement of Thermal Contact Conductance Between Wafer-Like Thin Solid Samples

Abstract: We present a noncontact optical technique for measuring the thermal contact conductance between wafer-like thin solid samples. The technique is based on heating one solid surface by a modulated laser beam and monitoring the corresponding temperature modulation of the other solid surface across the interface using the reflectance of a probe laser beam. The phase lag between the two laser signals is independent of the optical properties of the samples as well as the laser intensities, and can be related to the thermal contact conductance. A detailed theoretical analysis is presented to estimate the thermal contact conductance as well as the thermophysical properties of the solids from the phase tag measured as a function of the modulation frequency. Closed-form solutions in the high-frequency limit are derived in order to provide a simple estimation procedure. The effect of misalignment of the two lasers is studied and the conditions for robust measurements are suggested. As a benchmark for this technique, the thermal conductivity of a single crystal silicon sample was measured to within two percent of reported values. The thermal contact conductance was measured for Al-Si samples, each about 0.22 mm thick, in the pressure range of 0.8-10 MPa

Thermal conductivity of SiO2 films by scanning thermal microscopy

Abstract: In microelectronics the thermal conductivity of dielectric films such as SiO 2 is of concern because, as dimensions shrink, heat removal from devices becomes a critical problem. A scanning thermal microscope was used to image thermal properties of silicon dioxide films deposited on silicon by plasma enhanced chemical vapor deposition. Thermal conductivity as a function of the layer thickness, ranging 50–1000 nm was measured. To interpret the experimental thermal data, a model has been developed on the basis of previously published heat-transfer concepts. An intrinsic thermal conductivity of 1.31 ± 0.11 W/K/m was calculated independent of the thickness and a thermal resistance of (6.8 ± 0.35) × 10 −7 m 2 K/W was calculated at the interfaces.

A Thermoelastic Asperity Contact Model Considering Steady-State Heat Transfer

Abstract: One of the important issues in mixed lubrication is the contact problem involving frictional heating in the interface of contacting bodies. Due to contact and rubbing, temperature in the solid media varies, causing the contact conditions to change as a consequence of thermal distortion. A thermoelastic model for rough surfaces is developed for asperity contact subject to steady-state heat transfer. In this model, asperity distortion due to thermal and elastic-plastic deformations is considered. The thermal deformation is related to the contact pressure through a thermal influence function. Matrices for thermal and elastic influence functions are solved with the finite element method and the contact problem is computed with a mathematical programming method. Numerical analyses on the thermoelastic contact involving a rough surface reveal that asperity thermal distortion affects the contact pressure and surface separation at high frictional heat and deep asperity penetration. Presented at the 54th Annual Me...

Thermal conduction through a molecule

Abstract: The quantum features of phononic thermal conduction through a molecule between two reservoirs have been studied in the weak-coupling limit. As opposed to ballistic heat transfer through a uniform bridge or atomic chain strongly coupled to reservoirs investigated earlier, thermal conductance in the present case shows a nonlinear temperature dependence that is sensitive to the mode frequencies of the molecule.

Combined conduction and radiation heat transfer in plane-parallel packed beds with variable porosity

Abstract: The primary concern of this study deals with the prediction of thermal performance of packed beds with variable porosity. Combined conduction and radiation heat transfer in plane-parallel packed beds of spherical particles was investigated numerically. The effects of variable porosity, effective thermal conductivity, and thermal radiation were taken into account. The method for radiative transfer equation was based on the P3-spherical harmonic approximation, while the finite-difference scheme was employed to solve the energy equation. Four different models of porosity distributions were tested. It was found that variable porosity and effective thermal conductivity effects on the mean total effective thermal conductivity and radiative heat flux distributions are important and should not be ignored.

Thermoelasticity and contact

Abstract: Thermoelastic deformations can have a significant effect on the contact between elastic bodies, particularly in cases where the thermal boundary conditions at the interface are influenced by the contact pressure. In the classical Hertzian problem, the size of the contact area depends on the magnitude and direction of heat flow between the bodies. Idealized thermal boundary conditions can lead to ill-posed steady-state problems, but this difficulty is resolved by assuming a pressure-dependent thermal contact resistance. Steady states of the system can be unstable even when they are unique, in which case the behavior is either oscillatory or involves the steady motion of a contact pressure wave along the interface. Analytical and numerical perturbation methods have been developed to investigate the stability problem. These results find applications in heat transfer processes involving solid-solid contact, including the solidification of castings. In brakes and clutches, the heat generated at the sliding int...

A new space marching method for solving inverse heat conduction problems

Abstract: A new space marching method is presented for solving the one-dimensional nonlinear inverse heat conduction problems. The temperature-dependent thermal properties and boundary condition on an accessible part of the boundary of the body are known. Additional temperature measurements in time are taken with a sensor located in an arbitrary position within the solid, and the objective is to determine the surface temperature and heat flux on the remaining part of the unspecified boundary. The temperature distribution throughout the solid, obtained from the inverse analysis, is then used for the computation of thermal stresses in the entire domain, including the boundary surfaces. The proposed method is appropriate for on-line monitoring of thermal stresses in pressure components. The three presented example show that the method is stable and accurate.

Determination of the thermal conductivity of foam aluminum

Abstract: We present calculations and experimental data on determination of the thermal conductivity of porous foam aluminum materials. We analyze the possibility of their use for thermal insulation.

Measurement of buried oxide thermal conductivity for accurate electrothermal simulation of SOI device

Abstract: Finite element simulations demonstrate that the thermal conductivity of the buried oxide is an important parameter for the modeling of the thermal behavior of silicon-on insulator (SOI) devices. There is uncertainty about the conductivity of different forms of SiO/sub 2/, particularly that of buried oxides. This paper presents a novel approach to measure this conductivity, using structures that are compatible with standard bipolar or CMOS processes. Thermal conductivity values of 0.66 and 0.82 W/mK, respectively, were found for 300-nm BESOI and 420-nm SIMOX oxides at room temperature. The measured variations of thermal conducitivity with temperature agree well with bulk SiO/sub 2/ behavior. Better agreement between measurement and finite element simulation of MOSFET thermal resistance is obtained by using these extracted thermal conductivity values. It is also shown that the role of the silicon substrate in determining the thermal resistance of the device can be calculated using a simple analytical model. This is important when one wishes to calculate accurately individual thermal resistances of transistors in a given circuit.

Thermal spreading resistance in multilayered contacts : Applications in thermal contact resistance

Abstract: Application of highly conductive coatings to contacting surfaces is a commonly employed method to enhance thermal contact conductance. In many applications it is often necessary to apply an intermediate coating such that the conductive coating may be applied to a nonadhering substrate. In these instances, it is desirable to predict the effect that the intermediate and e nal coatings have on the spreading resistance. A solution for computing the thermalspreading resistanceofa planarcircularcontactona doubly coatedsubstrateispresented.Also,a modelis developed to compute the contact conductance between a bare substrate and a coated substrate. Comparisons are made with data obtained in the literature for which no analytical model was available. Solution of the governing equations and numerical computation of the spreading resistance were obtained using computer algebra systems. Nomenclature Ac; At; Aa = area, m 2 Ain; Bin = Fourier‐Bessel coefe cients a;b = two radii with a < b, m CL = spreading correction factor e = natural log base Hc = contact microhardness, MPa hc = contact conductance, W/m 2 K J0.x/

Thermal spreading resistance in multilayered contacts : Applications in thermal contact resistance

Abstract: Application of highly conductive coatings to contacting surfaces is a commonly employed method to enhance thermal contact conductance. In many applications it is often necessary to apply an intermediate coating such that the conductive coating may be applied to a nonadhering substrate. In these instances, it is desirable to predict the effect that the intermediate and final coatings have on the spreading resistance. A solution for computing the thermal spreading resistance of a planar circular contact on a doubly coated substrate is presented. Also, a model is developed to compute the contact conductance between a bare substrate and a coated substrate. Comparisons are made with data obtained in the literature for which no analytical model was available. Solution of the governing equations and numerical computation of the spreading resistance were obtained using computer algebra systems

Thermal modeling of roll and strip interface in rolling processes: part 2-simulation

Abstract: Part 1 of this paper\[1] reviewed the modeling approaches and correlations used to study the interface heat transfer phenomena of the roll-strip contact region in rolling processes. The thermal contact conductance approach was recommended for modeling the interface phenomena. To illustrate, the recommended approach and selected correlations are adopted in the present study for modeling of the roll-strip interface region. The specific values of the parameters used to correlate the corresponding thermal contact conductance for the typical cold and hot rolling of steels are first estimated. The influence of thermal contact resistance on the temperature distributions of the roll and strip is then studied. Comparing the present simulation results with previously published experimental and analytical results shows that the thermal contact conductance approach and numerical models used can reliably simulate the heat transfer behavior of the rolling process.

Effects of porosity on the thermal properties of a 380-aluminum alloy

Abstract: Effective values of the thermal diffusivity, specific heat, and thermal conductivity of a porous 380-aluminum alloy prepared by melting in a gas-fired furnace, were determined as a function of the volume fraction of porosity. For that, photoacoustic, differential calorimetric, density, and image analyzer measurements were done. Thermal conductivity and specific heat capacity decrease with the increase of porosity, whereas the thermal diffusivity shows less dependence. Among the effective models for analysis of the thermal conductivity of a two-phase system, the Maxwell model best fits the experimental data, implying a homogenous distribution of the pores in the aluminum-alloy matrix.

Influence of Order–Disorder Transition on Thermal Conductivity of Solids

Abstract: The relation between the crystalline structure and thermal properties of solids is analyzed. The brief description of the theories of heat conduction in polycrystalline solids (Callaway model) and amorphous solids (Cahill–Pohl) model is carried out. It is shown that transition from the heat transport by phonons in polycrystals to the random energy transfer between localized oscillators in glasses leads to the meaningful reduction of the thermal conductivity. This conclusion is illustrated by experimental data. The limitations of obtaining thin films with good thermal properties are underlined.

Substrate for heat radiation, and its manufacture

Abstract: PROBLEM TO BE SOLVED: To provide a substrate for heat radiation which is high in coefficient of heat conduction, low in coefficient of thermal expansion and small in thermal strain. SOLUTION: A porous material formed of a thermal expansion suppression material such as SiC powder is arranged in a casting cavity, a molten base material of =400 deg.C and below or equal to the solidification temperature. The thermal stress in an internal layer and a surface layer different in coefficient of thermal expansion from each other, is sufficiently removed, and the alloy composition to be added to improve the fluidity is sufficiently precipitated.

The measurement of thermal conductivities of solid fruits and vegetables

Abstract: A thermal conductivity probe consisting of a heating cell, a thermocouple and a guard tube over the heating cell was developed and is described here. Analyses demonstrate that the guard tube acts as a thermal contact resistance. This resistance does not influence measurements of thermal conductivity significantly, but it must be considered in an accurate measurement of thermal diffusivity, especially when there is a gap between the heater and the guard tube. Calibration of the probe with glycerine in this work exhibits an accuracy of 1.4% for thermal conductivity measurements. The probe was used to measure the thermal conductivities of some solid fruits and vegetables. The sizes of both specimen and probe were analysed and their influences controlled to be under 1.0%. Each measurement was completed within two minutes and the temperature rise was less than under 6 °C. The water content of fruits and vegetables was found to be the dominant factor in determining their thermal conductivities. An empirical relationship between thermal conductivity and mass density is proposed based on the measurements. It is shown that this relation gives a deviation from experimental data of only 11%.