Showing papers on "Thermal diffusivity published in 2005"

Measurement of thermo-optic properties of Y3Al5O12, Lu3Al5O12, YAIO3, LiYF4, LiLuF4, BaY2F8, KGd(WO4)2, and KY(WO4)2 laser crystals in the 80–300K temperature range

Abstract: Thermo-optic materials properties of laser host materials have been measured to enable solid-state laser performance modeling The thermo-optic properties include thermal diffusivity (β), specific heat at constant pressure (Cp), thermal conductivity (κ), coefficient of thermal expansion (α), thermal coefficient of the optical path length (γ) equal to (dO∕dT)∕L, and thermal coefficient of refractive index (dn∕dT) at 1064nm; O denotes the optical path length, which is equal to the product of the refractive index (n) and sample length (L) Thermal diffusivity and specific heat were measured using laser-flash method Thermal conductivity was deduced using measured values of β, Cp, and the density (ρ) Thermal expansion was measured using a Michelson laser interferometer Thermal coefficient of the optical path length was measured at 1064nm, using interference between light reflected from the front and rear facets of the sample Thermal coefficient of the refractive index was determined, using the measured val

Surgical sealing surfaces and methods of use

Abstract: Various embodiments provide compositions that exhibit positive temperature coefficient of resistance (PTCR) properties for use in thermal interactions with tissue—including thermal sensing and I2R current-limiting interactions. Embodiments also provide tissue-engaging surfaces having PTCR materials that provide very fast switching times between low resistance and high, current-limiting resistance. One embodiment provides a matrix for an electrosurgical energy delivery surface comprising a PTCR material and a heat exchange material disposed within an interior of the matrix. The PTCR material has a substantially conductive state and a substantially non-conductive state. The heat exchange material has a structure configured to have an omni-directional thermal diffusivity for exchanging heat with the PTCR material to cause rapid switching of the PTCR material between the conductive state and non-conductive state. Preferably, the structure comprises a graphite foam having an open cell configuration. The matrix can be carried by tissue contacting surfaces of various electrosurgical devices.

Diffusivities of Gases in Room-Temperature Ionic Liquids: Data and Correlations Obtained Using a Lag-Time Technique

Abstract: Diffusivity and solubility data are presented for carbon dioxide, ethylene, propylene, 1-butene, and 1,3-butadiene in five imidazolium-based ionic liquids and one phosphonium-based ionic liquid covering a liquid viscosity range of 10−1000 cP. The data were obtained using a lag-time technique that involves analysis of both the transient and steady-state permeation regimes through a supported liquid film. In general, gas diffusion in ionic liquids (∼10-6 cm2/sec) is slower than that in traditional hydrocarbon solvents and water, but the dependence on viscosity is lower. Conversely, the dependence of diffusivity on temperature and the size of the solute gas is higher than that for nonpolar solvents. A correlation for gas diffusivity in ionic liquids at 30 °C is proposed in terms of the gas molar volume, the ionic liquid viscosity, and density, based on 30 data points with a coefficient of multiple determination r2 = 0.975.

Properties of group-IV, III-V and II-VI semiconductors

Abstract: Series Preface. Preface. Acknowledgements. 1 Structural Properties. 1.1 Ionicity. 1.2 Elemental Isotopic Abundance and Molecular Weight. 1.3 Crystal Structure and Space Group. 1.4 Lattice Constant and Its Related Parameters. 1.5 Structural Phase Transition. 1.6 Cleavage Plane. 2 Thermal Properties. 2.1 Melting Point and Its Related Parameters. 2.2 Specific Heat. 2.3 Debye Temperature. 2.4 Thermal Expansion Coefficient. 2.5 Thermal Conductivity and Diffusivity. 3 Elastic Properties. 3.1 Elastic Constant. 3.2 Third-Order Elastic Constant. 3.3 Young's Modulus, Poisson's Ratio and Similar. 3.4 Microhardness. 3.5 Sound Velocity. 4 Lattice Dynamic Properties. 4.1 Phonon Dispersion Relation. 4.2 Phonon Frequency. 4.3 Mode Gruneisen Parameter. 4.4 Phonon Deformation Potential. 5 Collective Effects and Some Response Characteristics. 5.1 Piezoelectric and Electromechanical Constants. 5.2 Frohlich Coupling Constant. 6 Energy-Band Structure: Energy-Band Gaps. 6.1 Basic Properties. 6.2 E0-Gap Region. 6.3 Higher-Lying Direct Gap. 6.4 Lowest Indirect Gap. 6.5 Conduction-Valley Energy Separation. 6.6 Direct-Indirect-Gap Transition Pressure. 7 Energy-Band Structure: Effective Masses. 7.1 Electron Effective Mass: G Valley. 7.2 Electron Effective Mass: Satellite Valley. 7.3 Hole Effective Mass. 8 Deformation Potentials. 8.1 Intravalley Deformation Potential: G Point. 8.2 Intravalley Deformation Potential: High-Symmetry Points. 8.3 Intervalley Deformation Potential. 9 Electron Affinity and Schottky Barrier Height. 9.1 Electron Affinity. 9.2 Schottky Barrier Height. 10 Optical Properties. 10.1 Summary of Optical Dispersion Relations. 10.2 The Reststrahlen Region. 10.3 At or Near The Fundamental Absorption Edge. 10.4 The Interband Transition Region. 10.5 Free-Carrier Absorption and Related Phenomena. 11 Elastooptic, Electrooptic and Nonlinear Optical Properties 11.1 Elastooptic Effect. 11.2 Linear Electrooptic Constant. 11.3 Quadratic Electrooptic Constant. 11.4 Franz-Keldysh Effect. 11.5 Nonlinear Optical Constant. 12 Carrier Transport Properties. 12.1 Low-Field Mobility: Electrons. 12.2 Low-Field Mobility: Holes. 12.3 High-Field Transport: Electrons. 12.4 High-Field Transport: Holes. 12.5 Minority-Carrier Transport: Electrons in p-Type Materials. 12.6 Minority-Carrier Transport: Holes in n-Type Materials. 12.7 Impact Ionization Coefficient. Index.

Electrical and thermal behavior of polypropylene filled with copper particles

Abstract: Thermal conductivity, diffusivity, effusivity and specific heat of polypropylene matrix filled with copper particles of two different sizes were investigated. A parallel study of the evolution of the electrical conductivity was also carried out. The highest heat transport ability was observed for the composites filled with the smaller particles. Electrical conductivity investigations showed that the size of fillers also influences the percolation threshold. The Agari's model provides a good estimation of the thermal conductivity of composites for all filler concentrations. It was used in order to give a comparative analysis of both electrical and thermal properties of such two-phase systems. Nevertheless, the physical meaning of the two fitting parameters C1 and C2 of Agari's model has to be completed.

Molecular dynamics simulations of polymer transport in nanocomposites.

Abstract: Molecular dynamics simulations on the Kremer-Grest bead-spring model of polymer melts are used to study the effect of spherical nanoparticles on chain diffusion. We find that chain diffusivity is enhanced relative to its bulk value when polymer-particle interactions are repulsive and is reduced when polymer-particle interactions are strongly attractive. In both cases chain diffusivity assumes its bulk value when the chain center of mass is about one radius of gyration R(g) away from the particle surface. This behavior echoes the behavior of polymer melts confined between two flat surfaces, except in the limit of severe confinement where the surface influence on polymer mobility is more pronounced for flat surfaces. A particularly interesting fact is that, even though chain motion is strongly speeded up in the presence of repulsive boundaries, this effect can be reversed by pinning one isolated monomer onto the surface. This result strongly stresses the importance of properly specifying boundary conditions when the near surface dynamics of chains are studied.

Simulation of Nanoscale Multidimensional Transient Heat Conduction Problems Using Ballistic-Diffusive Equations and Phonon Boltzmann Equation

Abstract: Heat conduction. in micro- and nanoscale and in ultrafast processes may deviate from the predictions of the Fourier law, due to boundary and interface scattering, the ballistic nature of the transport, and the finite relaxation time of heat carriers. The transient ballistic-diffusive heat conduction equations (BDE) were developed as an approximation to the phonon Boltzmann equation (BTE) for nanoscale heat conduction problems. In this paper, we further develop BDE for multidimensional heat conduction, including nanoscale heat source term and different boundary conditions, and compare the simulation results with those obtained from the phonon BTE and the Fourier law. The numerical solution strategies for multidimensional nanoscale heat conduction using BDE are presented. Several two-dimensional cases are simulated and compared to the results of the transient phonon BTE and the Fourier heat conduction theory. The transient BTE is solved using the discrete ordinates method with a two Gauss-Legendre quadratures. Special attention has been paid to the boundary conditions. Compared to the cases without internal heat generation, the difference between the BTE and BDE is larger for the case studied with internal heat generation due to the nature of the ballistic-diffusive approximation, but the results from BDE are still significantly better than those from the Fourier law. Thus we conclude that BDE captures the characteristics of the phonon BTE with much shorter computational time.

Oxygen Diffusion in Yttria-Stabilized Zirconia: A New Simulation Model

Abstract: We present a multiscale modeling approach to study oxygen diffusion in cubic yttria-stabilized zirconia. In this approach, we employ density functional theory methods to calculate activation energies for oxygen migration in different cation environments. These are used in a kinetic Monte Carlo framework to calculate long-time oxygen diffusivities. Simulation results show that the oxygen diffusivity attains a maximum value at around 0.1 mole fraction yttria. This variation in the oxygen diffusivity with yttria mole fraction and the calculated values for the diffusivity agree well with experiment. The competing effects of increased oxygen vacancy concentration and increasing activation energy and correlation effects for oxygen diffusion with increasing yttria mole fraction are responsible for the observed dopant content dependence of the oxygen diffusivity. We provide a detailed analysis of cation-dopant-induced correlation effects in support of the above explanation.

A hydrodynamic shear instability in stratified disks

Abstract: We discuss the possibility that astrophysical accretion disks are dynamically unstable to non-axisymmetric distur- bances with characteristic scales much smaller than the vertical scale height. The instability is studied using three methods: one based on the energy integral, which allows the determination of a sufficient condition of stability, one using a WKB approach, which allows the determination of the necessary and sufficient condition for instability and a last one by numerical solution. This linear instability occurs in any inviscid stably stratified differential rotating fluid for rigid, stress-free or periodic boundary conditions, provided the angular velocity Ω decreases outwards with radius r. At not too small stratification, its growth rate is a fraction of Ω. The influence of viscous dissipation and thermal diffusivity on the instability is studied numerically, with emphasis on the case when d ln Ω/ dl nr = −3/2 (Keplerian case). Strong stratification and large diffusivity are found to have a stabilizing effect. The corresponding critical stratification and Reynolds number for the onset of the instability in a typical disk are derived. We propose that the spontaneous generation of these linear modes is the source of turbulence in disks, especially in weakly ionized disks.

New Measurement of Thermal Properties of Superpave Asphalt Concrete

Abstract: Reliable implementation of transient temperature prediction models for asphalt pavements has been impeded by lack of reliable thermo–physical properties data. The existing methodology based on ASTM C177-85 is not conducive to asphalt concrete specimens due to the difficulty to meet the slab requirements of the standard. This paper discusses a new laboratory procedure for the determination of thermal properties of asphalt concrete specimens. The new device can accommodate small specimens derived from either laboratory compacted 150 mm diameter briquettes or cores from in-service pavements. The effect of compaction on thermal properties was tested by compacting the briquettes to 67, 99, 133, and 212 gyrations using the superpave gyratory compactor. Thermal conductivity (λ) was determined after the experiment reached steady state, whereas thermal diffusivity (α) was determined during the transient state. Analytical curve fitting technique was applied to the test data to compute the thermal diffusivity. Therm...

Photopyroelectric measurement of thermal conductivity of metallic powders

Abstract: The effective thermal diffusivity of metal powders in air at room temperature is measured by the photopyroelectric technique. The thermal conductivity is calculated from the diffusivity, the relative density, and the specific heat obtained from literature. Maxwell’s model is a good prediction but underestimates the measured effective thermal conductivity, especially for irregular particles. Due to the large difference between the thermal conductivity of metals and air, the effective conductivity is mainly determined by the relative density of the powder bed but not by the properties of the powder material. A theoretical model showing the influence of grain size and gas pressure is presented. The dependence on the particles’ size and pressure is explained by the gradual transition from the free molecular to conductive mechanism of heat transfer in gaps between particles. The theory gives a precise estimation of effective thermal conductivity for metallic powders with a narrow size distribution of spherical...

Development of Graphical Methods for Estimating the Diffusivity Coefficient of Gases in Bitumen from Pressure-Decay Data

Abstract: New graphical techniques are presented for estimating the diffusivity coefficient (or mass diffusivity) of CO2 ,C H 4, and N2 in highly viscous bitumens from pressure-decay data. These methods are based on modeling the rate of change in system pressure as gas diffuses into the bitumen using the diffusion equation, coupled with a mass balance for the gas phase. Analytical solutions of the resulting set of equations, with appropriate initial and boundary conditions, are obtained by Laplace transformation. An inverse solution technique is used for developing two graphical methods to estimate the diffusivity coefficient from pressure-decay data reported in the literature. The estimated diffusivity coefficients for gas-bitumen pairs at 75-90 °C vary from 2.5 10 -10 m 2 /s to 7.8 10 -10 m 2 /s, and these are in good agreement with literature values. The novelty of the proposed methodology is in its simplicity and its ability to isolate portions of the pressure-decay data that are affected by experimental fluctuations. This enables the consideration of only that portion of the data that is consistent with the analytical solution.

Thermal response of sediment with vertical fluid flow to periodic temperature variation at the surface

Abstract: [1] Characteristics of thermal responses of sediment with vertical fluid movement to periodic temperature variation at the surface were examined using a one-dimensional analytical solution. The amplitude of the thermal response decays exponentially, and the phase is delayed linearly with increasing depth, but they depend on the direction and velocity of vertical fluid flow, thermal diffusivity of fluid-saturated sediment, and period of surface temperature variation. To examine general characteristics of the thermal response, we defined two nondimensional parameters related to thermal diffusivity of fluid-saturated sediment, vertical fluid flow velocity, period of the surface temperature variation, and specific penetration depth at which the amplitude of the thermal response decays to e−1 of that at the surface. Analysis using these nondimensional parameters shows that there are three heat transport regimes for downward flow: (1) heat transport strongly governed by advection, (2) heat transport strongly governed by conduction, and (3) transition between these regimes. For upward flow, there are also three heat transport regimes: (1) balance of heat transports by advection and conduction, (2) heat transport strongly governed by conduction, and (3) transition between these regimes. The analytical solution is used to estimate the downward fluid velocity and thermal diffusivity of sediment from temperatures measured by long-term temperature monitoring at a site of seafloor hydrothermal circulation.

Nonstationary nonlinear effects in optical microspheres

Abstract: Thermal nonlinearity can produce oscillatory instability in optical microspheres. We experimentally demonstrate this instability and analyze the conditions needed to observe this regime. The observed behavior is in good agreement with the results of numerical simulation. In pure fused silica with low optical absorption the thermal oscillations are suppressed owing to an interaction of thermal and Kerr nonlinearities. We also describe experimentally observed slow and irreversible thermo-optical processes in microspheres.

Effect of Fe Segregation on the Migration of a Non-Symmetric Σ5 Tilt Grain Boundary in Al

Abstract: We present an analysis, based upon atomistic simulation data, of the effect of Fe impurities on grain boundary migration in Al. The first step is the development of a new interatomic potential for Fe in Al. This potential provides an accurate description of Al–Fe liquid diffraction data and the bulk diffusivity of Fe in Al. We use this potential to determine the physical parameters in the Cahn–Lucke–Stuwe (CLS) model for the effect of impurities on grain boundary mobility. These include the heat of segregation of Fe to grain boundaries in Al and the diffusivity of Fe in Al. Using the simulation-parameterized CLS model, we predict the grain boundary mobility in Al in the presence of Fe as a function of temperature and Fe concentration. The order of magnitude and the trends in the mobility from the simulations are in agreement with existing experimental results.

Variation of surface albedo and soil thermal parameters with soil moisture content at a semi-desert site on the western Tibetan Plateau

Abstract: Almost three years of continuous measurements taken between January 2001 and May 2003 at the Gaize (or Gerze) automatic weather station (32.30N, 84.06E, 4420 m), a cold semi-desert site on the western Tibetan Plateau, have been used to study seasonal and annual variations of surface albedo and soil thermal parameters, such as thermal conductivity, thermal capacity and thermal diffusivity, and their relationship to soil moisture content. Most of these parameters undergo dramatic seasonal and annual variations. Surface albedo decreases with increasing soil moisture content, showing the typical exponential relation between surface albedo and soil moisture. Soil thermal conductivity increases as a power function of soil moisture content. The diffusivity first increases with increasing soil moisture, reaching its maximum at about 0.25 (volume per volume), then slowly decreases. Soil thermal capacity is rather stable for a wide range of soil moisture content.

Evaluating thermal response tests using parameter estimation for thermal conductivity and thermal capacity

Abstract: Thermal response tests (TRT) record the temperature variation of closed-loop shallow borehole heat exchangers (BHE) due to fluid circulation. The average change of fluid temperature is directly related to the rock thermal conductivity λ around the well. If environmental and experimental conditions satisfy the usual experimental standards, TRT can predict effective ground thermal conductivity within an error of approximately ±10%. This accuracy is generally accepted as sufficient for an appropriate prediction of the geothermal heat yield. However, the line source approach (on which the analysis of the TRT experiment is based) does not allow us to derive thermal capacity independently from thermal conductivity, and the soil thermal capacity ρc is usually assumed constant here. We calculate the response temperature of a synthetic TRT experiment as a reference for a subsequent joint estimation of rock thermal conductivity and thermal capacity. Within a reasonable computing time, a comprehensive parameter estimation is impossible, if coupled fluid flow and heat transport in the BHE tubes are explicitly simulated. Therefore, we substitute the BHE tube by a constant heat source with diffusive heat transport only. Although this simplification limits the application of the method to synthetic TRT data, we perform a systematic study of the method's accuracy to analyse thermal capacity with respect to data noise and test duration. Finding the minimum misfit with respect to the reference experiment, we obtain both thermal conductivity and thermal capacity, i.e. more information on ground thermal properties than the line source theory can provide. The effect of the additional information on the ground thermal capacity is demonstrated by a numerical simulation of a real TRT, where the fluid flow and the heat transport within the BHE tube are explicitly simulated. Nevertheless, thermal capacity is generally variable within ±20% for the same rock type. In our analysis, this uncertainty results in a variation of ±2% of the outlet temperature.