Showing papers on "Thermal diffusivity published in 1988"

Solubility and Diffusivity of Acid Gases (CO2, N2O) in Aqueous Alkanolamine Solutions

Abstract: Solubility and diffusivity of N2O and CO2 in water were determined as a function of temperature from the results published in the open literature, and new data were measured in the present work. The solubility of N2O in several aqueous alkanolamine (DEA, DIPA, DMMEA, and DIPA) solutions at various temperatures was measured and correlated over a wide range of conditions. For both the diffusivity of N2O and the alkanolamine in aqueous alkanolamine solutions a modified Stokes-Einstein relation was derived. With the aid also of the “N2O analogy” the diffusivity of CO2 in these solutions can be estimated.

Thermal properties of rocks

Abstract: All the important thermal properties of rocks can be estimated from the graphs and tables in this report. Most of the useful published data are summarized herein to provide fairly accurate evaluations of thermal coefficients and parameters of rocks for many engineering and scientific purposes. Graphs of the published data on common rocks and minerals were prepared to show the relationships of thermal conductivity with decimal solidity (one minus decimal porosity), water or air pore content, content of certain highly conducting minerals, and temperature. Tables are given of pressure effect on thermal conductivity of minerals and rocks, anisotropy of conductivity, thermal expansion, heat transfer, density, heat generation in rocks, and activation energies of conduction mechanisms in single crystals of minerals. A series of graphs show the specific heats of rock-forming minerals as a function of temperature; with these graphs the specific heat of a rock can be calculated from its mode as accurately as it can be measured. Calculations of conductivity, diffusivity, and thermal inertia of a rock from its mode are described. Discussions of radiative thermal conductivity, radioactive heat generation, and heat transfer in rocks are provided.

The mechanics of spin coating of polymer films

Abstract: The process of spin coating is described, with particular attention to applications in microelectronics. The physical mechanisms involved in the process are discussed and those mechanisms that affect the final state are identified, viz., centrifugal and viscous forces, solute diffusion, and solvent evaporation: A model is proposed that incorporates only the latter mechanisms, with viscosity and diffusivity depending on solute concentration. The evaporation of solvent during spinning causes the solution viscosity to increase and the flow is reduced. The thickness of the final solid film is related to the thickness of a diffusion boundary layer near the free surface. The model predicts the final dry film thickness in terms of the primary process variables, spin speed, and initial polymer concentration. A similarity boundary‐layer analysis leads to a simple approximate result for the final film thickness that is consistent with limited experimental data, hf ∼KC0(ν0D0)1/4/Ω1/2, where K is a number of order un...

A Two-Equation Model for Heat Transport in Wall Turbulent Shear Flows

Abstract: A new proposal for closing the energy equation is presented at the two-equation level of turbulence modeling. The eddy diffusivity concept is used in modeling. However, just as the eddy viscosity is determined from solutions of the k and {var epsilon} equations, so they eddy diffusivity for heat is given as functions of temperature variance t{sup 2}, and the dissipation rate of temperature fluctuations {var epsilon}{sub t}, together wtih k and {var epsilon}. Thus, the proposed model does not require any questionable assumptions for the turbulent Prandtl number. Modeled forms of the t{sup 2} and {var epsilon} equations are developed to account for the physical effects of molecular Prandtl number and near-wall turbulence. The model is tested by application to a flat-plate boundary layer, the thermal entrance region of a pipe, and the turbulent heat transfer in fluids over a wide range of the Prandtl number. Agreement with the experiment is generally very satisfactory.

Gas diffusion, fluid flow and derived pore continuity indices in relation to vehicle traffic and tillage

Abstract: SUMMARY Relative gas diffusivity, air permeability and hydraulic conductivity were measured in undisturbed soil cores from tillage and traffic experiments Continuity indices were taken as the quotient of relative diffusivity and air-filled porosity, and of air permeability and air-filled porosity (and the square of air-filled porosity) These were applied to individual measurements or to treatment means More general continuity indices were derived from the changes in flow or diffusion with porosity, where the variations in porosity were due to both field variability and applied changes of water potential These indices were the exponent in the relationship between relative diffusivity and air-filled porosity and the slope of log–log plots of air permeability and air-filled porosity or hydraulic conductivity and degree of saturation Some physical significance was attached to the exponents by comparison with models of soil porosity Positive intercepts of the relative diffusivity or air permeability plots on the air-filled porosity axes were taken as porosities blocked to gas movement Continuity indices and flow measurements showed differences between tillage and traffic treatments which did not necessarily reflect differences in bulk density Intrinsic permeability was better estimated from air permeability than from unsaturated hydraulic conductivity

Determination of fluid flow properties from the response of water levels in wells to atmospheric loading

Abstract: The water level in a well that taps a partially confined aquifer is often sensitive to atmospheric loading. The magnitude and character of this response is partly governed by the well radius, the lateral hydraulic diffusivity of the aquifer, the thickness and vertical pneumatic diffusivity of the unsaturated zone, and the thickness and vertical hydraulic diffusivity of the saturated zone overlying the aquifer. These key elements can be combined into five dimensionless parameters that partly govern the phase and attenuation of the response. In many cases, the response of a well to atmospheric loading can be broken up into a high-, intermediate-, and low-frequency response. The high-frequency response is governed largely by the well radius and lateral diffusivity of the aquifer. The intermediate-frequency response is governed by the loading efficiency of the aquifer. The low-frequency response is governed by the vertical pneumatic diffusivity and thickness of the unsaturated zone and the vertical hydraulic diffusivity and thickness of the saturated material above the aquifer. Cross-spectral estimation is used to fit the response to atmospheric loading of three water wells to the theoretical curves in order to yield estimates of three of the key dimensionless parameters. These estimates then are used to make estimates or place bounds on the vertical pneumatic diffusivity of the unsaturated zone, the lateral permeability of the aquifer, and the composite vertical hydraulic diffusivity of the overlying saturated materials.

Transport properties of liquid metals and viscosity of the Earth's core

Abstract: SUMMARY Coefficients expressing transport properties of liquid metals (viscosity and diffusivity) can be scaled to the absolute melting temperature. A systematic review of the published experimental data leads to the conclusion that the effect of pressure on viscosity and diffusivity can be taken into account through its effect on the melting temperature. Hence, the viscosity and diffusivity at the melting temperature are constants for a given metal. The viscosity of the Earth’s liquid core, near the inner core boundary, is probably close to that of liquid iron at ambient pressure, namely 6 CP (centipoises). The viscosity profile in the fluid core has been calculated. Using the same approach for the effect of impurities, it is suggested that the diffusivity of sulphur in the core is probably of the order of

Thermal conductivity of binary, ternary, and quaternary III‐V compounds

Abstract: The room‐temperature thermal conductivity of III‐V compounds is analyzed. The phenomenological approach of Abeles is applied to take into account disordered structure of ternary and quaternary alloys. The procedure is used for the In1−xGaxAsyP1−y quaternary alloy. The approximate analytical expression for this case is derived. A more exact method of the calculations is also proposed. It enables presenting the thermal conductivity and the thermal diffusivity for both the InP lattice‐matched and GaAs lattice‐matched In1−xGaxAsyP1−y alloys as a function of their composition.

Momentum and thermal transport in neutral‐beam‐heated tokamaks

Abstract: The relation between momentum and thermal transport in neutral‐beam‐heated tokamaks with subsonic toroidal rotation velocity has been investigated. A theory of diffusive momentum transport driven by ion‐temperature‐gradient‐driven turbulence (ηi turbulence) is presented. In addition, the level of ηi turbulence is enhanced by radially sheared toroidal rotation. The resulting ion shear viscosity is χφ=1.3{(1+ηi)/τ+[(Ln/2cs) (dV0/dr)]2}2(ρ2scs/ Ls). The associated ion thermal diffusivity, χi, is identical to χφ. Thus a scenario based on velocity‐shear‐enhanced ηi turbulence is consistent with the experimentally observed relationship between thermal and momentum confinement.

A Comparison of Gas Diffusivity Models for Unsaturated Porous Media

Abstract: The effective gas diffusivity in a porous medium decreases rapidly with increasing water content Comparisons are made between experimental diffusivity data for different materials at various moisture contents, and estimation methods from the literature The estimation methods proposed by RJ Millington and RC Shearer in 1971 give the best predictions of the effective diffusivity The methods are extended here to account for the contribution of diffusion in the water-filled pores The method for aggregated media should be used for undisturbed clayey soils, and the method for nonaggregated media may be used for sandy soils and for other materials that are not aggregated, eg laboratory packed clayey soils The experimental data show that very low effective diffusivities may be obtained in practice in soils with high moisture content

Ion collection by probes in strong magnetic fields with plasma flow.

Abstract: Fluid-theory calculations are presented of ion collection by electric probes in strongly magnetized plasmas with parallel flow In the first calculations the problem is treated in a one-dimensional approximation but the cross-field transport of momentum is included in such a way as to model different ratios of viscosity to diffusivity The results show that the flow deduced from probe measurements is not particularly sensitive to the assumed viscosity, provided it is finite However, results with zero viscosity are qualitatively different from those with nonzero viscous momentum transport The second set of calculations is two dimensional but only for fixed (unity) ratio of viscosity to diffusivity The results are in remarkably good agreement with the corresponding one-dimensional model

Crossover from singular to regular behavior of the transport properties of fluids in the critical region.

Abstract: We present a solution of the mode-coupling equations for the dynamics of critical fluctuations which incorporates the crossover from the singular behavior of the transport properties of fluids asymptotically close to the critical point to the regular behavior of these properties far away from the critical point. Good agreement is obtained with experimental thermal diffusivity, thermal conductivity, and viscosity data for carbon dioxide at all temperatures and pressures where critical effects in these transport properties are observed.

Low-Temperature Ion Beam Mixing in Metals

Abstract: A systematic study of ion-beam mixing of tracer impurities in thin metal films at low temperatures has been conducted. We have investigated the dependence of ion mixing on two matrix properties: atomic mass and cohesive energy. We have also studied the dependence of ion mixing on tracer impurity properties: its heat of mixing with the matrix and its thermal diffusivity in the matrix. The matrices investigated were thin films of C, Al, Ti, Fe, Ni, Cu, Mo, Ru, Ag, Hf, Ta, W, Pt, and Au. The tracer impurities, Al, Ti, Cr, Mn, Fe, Ni, Cu, Y, Nb, Mo, Ru, Ag, In, Sb, Hf, Ta, W, Pt, Au, and Bi, were deposited as ≤15 A layers near the midplanes of the specimens. All the tracer and matrix elements, except C, were deposited sequentially, without breaking vacuum. The samples were irradiated with 300–1000-keV Kr ions to doses 1015–1016 ions/cm2 at temperatures of 6 and/or 77 K. Most samples were analyzed at the irradiation temperature by He backscattering. A strong correlation between ion mixing and the matrix properties, atomic mass, and cohesive energy, was observed. A correlation between ion mixing and tracer impurity diffusion was also observed but not between ion mixing and the heat of mixing or relative mass of the impurity with the matrix. The results are interpreted within the framework of a thermal spike model of cascade diffusion.

Non-Darcian Convection in Cylindrical Packed Beds

Abstract: Non-Darcian transport describes the nonuniform flow and thermal anomaliesoften found in flow through packed beds These effects include the high-flow-rate inertial pressure loss, near-wall porosity variation, solid-boundary shear, and thermal dispersion Inclusion of these effects significantly alters the velocity and temperature profiles from those predicted by models using uniform or Darcian flow In this paper, the non-Darcian formulation is used to predict the heat transfer rates for cylindrical packed beds such as chemical reactors Traditional analyses of chemical reactors assume slug flow and must include a temperature-slip boundary condition to predict the measured temperature profiles The present analysis predicts similar temperature variations by allowing the velocity and diffusivity to vary across the bed The results agree with experimental relations needed in conventional reactor models

A Primer of Diffusion Problems

Abstract: Partial table of contents: THE DIFFUSION EQUATION. Isotropic One-dimensional Random Walk. Elementary Properties of the Diffusion Equation. Higher Dimensions and Coordinate Systems. STEADY STATE EXAMPLES. The Steady State is Not the Equilibrium State. The Thermal Oxidation of Silicon. The Precipitation of Spherical Particles. DIFFUSION UNDER EXTERNAL FORCES. One-dimensional Anisotropic Random Walk. Diffusivity and Mobility Coefficients. An Introduction to Double-layers. SIMPLE TIME-DEPENDENT EXAMPLES. The Gaussian and One of Its Relatives. Two Applications of Error Functions to One-dimensional Phases. Crystal Growth under Conditions of Constant Cooling Rate. AN INTRODUCTION TO SIMILARITY. Boltzmann's Transformation. Boltzmann's Transformation and Variable Diffusivity. Analytic Solutions for Variable Diffusivity. A USER'S GUIDE TO THE LAPLACE TRANSFORM. Elementary Properties and Further Examples. The Convolution Theorem. A Few Words on Asymptotics. FURTHER TIME-DEPENDENT EXAMPLES. Laser Processing. Thermally Stimulated Diffusion. Application to the Numerical Solution for Nonlinear Surface Conditions. Appendix A: Random Walks in Higher Dimensions. Appendix B: The Phase Rule and Some of Its Consequences. Appendix C: Moments of Distributions and Asymptotic Behavior. Index.

Thermal properties of wood and wood panel products for use in buildings

Abstract: This report provides a review and evaluation of currently available information on the thermal conductivity and specific heat of wood building materials. We derived a linear equation for thermal conductivity of solid wood as a function of density and moisture content from data in the literature and used this to provide estimated conductivity values for various types of hardwoods and softwoods. Far fewer data exist for the thermal conductivity of wood panel products. Current design values appear to be based on the premise that the conductivity of plywood is the same as that of solid wood of the same species, but the few reported results from the measurements indicate a lower conductivity. More definite information exists on the conductivity of conventional particleboard and fiberboard, but additional conductivity measurements of plywood and some of the most commonly used flakeboards, such as oriented strandboard (OSB), are needed. Additional measurements of the specific heat are needed for all wood panel products. We discuss the special problems of measuring thermal properties of wood products with high moisture contents and the practical relevance of such data to building design and performance, and we conclude that thermal properties above fiber saturation are of little practical significance.more » The report contains the authors' recommendations for design values for thermal properties and for further research and additional measurements, as well as a bibliography. 33 refs., 14 figs., 10 tabs.« less

Time-resolved thermal transport in compositionally modulated metal films.

Abstract: We report on investigations of one-dimensional thermal transport in compositionally modulated metal films produced with a systematic variation in atomic lattice mismatch. In the case of Ni-Cu, Ni-Mo, Ni-Ti, and Ni-Zr, we observe the relative effects of interfacial disorder on thermal diffusion. Our observations demonstrate the thermal impedance of a single metal-metal interface and indicate that thermal diffusion in a bilayer film is strongly influenced by the interface between contacting metal pairs. This study is made possible by picosecond time-resolved thermoreflectance measurements which probe thermal transport perpendicular to the film plane. This technique can impact on our understanding of electron scattering and transport across metallic boundaries, and it provides a means of inferring electrical transport properties.

Gyrokinetic particle simulation of ion temperature gradient drift instabilities

Abstract: Ion temperature gradient drift instabilities have been investigated using gyrokinetic particle simulation techniques for the purpose of identifying the mechanisms responsible for their nonlinear saturation as well as the associated anomalous transport. For simplicity, the simulation has been carried out in a shear‐free slab geometry, where the background pressure gradient is held fixed in time to represent quasistatic profiles typical of tokamak discharges. It is found that the nonlinearly generated zero‐frequency responses for the ion parallel momentum and pressure are the dominant mechanisms giving rise to saturation. This is supported by the excellent agreement between the simulation results and those obtained from mode‐coupling calculations, which give the saturation amplitude as ‖eΦ/Te‖ ≂(‖ωl+iγl‖/Ωi)/(k⊥ ρs)2, and the quasilinear thermal diffusivity as χi ≂γl/k2⊥, where ωl and γl are the linear frequency and growth rate, respectively, for the most unstable mode of the system. In the simulation, the time evolution of χi after saturation is characterized by its slow relaxation to a much lower level of thermal conduction. On the other hand, a small amount of electron–ion collisions, which has a negligible effect on the linear stability, can cause significant enhancement of χi in the steady state.

Real‐time observations of hydrogen drift and diffusion in silicon

Abstract: Real‐time detection of hydrogen motion and bonding has been accomplished by capacitance voltage profiling of various Schottky and metal‐ insulator‐semiconductor capacitors during low‐energy H ion beam injection into the barrier metallization. Finite element analysis modeling of the data indicates that a significant fraction of H interstitials are positively charged, and that bonding of these species with charged boron acceptors proceeds with the large cross section expected of a Coulomb capture process. The 300 K value of the H diffusivity is ≂10−10 cm2/s in agreement with extrapolation of high‐temperature diffusivity data.

Sample overloading effects in polymer characterization by field‐flow fractionation

Abstract: There are two subtechniques of field-flow fractionation (FFF), thermal FFF and flow FFF, that have been successfully employed for polymer fractionation and characterization. These techniques are primarily analytical in nature, yielding accurate polymer characteristics from small sample loads (∼ 10 μg or less, depending on detection sensitivity). In this study the effects of increasing sample size are examined. Modest increases in load are found to result in shifts toward higher retention volumes. These modest loads also result in some broadening of the sample peaks without a major loss of peak symmetry. Excessive loading, by contrast, appears to give rise both to skewed peaks and to new artifact peaks at higher levels of retention. These observations are discussed in terms of the concentration dependence of various properties (viscosity, diffusivity, thermal diffusivity) which influence polymer transport through the FFF channel. The results are used to indicate upper limits to suitable sample concentrations.

Titanium diffusion in silicon

Abstract: Titanium diffusion profiles in silicon were determined in the 950–1200 °C temperature range, with experimental conditions avoiding any oxygen or nitrogen contamination, which could perturb the boundary condition at the TiSi2/Si interface. Thus diffusivity values in the range 5×10−10–10−8 cm2 s−1 are obtained, and are about two orders of magnitude higher than previously reported.

Analysis of combined buoyancy effects of thermal and mass diffusion on laminar forced convection heat transfer in a vertical tube

Abstract: This study investigates the role of vaporization of a thin liquid film onthe tube wall in laminar mixed convection flows under the combined buoyancy effects of thermal and mass diffusion. Results are specifically presented for an air-water system under various conditions. The effects of the liquid film temperature, the Reynolds number, and the relative humidity of the moist air in the ambient on the momentum, heat, and mass transfer in the flow are examined in great detail.

Measurement of thermophysical properties of molten salts: Mixtures of alkaline carbonate salts

Abstract: The purpose of this study is to develop measuring methods for the thermal diffusivity, the specific heat capacity, and the density of molten salts, as well as to measure these properties of mixtures of alkaline carbonate salts. The thermal diffusivity is measured by the stepwise heating method. The sample salt is poured into a thin container, and as a result, a three-layered cell is formed. The thermal diffusivity is obtained from the ratio of temperature rises at different times measured at the rear surface of the cell when the front surface is heated by the stepwise energy from an iodine lamp. The specific heat capacity is measured using an adiabatic scanning calorimeter. The density is measured by Archimedes' principle. Thermal conductivity is determined from the above properties. Measured samples are Li2CO3-K2CO3 (42.7–57.3, 50.0-50.0, and 62.0-38.0 mol%).

Thermal Diffusivity of Partially and Fully Stabilized (Yttria) Zirconia Single Crystals

Abstract: Laser flash measurements of thermal diffusivity of ZrO2 single crystals partially and fully stabilized with Y2O3 were compared with measurements for polycrystalline cubic ZrO2, and single crystals and polycrystals of Al2O3 and MgAl2O4. In general, the thermal diffusivities of the ZrO2 materials examined initially decrease with increasing temperature, although significantly less than for the Al2O3 and MgAl2O4 materials. The diffusivity subsequently rises with increasing temperature for the single crystals of ZrO2 but not for polycrystalline cubic ZrO2, with this increase for ZrO2 crystals occurring at much lower temperatures than for Al2O3 and MgAl2O4 crystals. As the ZrO2 materials went from fully stabilized with 20 wt% Y2O3 to partially stabilized with 5 wt% Y2O3, the room-temperature diffusivity increased from 0.70x10-6 to 0.97x10-6 m2/s. This indicated that the lattice defects, which increase with Y2O3 content, are more important sources of phonon scattering than are the precipitates which appear at lower Y2O3 compositions. On the other hand, at 1000°C the diffusivity of the fully cubic ZrO2 crystals with 20 wt% Y2O3 was 1.10x10-6 m2/s while that of the partially stabilized ZrO2 crystals with 5 wt% Y2O3 was 1.05x10-6 m2/s. The increased diffusivity at higher temperatures can be attributed to radiative heat transfer, with the lower relative diffusivity of the partially stabilized crystals resulting from photon scattering by the precipitate structures present.