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Showing papers on "Thermal diffusivity published in 1989"


Journal ArticleDOI
TL;DR: In this article, the Galerkin/finite element method is employed to solve the equation set of spin-coating process and the formation of a region of extremely low solvent concentration and correspondingly high viscosity and low binary diffusivity at the free surface is predicted.
Abstract: The model of the spin‐coating process presented here accounts for variations of concentration, viscosity, and diffusivity across the thickness of the spin‐coated film. The flow of the liquid is governed by a balance between centrifugal driving force and viscous resisting force. Radial variations in film thickness and concentration are neglected. The Galerkin/finite‐element method is employed to solve the equation set. Film thinning slows initially due to decreasing film thickness and ceases finally due to dramatically increasing viscosity of the coating liquid as solvents evaporate. The formation of a region of extremely low solvent concentration and correspondingly high viscosity and low binary diffusivity at the free surface, i.e., a solid ‘‘skin,’’ is predicted. Coating defects can occur if convective flow has not completely ceased when this skin forms. Skin formation can be eliminated or delayed by partially saturating the overlying gas with solvent or by using mixed solvents (having both high and low...

254 citations


Journal ArticleDOI
01 Jul 1989-Zeolites
TL;DR: In this paper, the authors reviewed the diffusivity data obtained by both macroscopic and microscopic methods for a wide range of zeolitic systems and concluded that both classes of experiment measure intracrystalline migration but on different time scales.

174 citations


Journal ArticleDOI
TL;DR: The thermal diffusion coefficient DT has been obtained for 17 polymer-solvent combinations, each of them spanning a range of polymer molecular weights, using thermal field-flow fractionation as mentioned in this paper.
Abstract: The thermal diffusion coefficient DT has been obtained for 17 polymer-solvent combinations, each of them spanning a range of polymer molecular weights, using thermal field-flow fractionation. The polymers examined include polystyrene, poly(alpha-methyl)styrene, polymethylmethacrylate, and polysioprene. The solvents include benzene, toluene, ethylbenzene, tetrahydrofuran, methylethylketone, ethylacetate, and cyclohexane. Although DT was confirmed as essentially independent of polymer molecular weight, it was found to vary substantially with the chemical composition of polymer and solvent. The results were used to evaluate several thermal diffusion theories; the agreement with theory was generally found to be unsatisfactory. Attempts were then made to correlate the measured thermal diffusion coefficients with various physicochemical parameters of the polymers and solvent. A good correlation was found in which DT increases with the thermal conductivity difference of the polymer and solvent and varies inversely with the activation energy of viscous flow of the solvent.

138 citations


Journal ArticleDOI
TL;DR: In this article, a finite cutoff was incorporated into the asymptotic mode-coupling integrals for the diffusivity associated with the critical fluctuations, which yields a simplified approximation to a more complete nonasymptotic solution of the modecoupled integrals obtained by us earlier.
Abstract: A practical representation for the critical thermal conductivity enhancement is developed by incorporating a finite cutoff into the asymptotic mode-coupling integrals for the diffusivity associated with the critical fluctuations. This procedure yields a simplified approximation to a more complete nonasymptotic solution of the mode-coupling integrals obtained by us earlier. A comparison is made with thermal conductivity data for carbon dioxide, ethane, and methane.

123 citations


Journal ArticleDOI
TL;DR: In this article, three models of different complexity are proposed to describe the falling rate period of the carrot drying process with shrinkage, including a moving or fixed boundary problem as well as a constant or local moisture and temperature dependent effective diffusivity.
Abstract: Three models of different complexity are proposed to describe the falling rate period of the carrot drying process with shrinkage. A moving or fixed boundary problem as well as a constant or local moisture and temperature dependent effective diffusivity are considered. The moving boundary problem is solved by an explicit finite difference method. Heat transfer coefficient and effective diffusivity identification were carried out. The results of the heat transfer coefficient show a good agreement with other sources. Using experimental data and the models. describing the heat and mass transfer three different expressions for the effective diffusivity are established. Two of them are only temperature dependent considering or not particle shrinkage. The third one takes into account temperature and local moisture as well as shrinkage. Drying of foods is a complicated process involving simultaneous coupled heat and mass transfer phenomena which occur inside the material being dried (Chiang and Petersen...

122 citations


Journal ArticleDOI
TL;DR: In this paper, the expected magnetic field structure is described and experimental evidence of the existence of this structure is presented, and the implied increase in edge electron thermal diffusivity is compared with theoretical expectations and is shown to agree with applicable theories to within a factor of three.
Abstract: Externally applied magnetic fields are used on the Texas Experimental Tokamak (TEXT) to study the possibility of controlling the particle, impurity and heat fluxes at the plasma edge. Fields with toroidal mode number n = 2 or 3 and multiple poloidal mode numbers m (dominantly m = 7) are used, with a poloidally and toroidally averaged ratio of radial to toroidal field components 〈|br/Bo〉 ≅0. 1%. Calculations show that it is possible to produce mixed islands and stochastic regions at the plasma edge (r/a ≥ 0.8) without affecting the interior. The expected magnetic field structure is described and experimental evidence of the existence of this structure is presented. The edge electron temperature decreases with increasing 〈|br/Bo〉, while interior values are not significantly affected. The implied increase in edge electron thermal diffusivity is compared with theoretical expectations and is shown to agree with applicable theories to within a factor of three.

112 citations


Book ChapterDOI
01 Jan 1989
TL;DR: In this paper, a PC-based probe apparatus is presented for simultaneous measurement of thermal conductivity and thermal diffusivity of foods, and a structural model that accounts for the component arrangement in the system is proposed.
Abstract: This report outlines thermal property measurement techniques and thermal property modelling of foods. The discussion on measurement technique focuses on thermal conductivity and thermal diffusivity only. Since thermal conductivity and thermal diffusivity measurements are based on the heat transfer mechanism, measurement apparatus is specifically designed for certain materials and environmental conditions. The probe technique designed for simultaneous measurement of thermal conductivity and thermal diffusivity has been one of the most widely used because it can be easily operated, and commercially produced. A PC-based probe apparatus is presented. Published models on thermal conductivity prediction are grouped according to their appropriate food system. It is proposed in this study that the thermal conductivity model of foods be made up of its components and a structural model that accounts for the component arrangement in the system. The Keey model was found the best structural model for porous foods while the parallel-perpendicular model worked well for frozen nonporous system. This model was also appropriate for meat measured along the fibers at above freezing temperatures. The rest of nonporous foods was found best predicted with the parallel model.

108 citations


Journal ArticleDOI
Christina Rask1
TL;DR: In this article, a review of the thermal properties of dough, bread and bakery products is presented, together with an overview of the literature in this field to facilitate the estimation of values for the properties of a product of known moisture content and density.

102 citations


Journal ArticleDOI
TL;DR: In this paper, a complete theoretical treatment of the "mirage" (optical beam deflection) technique has been performed for thermal diffusivity measurements in solids, and the experimental limits which make a sample to be considered as an opaque or transparent and as thermally thick or thin, and present a complete classification of solids according to their optical and thermal properties.
Abstract: A complete theoretical treatment of the ‘‘mirage’’ (optical beam deflection) technique has been performed for thermal diffusivity measurements in solids. Numerical calculations of the transverse deflection show there is a linear relation between the first noncentral zeros of the real part of this function and the inverse root frequency. The slope of this straight line is related to the thermal diffusivity through a factor (γ) which depends on the thermal and optical properties of the sample. We found γ=1 for transparent materials as well as for opaque thermally thin materials, whereas γ=1.44 for opaque thermally thick samples. We study further the experimental limits which make a sample to be considered as an opaque or transparent and as thermally thick or thin, and present a complete classification of solids according to their optical and thermal properties. The different behaviors observed may be related to the different geometry of thermal waves propagating through the media.

101 citations


Journal ArticleDOI
TL;DR: In this paper, a gravity drainage concept has been proposed and tested for in-situ recovery of bitumen by mobilization with soluble gases at ambient reservoir temperature conditions Experiments were done using carbon dioxide and ethane gases at ∼ 20°C to recover Athabasca bitumen from a scaled reservoir model.
Abstract: A gravity drainage concept has been proposed and tested for in-situ recovery of bitumen by mobilization with soluble gases at ambient reservoir temperature conditions Experiments were done using carbon dioxide and ethane gases at ∼ 20°C to recover Athabasca bitumen from a scaled reservoir model Thermal gravity drainage theory has been modified for the mass transfer case The measured drainage rates were higher than those predicted by the model using molecular diffusivity data but fit the model better using an increased effective diffusivity Lateral dispersion theory does not predict the high measured effective diffusivities A preliminary economic evaluation of field production indicates potential application to recovery of Lloydminster heavy oil

96 citations


Journal ArticleDOI
TL;DR: In this article, the phase stability of zirconia alloyed with 12, 15, 20, 20 and 25 wt.% yttria was determined by X-ray diffraction.
Abstract: Coatings consisting of zirconia alloyed with 12, 15, 20 and 25 wt.% ceria or 4, 6, 8, 10 and 12 wt.% yttria were prepared using the plasma spray process. For each of these coatings measurements were made of thermal expansion parallel to the substrate and of thermal conductivity perpendicular to the substrate. These results are discussed in conjunction with the phase stability of the specimens, as determined by X-ray diffraction. Coatings containing 25 wt.% ceria or greater than 8 wt.% yttria were found to have stable thermal properties. Coatings containing less of these additions exhibited a thermal expansion hysterisis which was most pronounced at the lowest concentrations. The temperature at which the hysterisis occured was found to reduce with increasing additions of alloying agent. This behaviour was also detected for ZrO2−CeO2 as a change in thermal diffusivity during thermal cycling and is attributed to a reversible tetragonal-monoclinic transformation.

Journal ArticleDOI
TL;DR: In this paper, the effects exerted on the motion and on heat and mass transfer of particulates injected into a thermal plasma are discussed, including an assessment of their relative importance in the context of thermal plasma processing of materials.
Abstract: In this overview, effects exerted on the motion and on heat and mass transfer of particulates injected into a thermal plasma are discussed, including an assessment of their relative importance in the context of thermal plasma processing of materials. Results of computer experiments are shown for particle sizes ranging from 5–50 μm, and for alumina and tungsten as sample materials. The results indicate that (i) the correction terms required for the viscous drag and the convective heat transfer due to strongly varying properties are the most important factors; (ii) noncontinuum effects are important for particle sizes <10 μm at atmospheric pressure, and these effects will be enhanced for smaller particles and/or reduced pressures; (iii) the Basset history term is negligible, unless relatively large and light particles are considered over long processing distances; (iv) thermophoresis is not crucial for the injection of particles into thermal plasmas; (v) turbulent dispersion becomes important for particle <10 μm in diameter; and (vi) vaporization describes a different particle heating history than that of the evaporation process which, however, is not a critical control mechanism for interphase mass transfer of particles injected into thermal plasmas.

Journal ArticleDOI
Sun Xiukui1, Xu Jian1, LI Yiyi1
TL;DR: In this paper, the authors investigated the effect of cold-working and heat treatment conditions and the alloy composition of the materials on hydrogen permeability and diffusivity in six types of austenitic stainless steel.
Abstract: The permeability, diffusivity and solubility of hydrogen in six types of austenitic stainless steel—316L, 316LN, 21-6–9, 21-9-9, 304 and 321—have been measured by a gaseous permeation technique in the temperature range 200–430°C. The effect of the cold-working and heat treatment conditions and the alloy composition of the materials on hydrogen permeation has been investigated. The results indicate that the permeability and diffusivity of hydrogen in various alloys obey Arrhenius relationships over the experimental temperature range and the hydrogen permeation behaviour is not significantly influenced by cold-working and heat treatment conditions of the materials but is slightly influenced by alloy composition. The difference between the hydrogen permeation behaviour of pure iron, general alloying steels and austenitic stainless steels has been discussed, and a comparison between the present work and data in the literature has been made.

Journal ArticleDOI
01 Jul 1989-Fuel
TL;DR: In this article, the thermal properties of coal slags formed in the British Gas/Lurgi slagging gasifier have been measured for temperatures between 298 and 1800 K. The authors derived values of heat capacity and enthalpy using a model relating the property value to the chemical composition of the slag and these were found to be in good agreement with experimental data.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the mass transfer behavior of a suite of six volatile halogenated organic compounds and oxygen in a laboratory scale reactor representative of mechanical surface aeration during activated sludge treatment.

Journal ArticleDOI
TL;DR: In this article, an incompressible fluid model of the Rayleigh-Taylor instability is generalized to include self-consistent diffuse boundaries, which can predict the scaling of the instability cutoff over an extended parameter range and its dependence on the heat conduction law.
Abstract: An incompressible fluid model of the ablative Rayleigh–Taylor instability [Phys. Fluids 29, 2067 (1986)] is generalized to include self‐consistent diffuse boundaries. With diffuse boundaries the incompressible model is found to be in excellent agreement with a number of previous stability studies of laser ablation. The present theory can predict the scaling of the instability cutoff over an extended parameter range and its dependence on the heat conduction law. It is found that more favorable stability behavior can be obtained both for weak and strong thermal diffusion. Furthermore a strong dependence of the stabilization mechanism on the functional form of the heat conductivity is indicated. Representative conditions for laser ablation are identified and discussed in detail.

Journal ArticleDOI
TL;DR: The effective diffusivity of oxygen decreased with increasing cell density, to Cc = 170 kg dry cells/m3 gel, and the dependency of De on cell density was discussed in terms of a random‐pore model.
Abstract: The effective diffusivity of oxygen, D(e), in Ca-alginate and PVA-SbQ gels was measured using a two-chamber vessel with a membrane between the two chambers. The effect of cell density, C(c), on D(e) in Ca-alginate gels was studied. The effective diffusivity of oxygen decreased with increasing cell density, to C(c) = 170 kg dry cells/m(3) gel. The dependency of D(e) on cell density was discussed in terms of a random-pore model. The model correlated well with experimental data, i.e., kD(e)/D(0) = 0.86(1 - 1.47 x 10(-3) C(c))(2). Here, k is the partition coefficient, and D(0) is diffusivity in water.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed possible causes of the observed spreading of sample components which degrades separation compared with theoretical limits, and identified four potentially significant causes, electrokinetic dispersion, wall adsorption, enhanced diffusion due to Poiseuille flows driven by pressure gradients, and enhanced diffusion because of mobility variations associated with transverse temperature differences.

Journal ArticleDOI
TL;DR: A method for determining the macroscopic diffusivity D, which, in principle, is exact, is developed and found to be similar to/exp(-a/r/sub m/), independent of the morphology of the medium or the microscopic transport laws.
Abstract: The results of the first computer simulations of transport of macromolecules in a disordered porous medium, represented by a network of capillary tubes with random radii, are reported. We develop a method for determining the macroscopic diffusivity D which, in principle, is exact. The effects of both convection and diffusion are taken into account. We find D/D/sub infinity//similar to/exp(-a/r/sub m/), independent of the morphology of the medium or the microscopic transport laws, where a is the effective size of the molecules, D/sub infinity/ the diffusivity in an unbounded solvent, and r/sub m/ the mean effective size of the pores, consistent with experimental data.

Journal ArticleDOI
TL;DR: In this paper, the authors revisited the calculation of thermal diffusivity induced by resistive pressure gradient driven turbulence and showed that the relevant correlation length for the magnetic fluctuations is different from estimates made with a mixing-length approach and with dimensional analysis.
Abstract: The calculation of the thermal diffusivity induced by resistive pressure‐gradient‐driven turbulence is revisited. The relevant correlation length for the magnetic fluctuations is shown to be different from estimates made with a mixing‐length approach and with dimensional analysis. This leads to different scaling predictions for the electron heat diffusivity. The root of this difference is the fact that the flux and current perturbations are related by two scale lengths, the poloidal wavelength and the mode width.


Journal ArticleDOI
TL;DR: Central ion temperatures up to 30 keV and rotation speeds up to 8/times/10/sup 5/ m/sec have been confirmed with new diagnostic measurements in the TFTR hot-ion enhanced-confinement regime, and the ion thermal diffusivity is found to be non-neoclassical and comparable to the anomalous electron thermal diffuse.
Abstract: Central ion temperatures up to 30 keV and rotation speeds up to 8/times/10/sup 5/ m/sec have been confirmed with new diagnostic measurements in the TFTR hot-ion enhanced-confinement regime, and the ion thermal diffusivity is found to be non-neoclassical and comparable to the anomalous electron thermal diffusivity. The dominant effect of strong rotation is the down-shifting of the neutral beam energies in the plasma frame, which results in reduced ion and electron heating on axis, and the presence of off-axis ion heating from viscous damping of the plasma rotation.

Journal Article
TL;DR: In this paper, the thermal properties of different concretes were evaluated with particular reference to their dependence on some other properties of the material such as density, water content, temperature, and type of aggregate.
Abstract: This paper presents experimental work concerning evaluation of the thermal properties of different concretes, with particular reference to their dependence on some other properties of the material such as density, water content, temperature, and type of aggregate. Both mortar and concrete samples have been tested. Measurements of thermal properties have been performed on each sample from a fully saturated to an oven-dry condition. To avoid water migration during the run-time of the thermal tests, a transient measurement method has been used. Two linear parallel probes inserted in the specimen allow the simultaneous measurement of thermal conductivity and thermal diffusivity

Journal ArticleDOI
TL;DR: In this article, the effective diffusivity of water (D) in hydrated mixtures of two granular starches and three sugars (glucose, sucrose and dextrin) was investigated in the temperature range 40-100°C.
Abstract: The effective diffusivity of water (D) in hydrated mixtures of two granular starches and three sugars (glucose, sucrose and dextrin) was investigated in the temperature range 40-100°C. Spherical samples (2-cm diameter) of the hydrated mixtures were air-dried at controlled conditions and the D values at various moistures were estimated from the slopes of the drying curves. The sugars reduced significantly the D values in proportion to their molecular size. The changes in water diffusivity were related to the porosity of the samples. Temperature had an Arrhenius-type effect, and the estimated energies of activation for diffusion of water increased significantly by the addition of sugars.

Journal ArticleDOI
TL;DR: In this article, the temperature-dependent equilibrium Ga vacancy diffusivity was obtained by using an ensemble Monte Carlo simulation, and the resulting expression is 1.25×1031 exp(−3.28/kBT) cm2/s.
Abstract: Intermixing of AlGaAs‐based interfaces is known to be enhanced by capping wafers with a layer of SiO2. Assuming that this enhancement results from the introduction of additional Ga vacancies into the sample, it is possible to obtain the temperature‐dependent equilibrium Ga vacancy diffusivity. Experiments are performed whereby SiO2‐capped quantum well samples are annealed at temperatures ranging from 800 to 1025 °C. Calculated photoluminescence shifts are compared with the measured spectra, and a relation for the Ga vacancy diffusivity of the form 0.962 exp(−2.72/kBT) cm2/s is obtained. Using this relation, the equilibrium Ga vacancy concentration can be computed via an ensemble Monte Carlo simulation. The resulting expression is 1.25×1031 exp(−3.28/kBT) cm−3.

Journal ArticleDOI
TL;DR: In this article, a perturbation analysis is used to show how the balance between the processes of selective diffusional demixing and flame stretch readily accounts for the composition domains in which cellular flames occur, and also predicts their dimensions.

Journal ArticleDOI
TL;DR: In this paper, a thermal Mach number M defined as the ratio between the speed of the moving heat source and that of the heat propagation in the solid is introduced, and the resulting energy equation is found to be elliptic, parabolic, and hyperbolic in the subsonic (M M = 1), and supersonic ( M > 1) ranges, respectively.

Journal ArticleDOI
TL;DR: The thermal release behavior of tritium produced in neutron-irradiated Li2O, γ-LiAlO2, Li2SiO3, Li 4SiO4, Li 2ZrO3 and Li 8Zr O6 crystals was studied in this paper.

Journal ArticleDOI
01 Feb 1989
TL;DR: In this paper, the authors investigated the uptake of water in quartz at 15 GPa total pressure, 1173 K and high water fugacity, over times up to 24 hours, using a newly developed assembly to prevent microcracking.
Abstract: The uptake of water in quartz at 15 GPa total pressure, 1173 K and high water fugacity, over times up to 24 h, has been investigated using a newly developed assembly to prevent microcracking It is found that the uptake is small, and below the detectability of the presently used technique of infrared spectroscopy and serial sectioning This observation reflects either a low value for the diffusivity or the solubility or a combination of both, and is in agreement with the observations of Kronenberg et al (1986) and Rovetta et al (1986) It brings into question the interpretation of the early experiments on water weakening by Griggs and Blacic (1964) and the recent estimates of the solubility and diffusivity by Mackwell and Paterson (1985)

Journal ArticleDOI
TL;DR: In this article, the authors analyzed the melting and freezing that can occur when a very large layer of hot fluid begins to flow turbulently over a cold solid retaining boundary and determined the evolution of the solidified region and showed that with time it will be totally remelted.
Abstract: We analyse the melting and/or freezing that can occur when a very large layer of hot fluid begins to flow turbulently over a cold solid retaining boundary. This is a form of Stefan problem and the response is determined by the balance between the turbulent heat flux from the fluid, H, and the (initially infinite) conductive flux into the solid. We show that solidification of the flow at the boundary must always occur initially, unless the freezing temperature of the fluid, Tf, is less than the initially uniform temperature, T0, of the semi-infinite solid. We determine the evolution of the solidified region and show that with time it will be totally remelted. Melting and ablation of the solid retaining boundary will then generally follow, unless its melting temperature exceeds that of the turbulent flow. The maximum thickness of the solidified crust is shown to scale with k2(Tf − T0)2/ρkHL and its evolution takes place on a timescale of k2(Tf − T0)2/kH2, where k is the thermal conductivity, k the thermal diffusivity, ρ the density and L the latent heat, with all these material properties assumed to be equal for fluid and solid.