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Showing papers on "Thermal diffusivity published in 1982"


Journal ArticleDOI
TL;DR: In this paper, the effects of flow inhomogeneities on the dynamics of laminar flamelets in turbulent flames, with account taken of influences of the gas expansion produced by heat release, were investigated.
Abstract: To study effects of flow inhomogeneities on the dynamics of laminar flamelets in turbulent flames, with account taken of influences of the gas expansion produced by heat release, a previously developed theory of premixed flames in turbulent flows, that was based on a diffusive-thermal model in which thermal expansion was neglected, and that applied to turbulence having scales large compared with the laminar flame-thickness, is extended by eliminating the hypothesis of negligible expansion and by adding the postulate of weak-intensity turbulence. The consideration of thermal expansion motivates the formal introduction of multiple-scale methods, which should be useful in subsequent investigations. Although the hydrodynamic-instability mechanism of Landau is not considered, no restriction is imposed on the density change across the flame front, and the additional transverse convection correspondingly induced by the tilted front is described. By allowing the heat-to-reactant diffusivity ratio to differ slightly from unity, clarification is achieved of effects of phenomena such as flame stretch and the flame-relaxation mechanism traceable to transverse diffusive processes associated with flame-front curvature. By carrying the analysis to second order in the ratio of the laminar flame thickness to the turbulence scale, an equation for evolution of the flame front is derived, containing influences of transverse convection, flame relaxation and stretch. This equation explains anomalies recently observed at low frequencies in experimental data on power spectra of velocity fluctuations in turbulent flames. It also shows that, concerning the diffusive-stability properties of the laminar flame, the density change across the flame thickness produces a shift of the stability limits from those obtained in the purely diffusive-thermal model. At this second order, the turbulent correction to the flame speed involves only the mean area increase produced by wrinkling. The analysis is carried to the fourth order to demonstrate the mean-stretch and mean-curvature effects on the flame speed that occur if the diffusivity ratio differs from unity.

452 citations


Journal ArticleDOI
TL;DR: In this paper, two models of advection-diffusion in the oscillatory, sheared-velocity field of an internal wave are discussed and the authors develop intuition about the role of such currents in horizontal ocean mixing through the mechanism of shear dispersion.
Abstract: Two models of advection-diffusion in the oscillatory, sheared-velocity field of an internal wave are discussed. Our goal is to develop intuition about the role of such currents in horizontal ocean mixing through the mechanism of shear dispersion. The analysis suggests simple parameterizations of this process, i.e., those in Eqs. (7), (36) and (42). The enhanced horizontal diffusion due to the interaction of the vertical diffusion and vertical shear of the wave field can be described by an “effective horizontal diffusivity” which is equal to the actual horizontal diffusivity plus a term equal to the mean-square vertical shear of horizontal displacement times the vertical diffusivity, provided the vertical length scale of the horizontal velocity field is not too small. In the limit of small vertical length scale the expression reduces to Taylor's (1953) result in which the effective horizontal diffusivity is inversely proportional to the actual vertical diffusivity. The solutions also incidentally ...

244 citations


Journal ArticleDOI
TL;DR: In this article, a computational procedure for predicting velocity and temperature distributions in enclosures containing a fire source is reported, based on the solution, in finite-difference form, of the 2-dim.

242 citations


Journal ArticleDOI
TL;DR: In this article, the chemical potential and diffusivity of interstitial solute atoms were calculated for disordered materials in a general way, and compared with corresponding special theoretical results which are mostly related to attractive interaction (trapping) and repulsive interaction (antitrapping) between interstitially and substitutionally dissolved impurity atoms.

241 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of intrinsic point defects on the diffusion-controlled growth of oxygen precipitates is investigated in some detail, and the concept of molecular oxygen is invoked in a newly suggested model of thermal donor formation in silicon.
Abstract: The information available on the diffusion of oxygen and on the formation of thermal donors in silicon is critically reviewed. In this context the effects of intrinsic point defects on the diffusion-controlled growth of oxygen precipitates is investigated in some detail. Seemingly contradictory experimental results on the diffusivity of oxygen in silicon at temperatures around 400° C are explained in terms offast-diffusing gas-like molecular oxygen in silicon. The concept of molecular oxygen is also invoked in a newly suggested model of thermal donor formation in silicon. The diffusivity of molecular oxygen in silicon is estimated to be around 10−9cm2s−1 at 450° C, almost nine orders of magnitude higher than the diffusivity of atomic oxygen in interstitial position.

238 citations


Journal ArticleDOI
TL;DR: In this paper, the authors developed a one-dimensional model for thermal wave depth profiling that provides expressions for the temperature at the surface of the sample and for the thermoelastic response beneath the surface.
Abstract: We have developed a one‐dimensional model for thermal‐wave depth profiling that provides expressions for the temperature at the surface of the sample and for the thermoelastic response beneath the surface. The model shows that elastic wave interference effects produce significant differences between samples with mechanically free and constrained surfaces, and that thermal‐ wave images of thermal conductivity variations are obtainable from the thermoelastic signal only if the front surface is mechanically free. We have also considered the case of subsurface heating and found that for heating occurring at depths of more than a few thermal diffusion lengths, the thermoelastic signal becomes independent of thermal conductivity variations. This has important implications for thermal‐wave image range and resolution.

236 citations


Journal ArticleDOI
TL;DR: In this article, the authors present calculations of the temperature profiles induced by a moving cw elliptical laser beam with a Gaussian intensity distribution in a semi-infinite material.
Abstract: We present calculations of the temperature profiles induced by a moving cw elliptical laser beam with a Gaussian intensity distribution in a semi‐infinite material. Temperature‐dependent thermal diffusivity, conductivity, and surface reflectivity are incorporated in our model, and some aspects of melting are discussed. As an example, we apply the calculations to silicon. For a comparison of stationary elliptical spots of varying eccentricities, we present material‐independent normalized linear temperature profiles. We find that highly elliptical beams can be used to rapidly scan and anneal large areas.

234 citations


Journal ArticleDOI
TL;DR: In this article, a free-volume theory of polymer-solvent diffusion coefficients is proposed and evaluated using experimental diffusivity data collected over wide temperature and concentration ranges, showing that the theory accurately predicts the large temperature variations typically observed for polymer solvents diffusion coefficients.
Abstract: A revised version of a recently proposed free-volume theory of polymer-solvent diffusion is introduced and evaluated using experimental diffusivity data collected over wide temperature and concentration ranges. The theory accurately predicts the large temperature and concentration variations typically observed for polymer-solvent diffusion coefficients.

226 citations


Journal ArticleDOI
TL;DR: In this paper, a consistent interpretation of the results is given within the framework of a Fermi-Dirac statistics, developed and used recently for the interaction of hydrogen with defects in solids.

225 citations


Journal ArticleDOI
TL;DR: In this paper, the photoacoustic method was used to measure the thermal diffusivities of metals by using rear surface illumination and a sufficiently high modulation frequency to prevent mechanical vibrations of the sample due to its periodic dilatation.
Abstract: Thermal diffusivities of metals can be accurately measured by the photoacoustic method. It is necessary, however, to use rear‐surface illumination and to work at sufficiently high modulation frequency. Furthermore, to prevent mechanical vibrations of the sample due to its periodic dilatation (’’drum effect’’), this sample must be carefully fixed on the backing.

175 citations


Journal ArticleDOI
TL;DR: In this article, the diffusivity of oxygen in silicon during steam oxidation at 700-1240°C was measured on asoxidized Si wafers, and the results were compared with previous literature values measured only at high temperature.
Abstract: The diffusivity of oxygen in silicon during steam oxidation at 700–1240 °C was measured on as‐oxidized Si wafers. To provide greater analytical sensitivity 18O was introduced into the float‐zone Si wafers from 1‐atm H2 18O steam, and the 18O depth profiles were measured by Cs+ secondary ion mass spectrometry. Over the entire temperature range studied, the diffusivity is governed by a single activation energy, 2.44 eV, and the prefactor is 7×10−2 cm2 s−1. Our results are compared with previous literature values measured only at high temperature.

Journal ArticleDOI
TL;DR: In this paper, the authors consider the effect of Taylor's longitudinal diffusivity in turbulent flow in a flat-bottomed channel of large aspect ratio, for which arguments based on physics are adduced in support of the formula D≈[1 + B][1 - λ(b/u)], where B and λ are positive constants independent of b.
Abstract: In a recent paper Doshi, Daiya & Gill (1978) showed that the value of Taylor's longitudinal diffusivity D for laminar flow in a channel of rectangular cross-section of breadth u and height b is about 8D0, for large values of the aspect ratio a/b, where Do is the value of the longitudinal diffusivity obtained by ignoring all variation across the channel. This superficially surprising result is confirmed by an independent method, and is shown to be caused by the boundary layers on the side walls of the channel. The primary purpose of the paper, however, is to consider the value of D in turbulent flow in a flat-bottomed channel of large aspect ratio, for which arguments based on physics are adduced in support of the formula D≈[1 + B][1 - λ(b/u)], where B and λ are positive constants independent of b. It is shown that this result is consistent with laboratory experiments by Fischer (1966). The paper concludes with a discussion of the practical effects of aspect ratio on longitudinal dispersion in channels whose cross-section is approximately rectangular.

Journal ArticleDOI
TL;DR: In this paper, a complete model taking into account intraparticle diffusion and forced convection together with film diffusion is derived in order to analyze diffusivity measurements by physical methods, both in perfectly mixed reactors and fixed beds.
Abstract: Intraparticle forced convection was considered in order to explain experimentally observed changes in effective diffusivity (apparent) with flowrate, when measures are carried out in fixed beds. A complete model taking into account intraparticle diffusion and forced convection together with film diffusion is derived in order to analyze diffusivity measurements by physical methods, both in perfectly mixed reactors and fixed beds. The experiments were carried out with hydrogen tracer in a partial oxydation catalyst. Implications of the use of such “apparent” effective diffusivities in reactor design are discussed, showing that errors of 100% can be made.

Journal ArticleDOI
TL;DR: In this paper, a mechanistic model of transport through an elastic medium is adapted to the present data and a strong correlation of E with ionic radius and squared formal charge (Z2) offers guidelines for model calculation of the activation energy.
Abstract: Tracer diffusivity of Na, K, Rb, Cs, Ca, Sr, Ba, Eu, and Ce has been measured in natural and dehydrated obsidians in the range 300°–1300°C, 0–4 kbar, using radiotracers and an etching technique. The results complement and extend previous results on similar material. Diffusivity ranging from 10−16 to 10−7 cm2/s have been observed. An Arrhenius law is observed for all species, with activation energies E ranging from 20 to 120 kcal/mol. A strong correlation of E with ionic radius and squared formal charge (Z2) offers guidelines for model calculation of the activation energy. A mechanistic model of transport through an elastic medium is adapted to the present data. It permits a fair prediction of the activation energy as a function of r and Z according to E = 128(r−1.34)2 + 33 Z2/(r+1.34) + 8 kcal/mol, with a misfit comparable to the experimental uncertainty. The correlation between E and the preexponential factor Do (compensation law) is discussed within the framework of the proposed model. The major conclusion is that local configuration (size, charge, coordination, etc.) is the major control for cationic diffusivity and not the properties of the matrix, such as chemical composition, viscosity, etc.

Journal ArticleDOI
TL;DR: In this paper, an analytical study of the heat and mass transfer process of a single particle exposed to a thermal plasma, with emphasis on the effects which evaporation imposes on heat transfer from the plasma to the particle, is presented.
Abstract: This paper is concerned with an analytical study of the heat and mass transfer process of a single particle exposed to a thermal plasma, with emphasis on the effects which evaporation imposes on heat transfer from the plasma to the particle. The results refer mainly to an atmospheric-pressure argon plasma and, for comparison purposes, an argon-hydrogen mixture and a nitrogen plasma are also considered in a temperature range from 3000 to 16,000 K. Interactions with water droplets, alumina, tungsten, and graphite particles are considered in a range of small Reynolds numbers typical for plasma processing of fine powders. Comparisons between exact solutions of the governing equations and approximate solutions indicate the parameter range for which approximate solutions are valid. The time required for complete evaporation of a given particle can be determined from calculated values of the vaporization constant. This constant is mainly determined by the boiling (or sublimation) temperature of the particles and the density of the condensed phase. Evaporation severely reduces heat transfer to a particle and, in general, this effect is more pronounced for materials with low latent heat of evaporation.

Journal ArticleDOI
TL;DR: In this article, a linear analysis of the hydrodynamic stablity of the plane flame front of a premixed laminar flame is presented, and the technique of outer and inner asymptotic expansions is used to calculate the next approximation to the classical long-wave Landau limit.
Abstract: This paper presents a linear analysis of the hydrodynamic stablity of the plane flame front of a premixed laminar flame. The technique of outer and inner asymptotic expansions is used to calculate the next approximation to the classical long-wave Landau limit. The resulting correction turns out to be independent of the Prandtl number. This implies that, although diffusivity, conductivity and viscosity in gases are of the same order of magnitude, viscosity exerts a secondary influence in comparison with diffusivity and conductivity.

Journal ArticleDOI
H. Kashiwagi1, T. Hashimoto1, Yoshiaki Tanaka1, Hironobu Kubota1, T. Makita1 
TL;DR: In this article, the Tait-type equations and empirical polynomials for thermal conductivity and density of liquid toluene were presented in the temperature range 0 −100°C at pressures up to 250 MPa.
Abstract: New experimental data on the thermal conductivity and the density of liquid toluene are presented in the temperature range 0–100°C at pressures up to 250 MPa. The measurements of thermal conductivity were performed with a transient hot-wire apparatus on an absolute basis with an inaccuracy less than 1.0%. The density was measured with a high-pressure burette method with an uncertainty within 0.1%. The experimental results for both properties are represented satisfactorily by the Tait-type equations, as well as empirical polynomials, covering the entire ranges of temperature and pressure. Furthermore, it is found that simple relations exist between the temperature dependence of thermal conductivity and the thermal expansion coefficient, and also between the pressure dependence of thermal conductivity and the isothermal compressibility, as are suggested theoretically.

Journal ArticleDOI
TL;DR: In this article, a model of lithospheric thinning is presented, in which heat is convected to the base and conducted within the lithosphere, and an analytical equation for determinining the amount of thinning attainable on increasing the heat flux from the asthenosphere is derived, and a formula for lithosphere thickness approximations as a function of time is given.
Abstract: A model of lithospheric thinning, in which heat is convected to the base and conducted within the lithosphere, is presented. An analytical equation for determinining the amount of thinning attainable on increasing the heat flux from the asthenosphere is derived, and a formula for lithosphere thickness approximations as a function of time is given. Initial and final equilibrium thicknesses, thermal diffusivity, transition temperature profile, and plume temperature profile are all factors considered for performing rate of thinning determinations. In addition, between initial and final equilibrium states, lithospheric thinning occurs at a rate which is inversely proportional to the square root of the time. Finally, uplift resulting from thermal expansion upon lithospheric thinning is on the order of 10 to the 2nd to 10 to the 3rd m.

Journal ArticleDOI
TL;DR: In this article, the specific heat, the entropy, the thermal conductivity and the diffusivity of Gd 3 Ga 5 O 12 have been measured in the presence of an applied magnetic field.

Journal ArticleDOI
TL;DR: In this article, the diffusion of arsenic in polycrystalline silicon films has been studied over the temperature range 750-950 °C and for grain sizes 210-510 nm.
Abstract: The diffusion of arsenic in polycrystalline silicon films has been studied over the temperature range 750–950 °C and for grain sizes 210–510 nm. Rutherford backscattering spectrometry was used to measure the concentration profiles of arsenic, initially introduced into the polysilicon by ion implantation, after various annealing steps. The concentration profiles were found to be determined by a combination of two factors—the low diffusivity in the bulk of the rains and the much higher diffusivity in the grain boundaries. The diffusivity of arsenic in the grain boundaries was independent of concentration, with an activation energy of 3.9 eV, very close to that of the low‐concentration arsenic diffusivity in single‐crystal silicon. However, the value of the diffusivity was 8.6×104 exp(−3.9/kT)cm2/s, four orders of magnitude higher than the single‐crystal value. The diffusivity in the interior of the grains was the same as that in single‐crystal silicon.

Journal ArticleDOI
TL;DR: In this paper, a spherical continuous stirred tank (SSTC) was used to measure the particle wall loss rate in a particle diffusivity, particle settling velocity, and vessel radius.
Abstract: Aerosol particle wall loss rates were determined experimentally in a spherical continuous stirred tank reactor. Tbe particle size and mixing rate dependences are shown to agree with β=12k_eD/Rπvʃ^nv/2√k_2D_0 te^t/e^t-1dt+v/4R3 the theoretical result of Crump and Seinfeld, in which the particle loss coefficient β is related to particle diffusivity D, particle settling velocity r, the coefficient of the eddy diffusivity k_e, and vessel radius R. For the vessel used in these experiments, k_e was found to be proportional to the 3/2 power of the volumetric now rate, in accordance with theoretical expectations. Results of a similar nature may be expected to hold in vessels of arbitrary shape.

Journal ArticleDOI
TL;DR: In this paper, a mathematical model has been developed to determine the temperature distribution in the wall of a rotary kiln, which incorporates a detailed formulation of the radiative and convective heat transfer coefficients in a kiln.
Abstract: A mathematical model has been developed to determine the temperature distribution in the wall of a rotary kiln. The model, which incorporates a detailed formulation of the radiative and convective heat-transfer coefficients in a kiln, has been employed to examine the effect of different kiln variables on both the regenerative and the overall heat transfer to the solids. The variables include rotational speed, pct loading, temperature of gas and solids, emissivity of wall and solids, convective heattransfer coefficients at the exposed and covered wall, and thermal diffusivity of the wall. The model shows that the regenerative heat flow is most important in the cold end of a rotary kiln, but that generally the temperature distribution and heat flows are largely independent of these variables. Owing to this insensitivity it has been possible to simplify the model with the aid of a resistive analog. Calculations are presented indicating that both the shell loss and total heat flow to the bed may be estimated to within 5 pct using this simplified model.

Journal ArticleDOI
TL;DR: In this paper, the effect of temperature on the physical and mechanical properties of typical steels and concretes which are used in PCRV design are presented, and special consideration has been given to the properties and phenomena concerning thermal behaviour, e.g. thermal diffusivity and conductivity, specific heat, density, thermal expansion and decomposition effects.

Journal ArticleDOI
TL;DR: In this paper, the diffusion parameters of Zr-V alloys were studied in the temperature ranges 1166-1480 K and 1167-1476 K, respectively, using the sectioning method.
Abstract: Solute and solvent diffusion in Zr-V alloys (V∼0–2 at.%) have been studied in the temperature ranges 1166–1480 K and 1167–1476 K, respectively, using the sectioning method. With increasing V content, the diffusion parameters D0 and Q for 48V diffusion vary from 8·9 to 0·7 × 10−9 m2 s−1 and 116·55 to 94·16 kJ mol−1, respectively, while for 95Zr diffusion they vary from 3·1 to 14·0 × 10−9 m2 s−1 and 105·25 to 120·79 kJ mol−1. With increasing solute content, the solute diffusivity decreases throughout the temperature range, whereas the solvent diffusivity decreases below 1223 K and increases above it. At 1223 K, there is a transition from solute vacancy repulsion to solute vacancy attraction. The values of the impurity correlation factor are consistent with the vacancy mechanism of diffusion.

Journal ArticleDOI
TL;DR: A critical review of the methods for the measurement of thermal conductivity and thermal diffusivity of foodstuffs is given in this article, where the physical-mathematical basis for the methods is outlined and the methods are classified according to the position of the heat source and heat sink with respect to the sample, the duration of the measurement run and the mathematical procedure involved.

Journal ArticleDOI
TL;DR: The diffusivity of copper in thin TiN layers was determined in specimens prepared by r.f. sputtering a copper layer onto a TiN (200 nm) layer on sapphire and silicon substrates.

Journal ArticleDOI
TL;DR: In this article, the authors formulated the moisture diffusion in unidirectional fiber-reinforced composite materials in terms of relative moisture concentration which responds to the temperature for the heat conduction problem.
Abstract: The moisture diffusion in unidirectional fiber-reinforced composite materials is formulated in terms of relative moisture concentration which cor responds to the temperature for the heat conduction problem. And the effec tive transverse moisture diffusivity of the composite materials with random array packing of fibers is predicted based on the properties of the constituent matrix and fibers by establishing a random array model. It is found that if the degree of randomness increases, the transverse diffusivity decreases remarkably. The theoretical prediction is in good agreement with the ex perimental data obtained by the authors and other researchers. And the analogy between the moisture diffusion and the thermal conduction or the longitudinal shear loading is discussed, pointing out some error in similarity used to predict the moisture diffusivity of composite materials in the literature.

Journal ArticleDOI
TL;DR: Gouy interferometry was employed to measure diffusion coefficients in undersaturated and supersaturated aqueous urea solutions at 25°C as discussed by the authors, where the use of laser light as a monochromatic light source in the interferometer greatly simplified the procedure for obtaining diffusivity data.
Abstract: A relatively simple and extremely versatile optical method of obtaining diffusion coefficient data known as Gouy interferometry was employed to measure diffusion coefficients in undersaturated and supersaturated aqueous urea solutions at 25°C. The use of laser light as a monochromatic light source in the interferometer greatly simplified the procedure for obtaining diffusivity data from the interferometer. A novel design of a real image camera was employed to record the interferometric data. Values obtained from the interferometric data for low concentration (0–4 molar) aqueous urea solutions were within ±5% of literature values. The diffusion coefficient was found to decrease linearly with increasing concentration up to the saturation point of the aqueous urea solutions, and to decrease drastically with increasing concentration in the supersaturated region. This behavior is similar to that observed in liquid-liquid systems near the consolute point (Cussler, 1980). It is speculated that this phenomenon is a result of molecular aggregation of the urea molecules in supersaturated aqueous solutions. Very little experimental data have previously been obtained in the supersaturated region due to crystallization problems. Supersaturated diffusion coefficient data are important in the study and design of crystallization processes. The solid-solute-liquid solvent binary systems urea-water and sucrose-water were modeled as a saturated solution solute-liquid solvent system in order to test various concentration dependent diffusion relationships. Two of these relationships, the Vignes and Leffler-Cullinan equations, showed improved correlation with experimentally determined diffusivity data for aqueous urea and aqueous sucrose solutions at undersaturated conditions.

Journal ArticleDOI
TL;DR: In this article, a physical interpretation of the experimental results is advanced, within the frame of reference of the radiation-pressure theory of thermal diffusion, and current ideas on the structure of electrolytic solutions can be fruitfully used within the proposed approach, to describe some important thermodynamic parameters in terms of molecular organization in the liquid phase.
Abstract: Thermal diffusion of sodium chloride and potassium chloride aqueous solutions exhibits anomalous behavior in solute-specific concentration and temperature ranges. An accurate analysis is presented showing that these results are not instrumental artifacts. A physical interpretation of the experimental results is advanced, within the frame of reference of the radiation-pressure theory of thermal diffusion. Current ideas on the structure of electrolytic solutions can be fruitfully used, within the proposed approach, to describe some important thermodynamic parameters in terms of molecular organization in the liquid phase. 7 figures, 2 tables.

Journal ArticleDOI
TL;DR: In this article, experimental data on the thermal conductivity, specific heat, and thermal diffusivity of quartz glass over the temperature range 60-1100°K are presented. And the generalized empirical equations describing the temperature dependence of these thermophysical parameters were presented.
Abstract: Available experimental data on the thermal conductivity, specific heat, and thermal diffusivity of quartz glass over the temperature range 60–1100°K are generalized Empirical equations describing the temperature dependence of these thermophysical parameters are presented