Showing papers on "Thermal diffusivity published in 1999"
TL;DR: A phase-field model (PFM) for solidification in binary alloys, which is found from the phase- field model for apure material by direct comparison of the variables for a pure material solidification and alloy solidification, is presented.
Abstract: We present a phase-field model (PFM) for solidification in binary alloys, which is found from the phase-field model for a pure material by direct comparison of the variables for a pure material solidification and alloy solidification. The model appears to be equivalent with the Wheeler-Boettinger-McFadden (WBM) model [A.A. Wheeler, W. J. Boettinger, and G. B. McFadden, Phys. Rev. A 45, 7424 (1992)], but has a different definition of the free energy density for interfacial region. An extra potential originated from the free energy density definition in the WBM model disappears in this model. At a dilute solution limit, the model is reduced to the Tiaden et al. model [Physica D 115, 73 (1998)] for a binary alloy. A relationship between the phase-field mobility and the interface kinetics coefficient is derived at a thin-interface limit condition under an assumption of negligible diffusivity in the solid phase. For a dilute alloy, a steady-state solution of the concentration profile across the diffuse interface is obtained as a function of the interface velocity and the resultant partition coefficient is compared with the previous solute trapping model. For one dimensional steady-state solidification, where the classical sharp-interface model is exactly soluble, we perform numerical simulations of the phase-field model: At low interface velocity, the simulated results from the thin-interface PFM are in excellent agreement with the exact solutions. As the partition coefficient becomes close to unit at high interface velocities, whereas, the sharp-interface PFM yields the correct answer.
804 citations
TL;DR: In this paper, the level-set approach is applied to a regime of premixed turbulent combustion where the Kolmogorov scale is smaller than the flame thickness, called the thin reaction zones regime, characterized by the condition that small eddies can penetrate into the preheat zone, but not into the reaction zone.
Abstract: The level-set approach is applied to a regime of premixed turbulent combustion where the Kolmogorov scale is smaller than the flame thickness. This regime is called the thin reaction zones regime. It is characterized by the condition that small eddies can penetrate into the preheat zone, but not into the reaction zone.By considering the iso-scalar surface of the deficient-species mass fraction Y immediately ahead of the reaction zone a field equation for the scalar quantity G(x, t) is derived, which describes the location of the thin reaction zone. It resembles the level-set equation used in the corrugated flamelet regime, but the resulting propagation velocity s*L normal to the front is a fluctuating quantity and the curvature term is multiplied by the diffusivity of the deficient species rather than the Markstein diffusivity. It is shown that in the thin reaction zones regime diffusive effects are dominant and the contribution of s*L to the solution of the level-set equation is small.In order to model turbulent premixed combustion an equation is used that contains only the leading-order terms of both regimes, the previously analysed corrugated flamelets regime and the thin reaction zones regime. That equation accounts for non-constant density but not for gas expansion effects within the flame front which are important in the corrugated flamelets regime. By splitting G into a mean and a fluctuation, equations for the Favre mean [Gtilde]and the variance [Gtilde]″2 are derived. These quantities describe the mean flame position and the turbulent flame brush thickness, respectively. The equation for [Gtilde]″2 is closed by considering two-point statistics. Scaling arguments are then used to derive a model equation for the flame surface area ratio [rhotilde]. The balance between production, kinematic restoration and dissipation in this equation leads to a quadratic equation for the turbulent burning velocity. Its solution shows the ‘bending’ behaviour of the turbulent to laminar burning velocity ratio sT/sL, plotted as a function of v′/sL. It is shown that the bending results from the transition from the corrugated amelets to the thin reaction zones regimes. This is equivalent to a transition from Damkohler's large-scale to his small-scale turbulence regime.
728 citations
TL;DR: In this article, the thin layer drying characteristics of hazelnuts during roasting were described for a temperature range of 100-160°C, using five semi-theoretical and two empirical thin layer models.
445 citations
TL;DR: In this paper, the results of a comparative numerical investigation on packed bed thermal models suitable for sensible and latent heat thermal storage systems were presented. But the results obtained were compared, analysed and discussed.
256 citations
TL;DR: In this paper, a mathematical model is established for chloride penetration in saturated concrete, which takes into account various influential parameters such as water-to-cement ratio, curing time, types of cement, and aggregate content.
Abstract: A mathematical model is established for chloride penetration in saturated concrete. The model takes into account various influential parameters such as water-to-cement ratio, curing time, types of cement, and aggregate content. Two material models are developed for binding capacity and chloride diffusivity, which have a dominant effect on the chloride diffusion process. The chloride binding capacity is modeled by means of the chloride adsorption isotherm. The chloride diffusivity is modeled by a composite material theory in which concrete is considered as a two-phase material with the cement paste as one phase and the aggregate as another. To take into account the effect of aggregate content, the three-phase model for diffusivity of a two-phase composite developed by Christensen is used. The diffusivity for cement paste is characterized by the Kozeny-Carman model as modified by Martys et al. The influences of temperature and chloride ion concentration are also handled in the model. The model prediction agrees quite well with available test results.
245 citations
TL;DR: In this paper, an acoustic boundary layer appears near the droplet surface resulting in an acoustic streaming, and the authors derived the time and surface average of the Sherwood and Nusselt number distributions over the surface of a pure liquid droplet.
Abstract: The rate of heat and mass transfer at the surface of acoustically levitated pure liquid droplets is predicted theoretically for the case where an acoustic boundary layer appears near the droplet surface resulting in an acoustic streaming. The theory is based on the computation of the acoustic field and squeezed droplet shape by means of the boundary element method developed in Yarin, Pfaffenlehner & Tropea (1998). Given the acoustic field around the levitated droplet, the acoustic streaming near the droplet surface was calculated. This allowed calculation of the Sherwood and Nusselt number distributions over the droplet surface, as well as their average values. Then, the mass balance was used to calculate the evolution of the equivalent droplet radius in time. The theory is applicable to droplets of arbitrary size relative to the sound wavelength λ, including those of the order of λ, when the compressible character of the gas flow is important. Also, the deformation of the droplets by the acoustic field is accounted for, as well as a displacement of the droplet centre from the pressure node. The effect of the internal circulation of liquid in the droplet sustained by the acoustic streaming in the gas is estimated. The distribution of the time-average heat and mass transfer rate over the droplet surface is found to have a maximum at the droplet equator and minima at its poles. The time and surface average of the Sherwood number was shown to be described by the expression Sh = KB/√ω[Dscr ]0, where B = A0e/(ρ0c0) is a scale of the velocity in the sound wave (A0e is the amplitude of the incident sound wave, ρ0 is the unperturbed air density, c0 is the sound velocity in air, ω is the angular frequency in the ultrasonic range, [Dscr ]0 is the mass diffusion coefficient of liquid vapour in air, which should be replaced by the thermal diffusivity of air in the computation of the Nusselt number). The coefficient K depends on the governing parameters (the acoustic field, the liquid properties), as well as on the current equivalent droplet radius a.For small spherical droplets with a[Lt ]λ, K = (45/4π)1/2 = 1.89, if A0e is found from the sound pressure level (SPL) defined using A0e. On the other hand, if A0e is found from the same value of the SPL, but defined using the root-mean-square pressure amplitude (prms = A0e/√2), then Sh = KrmsBrms/
√ω[Dscr ]0, with Brms = √2B and Krms = K/√2 = 1.336. For large droplets squeezed significantly by the acoustic field, K appears always to be greater than 1.89. The evolution of an evaporating droplet in time is predicted and compared with the present experiments and existing data from the literature. The agreement is found to be rather good.We also study and discuss the effect of an additional blowing (a gas jet impinging on a droplet) on the evaporation rate, as well as the enrichment of gas at the outer boundary of the acoustic bondary layer by liquid vapour. We show that, even at relatively high rates of blowing, the droplet evaporation is still governed by the acoustic streaming in the relatively strong acoustic fields we use. This makes it impossible to study forced convective heat and mass transfer under the present conditions using droplets levitated in strong acoustic fields.
238 citations
TL;DR: In this article, a model based on the ratio between heat conduction in parallel and serial layers of gas, liquid, and solid phases was proposed to explain the behavior of the effective thermal conductivity of Swedish wood.
Abstract: Transient simultaneous measurements of thermal conductivity and diffusivity of Swedish wood have been performed with the plane source technique on oven-dry hardwood (birch) samples at room temperature and at 100 °C. The influences of temperature, density, porosity and anisotropy on thermal conduction were investigated. The measurements were done in longitudinal (parallel to the grain) and transverse (intermediate between radial and tangential) directions. As the temperature increased from 20 to 100 °C, the thermal conductivity of each sample increased slightly for both longitudinal and transverse directions. The effect of density and porosity on the thermal conductivity may be related to the presence of other scattering mechanisms such as voids and cell boundaries. It seems that the dominant mechanism of heat transfer across the cell lumina in these types of wood is the heat conduction through the voids. An attempt was made to explain the behaviour of the effective thermal conductivity by adopting a model based on the ratio between heat conduction in parallel and serial layers of gas, liquid, and solid phases.
237 citations
TL;DR: The ionic contributions to the electrical conductivity are based on a differential effective medium approach and the influence of the temperature and the presence of a second immiscible and nonwetting phase is also considered in this model.
215 citations
TL;DR: Simulation results are consistent with the predictions of the mode-coupling theory for the dynamics of weakly supercooled liquids, strongly supporting the hypothesis that the apparent divergences of dynamic properties observed experimentally may be independent of a possible thermodynamic singularity at low temperature.
Abstract: We present molecular dynamics simulations of the extended simple-point-charge model of water to probe the dynamic properties at temperatures from 350 K down to 190 K and pressures from 2.5 GPa ~25 kbar! down to 2300 MPa (23 kbar). We compare our results with those obtained experimentally, both of which show a diffusivity maximum as a function of pressure. We find that our simulation results are consistent with the predictions of the mode-coupling theory for the dynamics of weakly supercooled liquids—strongly supporting the hypothesis that the apparent divergences of dynamic properties observed experimentally may be independent of a possible thermodynamic singularity at low temperature. The dramatic change in water’s dynamic and structural properties as a function of pressure allows us to confirm the predictions of MCT over a much broader range of the von Schweidler exponent values than has been studied for simple atomic liquids. We also show how structural changes are reflected in the wave-vector dependence of dynamic properties of the liquid along a path of nearly constant diffusivity. For temperatures below the crossover temperature of MCT ~where the predictions of MCT are expected to fail!, we find tentative evidence for a crossover of the temperature dependence of the diffusivity from power-law to Arrhenius behavior, with an activation energy typical of a strong liquid. @S1063-651X~99!11712-4#
201 citations
TL;DR: In this article, a TDR probe was developed to simultaneously measure volumetric water content and thermal properties in surface soil, and the results showed that the probe determined θ accurately and measured σ values of saturated soil correlated well with values determined by a four-electrode probe.
Abstract: Hydraulic and thermal regimes are coupled in surface soil. Accurate measurement of soil volumetric water content (θ) and thermal properties will improve our understanding of the hydraulic and thermal regimes. A thermo-time domain reflectometry (TDR) probe was developed to simultaneously measure θ, bulk electrical conductivity (σ), thermal conductivity (λ), heat capacity (ρ c ), and thermal diffusivity (α). Time domain reflectometry was used to measure θ and σ, and the dual-probe heat pulse (DPHP) method was used to determine λ, ρ s , and α. Laboratory tests on two soils showed that the probe determined θ accurately and the measured σ values of saturated soil correlated well with values determined by a four-electrode probe. Measurements in agar-immobilized water produced values of λ and ρ c that closely corresponded with standard values of these properties for water, an indication of the sensor's functionality in other media. Soil thermal properties as a function of θ also are presented. The results of these laboratory tests suggest that the thermo-TDR probe can be a valuable tool for simultaneously monitoring θ, σ, and soil thermal properties.
178 citations
TL;DR: In this paper, the authors present results from a sim ple moisture absorption measurement that led to a good estimate of the moisture diffusivity of building materials, based on measurements on a sample of spruce.
Abstract: Moisture diffusivity is a transport property that is frequently used in the hygrothermal analysis of building envelope components. This property is de pendent on the local moisture content. The experiments that lead to the detailed in formation on the dependence of diffusivity on moisture content are often very so phisticated. However, two recent exercises, as a part of the activities of an International Energy Agency Annex, have shown that a correct estimate of the mag nitude of the moisture diffusivity can provide useful information with regard to its application in hygrothermal analysis. This technical note presents results from a sim ple moisture absorption measurement that led to a good estimate of the moisture diffusivity of building materials. Results from measurements on a sample of spruce are presented.
TL;DR: In this article, the thermal diffusivity and heat capacity of uranium dioxide have been measured from 500 to 2900 K with an advanced laser-flash technique by means of an accurate numerical fitting of the experimental thermograms.
Abstract: The thermal diffusivity and heat capacity of uranium dioxide have been measured from 500 to 2900 K with an advanced laser-flash technique. These two quantities were determined simultaneously by means of an accurate numerical fitting of the experimental thermograms. At high temperatures the precision of the method used is much better than that associated with conventional laser-flash measurements. It was found that the heat capacity continues to increase even at temperatures above the expected lambda transition (2670 K). The inverse of the thermal diffusivity increases linearly with temperature up to 2600 K, whilst at higher temperatures the slope markedly decreases. A new expression for the thermal conductivity as a function of temperature is proposed, which is corroborated by some theoretical considerations on the underlying heat transport mechanisms.
TL;DR: In this paper, a simple alternative which estimates the diffusivity from sorptivity and porosity measurements is presented for an assumed exponential dependence of diffusivities on water saturation.
Abstract: Uptake of water (and therefore ions) by unsaturated, hardened concrete may be characterised by the sorptivity. This is a simple parameter to determine and is increasingly being used as a measure of concrete resistance to exposure in aggressive environments. The complete process is described by a nonlinear diffusion equation, with the hydraulic diffusivity a strongly nonlinear function of the degree of saturation of the concrete. Accurate analytical approximations to the solution of this equation, as well as numerical solutions for general conditions, exist when the diffusivity function is known. Unfortunately, it is not an easy function to determine, requiring accurate information on the water penetration profile. A simple alternative which estimates the diffusivity from sorptivity and porosity measurements is presented for an assumed exponential dependence of diffusivity on water saturation. Predicted water penetration profiles corresponding to this estimated diffusivity are shown to be accurate by comparison with published experimental results.
TL;DR: In this paper, the role of the relevant process parameters has been investigated experimentally (the flow rate through the cell, the feed initial concentration, the type of membrane, the air gap thickness, etc.).
TL;DR: In this article, a non-equilibrium method for calculating transport coefficients is presented, which reverses the experimental cause-and-effect picture, e.g. for the calculation of viscosities: the effect, the momentum flux or stress, is imposed, whereas the cause, the velocity gradient or shear rates, is obtained from the simulation.
TL;DR: In this paper, a two-dimensional model of the cathode compartment of a polymer electrolyte fuel cell has been developed, based on continuity equations for concentrations of the gases and Poisson's equations for potentials of membrane and carbon phase coupled by Tafel relation for reaction kinetics.
Abstract: A two‐dimensional model of the cathode compartment of a polymer electrolyte fuel cell has been developed. The existence of gas channels in the current collector is taken into account. The model is based on continuity equations for concentrations of the gases and Poisson's equations for potentials of membrane and carbon phase, coupled by Tafel relation for reaction kinetics. Stefan‐Maxwell and Knudsen diffusion of gases are taken into account. The simulations were performed for high and low values of carbon phase conductivity. The results revealed (i) for a low value of carbon phase conductivity, a "dead zone" in the active layer in front of the gas channel is formed, where the reaction rate is small. One may remove catalyst from this zone without significant loss in cell performance. (ii) For a high carbon phase conductivity value, such a zone is absent, but removal of the catalyst from the same part of the active layer forces the reaction to proceed more rapidly in the remaining parts, with only marginal losses in performance. This conclusion is valid for high diffusivity of oxygen. For low diffusivity, dead zones are formed in front of the current collector, so that catalyst can be removed from these zones. The results, thus, show the possibilities for a considerable reduction of the amount of catalyst. © 1999 The Electrochemical Society. All rights reserved.
TL;DR: Using molecular dynamics with classical interaction potentials, the authors in this article presented calculations of thermal conductivity and heat transport in crystals and glasses, and investigated the spreading of energy and temperature over the configurations.
Abstract: Using molecular dynamics (MD) with classical interaction potentials we present calculations of thermal conductivity and heat transport in crystals and glasses. Inducing shock waves and heat pulses into the systems we study the spreading of energy and temperature over the configurations. Phonon decay is investigated by exciting single modes in the structures and monitoring the time evolution of the amplitude using MD in a microcanonical ensemble. As examples, crystalline and amorphous modifications of Selenium and $\rm{SiO_2}$ are considered.
TL;DR: In this paper, a simple but soil-type-dependent power function D s /D 0 (e) model was proposed to describe and predict gas diffusivity in undisturbed soil.
Abstract: Accurate description of gas diffusivity (ratio of gas diffusion coefficients in soil and free air, D s /D 0 ) in undisturbed soils is a prerequisite for predicting in situ transport and fate of volatile organic chemicals and greenhouse gases. Reference point gas diffusivities (R p ) in completely dry soil were estimated for 20 undisturbed soils by assuming a power function relation between gas diffusivity and air-filled porosity (e). Among the classical gas diffusivity models, the Buckingham (1904) expression, equal to the soil total porosity squared, best described R p . Inasmuch as our previous works (Parts III, VII, VIII) implied a soil-type dependency of D s /D 0 (e) in undisturbed soils, the Buckingham R p expression was inserted in two soil- type-dependent D s /D 0 (e) models. One D s /D 0 (e) model is a function of pore-size distribution (the Campbell water retention parameter used in a modified Burdine capillary tube model), and the other is a calibrated, empirical function of soil texture (silt + sand fraction). Both the Buckingham-Burdine-Campbell (BBC) and the Buckingham/soil texture-based D s /D 0 (e) models described well the observed soil type effects on gas diffusivity and gave improved predictions compared with soil type independent models when tested against an independent data set for six undisturbed surface soils (11-46% clay). This study emphasizes that simple but soil-type-dependent power function D s /D 0 (e) models can adequately describe and predict gas diffusivity in undisturbed soil. We recommend the new BBC model as basis for modeling gas transport and reactions in undisturbed soil systems.
TL;DR: In this paper, a set of yttria partially stabilized zirconia coatings with different thickness was deposited on flat nickel-base alloy coupons by air plasma spray (APS) under uncontrolled temperature conditions.
Abstract: A set of yttria partially stabilized zirconia coatings with different thickness was deposited on flat nickel-base alloy coupons by air plasma spray (APS) under uncontrolled temperature conditions. In this way, the length of the spraying process (and consequently the coating thickness) had a direct effect on phase composition as well as on the thermal properties of the material. In particular, both the monoclinic phase percentage and thermal diffusivity increased considerably with the thickness. Because this trend was observed together with a slight but clearly visible increase in the total porosity, the interpretation of the results was not straightforward, but required a detailed discussion of the thermal transport mechanism. Considering the complex microstructure typical of APS coatings and the relevant role of porosity, it was shown how a modest reduction in the fraction of closed pores can account for the observed increase in diffusivity. It was then proposed that the volume change associated with the progressive tetragonal to monoclinic phase transformation can be responsible for the reduction of the closed porosity of lenticular shape oriented parallel to the surface, in spite of the observed increase in the total porosity.
TL;DR: In this paper, the temperature dependence of fluorescence induced by laser radiation of an organic dye is combined with 2D laser Doppler anemometry, in order to measure in the same sample volume simultaneously and instantaneously the temperature and velocity.
Abstract: This paper presents an efficient technique for the characterization of thermal transport properties in turbulent flows. The method is based on the temperature dependence of fluorescence, induced by laser radiation, of an organic dye. The laser-induced fluorescence technique is combined with 2D laser Doppler anemometry, in order to measure in the same sample volume simultaneously and instantaneously the temperature and velocity. The technique is demonstrated on a turbulent heated round jet: the mean and fluctuating dynamic and thermal fields are investigated, and the temperature-velocity cross-correlations are determined in order to characterize the turbulent diffusivity and the turbulent Prandtl number.
TL;DR: In this paper, the diurnal variation of ground heat flux from the corresponding time series measurement of surface soil temperature is computed from a 1D diffusion equation with constant diffusivity parameter.
TL;DR: In this paper, the effects of combined buoyancy forces from mass and thermal diffusion by natural convection flow from a vertical wavy surface have been investigated using the implicit finite difference method.
Abstract: In the present paper, effects of combined buoyancy forces from mass and thermal diffusion by natural convection flow from a vertical wavy surface have been investigated using the implicit finite difference method. Here we have focused our attention on the evolution of the surface shear stress,f″(0), rate of heat transfer,g′(0), and surface concentration gradient,h′(0) with effect of different values of the governing parameters, such as the Schmidt number Sc ranging from 7 to 1500 which are appropriate for different species concentration in water (Pr=7.0), the amplitude of the waviness of the surface ranging from 0.0 to 0.4 and the buoyancy parameter,w, ranging from 0.0 to 1.
TL;DR: In this article, the theory of phonon scattering by vacancies is applied to oxygen vacancies in zirconia and rutile, and it is shown that the theory agrees well with thermal diffusivity reductions in reduced rutsile.
Abstract: The theory of phonon scattering by vacancies is applied to oxygen vacancies in zirconia and rutile. These vacancies are the major source of point defect scattering in stabilized zirconia. It is shown that the theory agrees well with thermal diffusivity reductions in reduced rutile. This lends confidence to the effect of oxygen vacancies on the thermal conductivity of stabilized zirconia, particularly in thermal barrier coatings.
TL;DR: In this paper, the intrinsic gas permeation property of poly(4-vinylpyri-dine) was studied using a free-standing film. But the authors did not consider the effect of gas collision and kinetic diameters.
Abstract: Although poly(4-vinylpyridine) is believed to have good gas permselectivity, the intrinsic gas permeation property is rarely reported in the literature. The objective of this work is to study the the intrinsic gas permeation property of poly(4-vinylpyri- dine) using a free-standing film. Because of its brittleness and strong adhesion with most solid surfaces, a free-standing poly(4-vinylpyridine) film was therefore prepared from casting on a liquid mercury surface. The permeation behavior of He, H2 ,O 2 ,N 2, CH4, and CO2 through the film was tested over a pressure range of 252 to 800 cm Hg at 35°C. The permeability and solubility decrease slightly with an increase in pressure, whereas the diffusivity increases as pressure increases. The pressure-dependent phe- nomenon can be explained using the partial immobilization model and the dual sorption model. An effective gas molecule diameter, which is defined as the square root of the product of gas collision and kinetic diameters, was used to correlate the diffusivity and gas molecule size, and an empirical equation was derived. Solubility is also a strong function of gas physical properties such as critical temperature and Lennard-Jones force constant, which are the measures of gas condensability and molecule interaction, respectively. In general, higher solubility in a polymer is obtained for gases with greater condensability and stronger interaction. Typical gas permeabilities of poly(4- vinylpyridine) measured at 619 cm Hg and 35°C are: 12.36 (He), 12.64 (H2), 3.31 (CO2), 0.84 (O2), 0.14 (CH4), and 0.13 (N2) barrers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2851-2861, 1999
TL;DR: In this article, a poro-visco-plastic (Voigt-type) rheology was proposed to characterize the transition between Newtonian viscous densification and poroplastic deformations.
Abstract: Stressed quartz sand saturated by water can deform by matter transport through the water phase (pressure solution). This process is modeled by a poro-visco-plastic (Voigt-type) rheology. A characteristic time constant characterizes the transition between Newtonian viscous densification and poro-plastic deformations. For short-time scales, the viscous densification is either controlled by interface kinetic or by the diffusivity of the solute Si(OH)4 at the grain contacts. For long-time scales, the poro-plastic rheology corresponds to a thermodynamic equilibrium at the grain contacts.
TL;DR: In this article, the authors investigated the effects of locally enhanced vertical diffusivity over rough bottom topography on the world ocean circulation by use of a coarse-resolution ocean general circulation model.
Abstract: Observations indicate that vertical diffusivity in the deep ocean is considerably enhanced over rough bathymetry and is very small elsewhere. Here we investigate effects of locally enhanced vertical diffusivity over rough bottom topography on the world ocean circulation by use of a coarse resolution ocean general circulation model. Vertical diffusivity is enhanced in the model, taking into account effects of internal tide breaking. For comparison, two cases of an experiment are carried out, where vertical diffusivity increases with depth without horizontal inhomogeneity. Horizontal distribution of deep upwelling is qualitatively different, depending on whether or not vertical diffusivity is horizontally inhomogeneous. Upwelling of Circumpolar Deep Water in the Pacific and Antarctic Bottom Water in the Atlantic is confined where vertical diffusivity is enhanced in the case of horizontally inhomogeneous vertical diffusivity, whereas it is horizontally uniform in the other cases. This difference leads to different three-dimensional structure of the deep circulation.
TL;DR: The chemical diffusivity of BaTiO 3− δ was determined via a conductivity relaxation technique, at elevated temperatures (800≤ T /°C≤1100) as a function of the ambient oxygen partial pressure in the range of 10 −16 ≤ P O 2 /atm≤1 including an n-to p-type transition regime as discussed by the authors.
TL;DR: In this article, the authors used a simple technique and small samples to obtain thermal diffusivity, specific heat capacity, and thermal conductivity, all as a function of sample temperature, for a variety of ingredients used in solid rocket propellants.
Abstract: Using a fairly simple technique and small samples it was possible to obtain thermal diffusivity, specific heat capacity, and thermal conductivity, all as a function of sample temperature, for a variety of ingredients used in solid rocket propellants. The oxidizers AP, ADN, CL20, HMX, RDX, HNF, TNAZ were studied as well as the nonenergetic polymers TeflonTM, HTPB, and polyurethane, energetic binders containing GAP and BAMO and/or NMMO, and actual solid propellants XM39, N5, N12, and SB129.
TL;DR: In this paper, the authors presented an analysis of the stratification decay in thermally stratified vertical cylindrical cool storage systems using a one dimensional conjugate heat conduction model.
15 Mar 1999
TL;DR: Drainage of a partially mobile thin liquid film between two deformed and nondeformed gas bubbles with different radii is studied and the role of the surface viscosity, comparable to that of the Gibbs elasticity, is proposed.
Abstract: Drainage of a partially mobile thin liquid film between two deformed and nondeformed gas bubbles with different radii is studied The lubrication approximation is used to obtain the influence of soluble and insoluble surfactants on the velocity of film thinning in the case of quasi-steady state approach The material properties of the interfaces (surface viscosity, Gibbs elasticity, surface diffusivity, and/or bulk diffusivity) are taken into account In the case of deformed bubbles the influence of the meniscus is illustrated assuming simple approximated shape for the local film thickness Simple analytical solutions for large and small values of the interfacial viscosity, and for deformed and nondeformed bubbles, are derived The correctness of the boundary conditions used in the literature is discussed The numerical analysis of the governing equation shows the region of transition from partially mobile to immobile interfaces Quantitative explanation of the following effects is proposed: (i) increase of the mobility due to increasing bulk and surface diffusivities; (ii) role of the surface viscosity, comparable to that of the Gibbs elasticity; and (iii) significant influence of the meniscus on the film drainage due to the increased hydrodynamic resistance