Showing papers on "Thermal diffusivity published in 1974"
TL;DR: In this paper, it was shown that the description of thermal convection by blood is inconsistent in this equation, and that results are in error by the same order of magnitude as the convective energy transport itself.
Abstract: The widely used bio-heat transfer equation is examined regarding its term describing the thermal effects of blood perfusion. It is demonstrated, both by physical arguments and numerical results, that the description of thermal convection by blood is inconsistent in this equation, and that results are in error by the same order of magnitude as the convective energy transport itself.
241 citations
220 citations
TL;DR: For the activated carbon particles (of the same size) which have a bidisperse pore-volume distribution (pore diameter range 15 to 104A), the effect of intraparticle diffusion was much less important and separation of the external diffusion resistance was not possible as mentioned in this paper.
Abstract: Rates were measured at 25°C for the adsorption of benzaldehyde from an aqueous solution into particles of Amberlite, or activated carbon, suspended in the solution. The data for monodisperse, Amberlite particles (mean pore radius = 50A) showed significant intraparticle diffusion resistance over the entire particle size range 200 to 900 microns (diameter). Intraparticle diffusivities were larger (tortuosity factor ∼ 0.35) than expected from pore-volume diffusion in the liquid-filled pores.
For the activated carbon particles (of the same size) which have a bidisperse pore-volume distribution (pore diameter range 15 to 104A), the effect of intraparticle diffusion was much less important and separation of the external diffusion resistance to obtain a precise value of the intraparticle diffusivity was not possible. However, De values are larger than for Amberlite and much greater than the molecular diffusivity of benzaldehyde in liquid-filled pores. The unusually high intraparticle diffusivity seems most likely to be due to interpreting dynamic adsorption data for a bidisperse porous particle with a theory involving but one diffusivity.
111 citations
TL;DR: In this paper, it was pointed out that sunspots represent a disruption in the uniform flow of heat through the convective zone and the basic sunspot structure is determined by the energy transport equation.
Abstract: It is pointed out that sunspots represent a disruption in the uniform flow of heat through the convective zone. The basic sunspot structure is, therefore, determined by the energy transport equation. The solutions of this equation for the case of stochastic heat transport are examined. It is concluded that a sunspot is basically a region of enhanced, rather than inhibited, energy transport and emissivity. The heat flow equations are discussed and attention is given to the shallow depth of the sunspot phenomenon. The sunspot is seen as a heat engine of high efficiency which converts most of the heat flux into hydromagnetic waves.
90 citations
TL;DR: This article showed that the thermal lens effect in a binary liquid mixture is noticeably larger than in its two pure constituents and interpreted the anomalous effect observed in the mixture as a consequence of the buildup of thermally induced concentration gradients (Soret effect).
Abstract: We present data showing that the thermal lens effect in a binary liquid mixture is noticeably larger than in its two pure constituents. The anomalous effect observed in the mixture is interpreted as a consequence of the buildup of thermally induced concentration gradients (Soret effect). We suggest that the thermal lens technique could be exploited for determining the thermal diffusion ratio kT in binary liquid mixtures.
88 citations
01 Jan 1974
64 citations
01 Feb 1974
TL;DR: In this paper, a broad theoretical and experimental investigation of retention in thermal field-flow fractionation is reported, and new equations are developed to account for the distortion of the flow profile caused by a variable viscosity.
Abstract: A broad theoretical and experimental investigation of retention in thermal field-flow fractionation is reported here. Equations connecting retention parameters with underlying thermal diffusion constants are reviewed, and new equations are developed to account for the distortion of the flow profile caused by a variable viscosity. Parameters investigated experimentally include channel width, solute molecular weight, channel temperature drop, cold-wall temperature, sample size, and solvent effects. All but the last two of these experimental studies showed good conformity with theoretical predictions. No theory exists for the prediction of sample-size or solvent effects. With regard to the latter, experimental results show that a variety of organic solvents are very effective, at roughly equal levels, in providing retention, while aqueous solvents are generally ineffective.
62 citations
61 citations
TL;DR: In this article, thermogravimetry (TG) was used for determining solubility, diffusivity, thermodynamic properties, and kinetic parameters of 12 selected organic liquid solvents in polyurethane membrane.
51 citations
TL;DR: In this article, the authors made measurements for nitrogen adsorption on molecular-sieving carbons at 60, 100 and 150°C for several different nitrogen surface coverages.
Abstract: Chromatographic measurements were made for nitrogen adsorption on molecular-sieving carbons at 60, 100 and 150°C for several different nitrogen surface coverages. Apparent adsorption equilibrium constants were determined from the retention times of the peaks for different concentrations, and the adsorption equilibrium isotherms were then determined. The peak width gave the intra-microparticle diffusivity where the effects of all the other possible transport processes were taken into account. The strong dependence of the diffusivity on the amount adsorbed was explained in terms of chemical potential gradient as a driving force of the diffusion.
49 citations
TL;DR: In this paper, the authors derived the effective thermal conductivity characterizing macroscopic heat transfer in a granular material consisting of a continuous medium containing spherical granules of other substances under the assumption that the spatial distribution of granules is random.
IBM1
TL;DR: In this paper, the Fisher-type approximations for an equiaxial and perfectly textured grain structure were used to obtain the diffusion profiles for grain-boundary electromigration.
Abstract: It is demonstrated that with proper analysis of the diffusion profiles, the effective charge and diffusivity for grain‐boundary electromigration can be separately measured. Electromigration profiles are analyzed based on Fisher‐type approximations for an equiaxial and perfectly textured grain structure. Electromigration profiles were obtained for Cu in Al at 255°C by measuring the spreading of a Cu cross‐stripe subject to a direct current; the results were checked by annealing experiments performed under similar conditions. Cu was observed to migrate in the direction of electron flow. Results obtained from analysis of the anode and annealing profiles are −16.8±1.2 for the effective charge and (1.75±0.12) × 10−14 cm3/sec for the diffusivity parameter αDbδ. The over‐all consistency of the results is better than 5%. Whipple analysis gives a more exact value of (2.74±0.16) × 10−14 cm3/sec for αDbδ.
TL;DR: In this paper, a numerical calculation of crystallinity and temperature within a running filament is described, and the results are compared with those obtained by a simpler calculation in which the radial temperature distribution is neglected.
Abstract: Crystallization during melt spinning is studied as an example of the nonisothermal crystallization of polymers. The following equation is derived, taking the temperature distribution within a filament into consideration:
where T = temperature, X = crystallinity, κ = thermal diffusivity, V = velocity, ΔH = heat of crystallization, and Cp = specific heat at constant pressure. The assumptions and the procedure for a numerical calculation of crystallinity and temperature within a running filament are described, and some results of calculation are illustrated. The results are compared with those obtained by a simpler calculation in which the radial temperature distribution is neglected. The simpler method proved useful in connection with x-ray measurements.
TL;DR: The diffusivities of hydrogen and glyceryl trioleate in cottonseed oil were determined at different iodine values as mentioned in this paper, and the diffusivity of hydrogen was shown to be ca. 100 times as great as that of the glycery ltoleate.
Abstract: The diffusivities of hydrogen and glyceryl trioleate in cottonseed oil were determined at different iodine values. The diffusivity of hydrogen was shown to be ca. 100 times as great as that of the glyceryl trioleate. The diffusivities were shown to be dependent upon the iodine values. This influence could be explained, at least in the case of the glyceryl trioleate diffusion, by the difference of the viscosity of the oil. A separate determination of the solubility of hydrogen in the oil was a necessary part of the diffusivity determination.
TL;DR: In this paper, a technique for measuring the absolute thermal diffusivity along with the relative specific heat is introduced which is readily adaptable to a wide variety of applications and is shown to mirror the specific heat, with no evidence for anomalies in the thermal conductivities.
TL;DR: In this article, the authors used the wetted sphere technique for the measurement of diffusivity of gases in polymeric solutions under flow conditions and showed that gas absorption from a stress-free interface may not be a sensitive technique of studying shear rate dependence of D.
TL;DR: In this article, the thermal diffusivities along three crystallographic orientations are measured for olivine and pyroxene up to 1250K. The results show that the anisotropy amounts to about 70%.
Abstract: The thermal diffusivities along three crystallographic orientations are measured for olivine and pyroxene up to 1250K. The result shows that the anisotropy amounts to about 70%. The anisotropy is attributed mostly to anisotropy of mean free path of phonon. The anisotropy of thermal conductivity and thermal diffusivity in dunite is measured and is discussed on the basis of preferred orientation and the anisotropy of constituent minerals.
TL;DR: In this article, the porosity correction term is shown to be temperature-dependent, and it is suggested that the deviation from linearity at high temperatures is due to an electronic contribution to the total thermal conductivity.
Abstract: Measurements have been made using a flash thermal diffusivity technique from 550 to 2500 K on a range of well-characterized materials. Data are reported on specimens of five different porosity levels, samples in which porosity has been redistributed, and specimens, initially of two different porosity levels, oxidized to three different hyperstoichiometries. The data are discussed in the light of current theories, and it is shown that the porosity correction term is temperature-dependent. The conductivity λP at any porosity P over the temperature (T) range 500-1600 K is given by λP (W m−1 K−1) = [00433+0355P + (201+147P) × 10−4T]−1. This temperature-dependent porosity correction is shown to be related to total porosity, and it is suggested that this is due to additional vacancy scattering. An expression is derived for the additional phonon scattering due to interstitial oxygen atoms up to small hyperstoichiometry levels. Finally, the deviation from linearity at high temperatures is shown to be due to an electronic contribution to the total thermal conductivity.
TL;DR: The effect of slow crack growth on the thermal-shock resistance of an Na2O-CaO-SiO2 glass was studied in this paper, where the critical quenching temperature difference, ΔTc, of circular rods quenched in water from known crack velocity data was calculated.
Abstract: The effect of slow crack growth on the thermal-shock resistance of an Na2O-CaO-SiO2 glass was studied. An analytic and numerical technique was developed to calculate the critical quenching temperature difference, ΔTc, of circular rods quenched in water from known crack velocity data. For rods of a specific radius and crack depth, ΔTc, was calculated to be 147°C, in favorable correspondence with experimentally observed values of 155° to 160°C. In the absence of crack growth, ΔTc was estimated to be 238°C, well in excess of the observed value and indicative of the significant effect of slow crack growth on thermal-stress resistance. It is also shown that crack growth significantly extends the time-to-failure to a value much greater than the time of maximum thermal stress. A form of subcritical crack instability is predicted at stress intensity factors well below the critical stress intensity factor, at which catastrophic failure becomes inevitable over the duration of the transient thermal stress. It is suggested that, when all other factors are equal, the effect of slow crack growth on thermal-stress resistance can be minimized by maximizing thermal diffusivity. It is also argued that surface-compression strengthening will be more effective than reduction in flaw size in increasing thermal-stress resistance. Recommendations are made for the design and selection of brittle materials subjected to thermal stress in stress-corrosive environments.
TL;DR: In this paper, an approach to study diffusion in liquid crystals is described in which the optically observable textural changes in a nematic phase caused by a cholesteric diffusant gives direct visualization of the concentration gradient.
Abstract: A new approach to studying diffusion in liquid crystals is described in which the optically observable textural changes in a nematic phase caused by a cholesteric diffusant gives direct visualization of the concentration gradient. Utilizing either homeotropic of homogeneous alignments under different boundary conditions, and with and without an applied magnetic field, the parallel and perpendicular components of the diffusivity have been determined for a cholesteryl ester diffusing into N‐(p ‐methoxybenzylidene)‐p ‐n ‐butylaniline as a function of temperature. The diffusion coefficients in the isotropic phase can also be determined by annealing at a high temperature and quenching to room temperature, whereupon the cholesteric texture is again developed. Values of the diffusion coefficients and the activation energies of the diffusion process are discussed and compared to other available data.
TL;DR: In this article, the effective diffusivity decreases with decreased permeability of the rock for gas-phase diffusion and for helium dissolved in water, and a similar correlation is obtained for increased threshold-displacement pressure for nitrogen displacing water from the rock.
Abstract: Diffusion measurements made for helium through porous cores including caprocks show that the effective diffusivity decreases with decreased permeability of the rock for gas-phase diffusion and for helium dissolved in water. A similar correlation is obtained of decreased diffusivity for increased threshold-displacement pressure for nitrogen displacing water from the rock. These correlations verify that parameters which indicate constrictions in the interstices of the rock also restrict diffusion.
TL;DR: In this paper, a technique is described which permits the accurate measurement of heat capacities to very low temperatures without the use of a heat switch, and the specific heat of Cu, with and without hydrogen impurities, has been measured in the temperature range 0.04-1 K.
Abstract: A technique is described which permits the accurate measurement of heat capacities to very low temperatures without the use of a heat switch. As a test of this technique the specific heat of Cu, with and without hydrogen impurities, has been measured in the temperature range 0.04–1 K. The presence of hydrogen increases the specific heat by ≈ 1% as has been reported previously at higher temperatures. Above 0.3 K the data for hydrogen‐free copper are in good agreement with the copper reference equation. At lower temperatures there is an additional contribution to the heat capacity which may be associated with oxygen impurities.
TL;DR: In this paper, a detailed discussion of simple non-compound-forming systems is given, in particular to the Si-Al, Ge-Al and Si-Au systems.
Abstract: Solid metal-semiconductor interfaces often undergo chemical reaction at rather low temperatures, in some cases not much above room temperature. After some general discussion of these reactions, more detailed consideration is given to simple noncompound-forming systems, and, in particular, to the Si-Al, Ge-Al, and Si-Au systems. Diffusive transport of Si or Ge in these solid metallizations is very rapid, though the converse process, diffusion of metal in solid Si or Ge, is usually so slow as to be negligible. The interface reaction itself is less well understood but is becoming controllable in intrinsically favorable cases like Ge-Al and in other cases by more sophisticated means.
TL;DR: In this article, it was shown that the strong concentration dependence of the heat of transport Q+ found by Lohnert and Fromm in the Ta-O system appeared in the Nb-N system, too, and could be described by the following empirical formula Q + = − 2,4 c kcal at.
TL;DR: In this article, a solution for unsteady state concentration profiles in an infinitely long composite cylinder resulting from a step-change in concentration in a large reservoir surrounding the cylinder is given.
Abstract: A solution is given for unsteady state concentration profiles in an infinitely long composite cylinder resulting from a step-change in concentration in a large reservoir surrounding the cylinder. The composite cylinder consists of an inner cylinder with diffusivity D1 surrounded by a permeable tube with diffusivity D2 and has interfacial mass transfer resistances at the cylinder-tube and tube-reservoir interfaces. Numerical values are given for the first eight roots and various coefficients of the solution for physical properties typical of tubular (hollow fiber) membranes. These results can be used in the analysis of data from unsteady state mass transfer experiments to determine the permeability of homogeneous tubular membranes. A simple, approximate method for data analysis is suggested for the rapid estimation of the permeability of both homogeneous and asymmetric (skinned) tubular membranes.
TL;DR: The thermal diffusivity and electrical resistivity of LaB6 have been measured at high temperatures from 1300 to 2000 K as discussed by the authors, and an analysis of the data indicates that the Wiedemann-Franz law is not obeyed in this temperature range.
Abstract: The thermal diffusivity and the electrical resistivity of LaB6 have been measured at high temperatures from 1300 to 2000 K. An analysis of the data indicates that the Wiedemann-Franz law is not obeyed in this temperature range. The discrepancy arises because of the relatively high lattice thermal conductivity. The observed lattice conductivity is 3.5*10-2 cal cm-1 s-1 K-1 at 1300 K, which is in good agreement with the calculated value.
TL;DR: In this article, de Gruyter et al. presented measurements of the Soret coefficient by means of a flowing cell technique for disulfide-3 methylpentane and for the three associated solutions: carbon tetrachloride-ethanol, carbon TTRACLIDE-isopropanol, and water-ISOPropanol.
Abstract: In this paper we present measurements of the Soret coefficient (D'/D) by means of a flowing cell technique for disulfide-3 methylpentane and for the three associated solutions: carbon tetrachloride-ethanol, carbon tetrachloride-isopropanol and water-isopropanol. © 1974, Walter de Gruyter. All rights reserved.