Showing papers on "Thermal diffusivity published in 1984"

Equilibrium and transport properties of the noble gases and their mixtures at low density

Abstract: The report contains a set of easy‐to‐program expressions for the calculation of the thermodynamic and transport properties of the five noble gases (He, Ne, Ar, Kr, Xe) and of the 26 binary and multicomponent mixtures that can be formed with them. The properties in question are second virial coefficient B, viscosity η, thermal conductivity λ, self‐diffusion and binary diffusion coefficient D, and thermal diffusion factor αT. The calculation of properties is restricted to low densities ( ρ≪B/C) but covers the full range of compositions and a temperature interval extending from absolute zero to the onset of ionization. Owing to the careful theoretical basis on which the algorithm has been erected, all properties are thermodynamically consistent with each other. Reference to a selected set of critically evaluated measurements provides a basis for the estimation of uncertainties. The report contains 54 abbreviated tables of numerical data and 86 deviation plots. It is asserted that the results are comparable to the best measurements that could be performed at present.

Nonequilibrium steady states of stochastic lattice gas models of fast ionic conductors

Abstract: We investigate theoretically and via computer simulation the stationary nonequilibrium states of a stochastic lattice gas under the influence of a uniform external fieldE. The effect of the field is to bias jumps in the field direction and thus produce a current carrying steady state. Simulations on a periodic 30 × 30 square lattice with attractive nearest-neighbor interactions suggest a nonequilibrium phase transition from a disordered phase to an ordered one, similar to the para-to-ferromagnetic transition in equilibriumE=0. At low temperatures and largeE the system segregates into two phases with an interface oriented parallel to the field. The critical temperature is larger than the equilibrium Onsager value atE=0 and increases with the field. For repulsive interactions the usual equilibrium phase transition (ordering on sublattices) is suppressed. We report on conductivity, bulk diffusivity, structure function, etc. in the steady state over a wide range of temperature and electric field. We also present rigorous proofs of the Kubo formula for bulk diffusivity and electrical conductivity and show the positivity of the entropy production for a general class of stochastic lattice gases in a uniform electric field.

Heat Capacity of Reference Materials: Cu and W

Abstract: The CODATA Task Group on Thermophysical Properties is preparing a set of recommended values for the heat capacity, thermal expansion, and transport properties of key solids which are used in calibrating or checking measuring equipment. The present paper surveys selected data on heat capacity at constant pressure Cp of copper from 1 to 1300 K and tungsten from 1 to 3400 K. Selected values are tabulated for Cp and also for heat capacity at constant volume Cv. Interpolating functions are given for Cp.

Self‐diffusivity of network oxygen in vitreous SiO2

Abstract: Secondary ion mass spectrometry was used to profile the interdiffusion of network oxygen in a Si 16O2‐Si 18O2 thin‐film structure. The diffusivity from 1200 to 1400 °C can be described by D=2.6 cm2 s−1 exp (−4.7 eV/kT). The diffusivity values are lower, but with a higher activation energy, than those previously reported in the literature and approach the intrinsic diffusivity uncomplicated by extrinsic gas phase isotope exchange reactions.

Behavior of Alkalies during Diffusive Interaction of Granitic Xenoliths with Basaltic Magma

Abstract: A series of three experiments was made at ∼125°C and 10 kbar in which a 1-gram reservoir of molten oceanic tholeiite was maintained in contact with one end of a 6.5 mm diameter cylinder of partially-molten, fine-grained granite. Detailed microprobe analysis (450 spots total) of the quenched samples revealed progressive basalt/granite interaction as run duration increased from 0.75 to 8 to 24 hours. Interdiffusion of melt components is limited for structure-controlling species such as $$Si^{4+}$$ and $$Al^{3+}$$ and for divalent cations, which all mix over a zone less than 0.5 mm wide in 24 hours at run conditions. In contrast, K and Na are extremely mobile, resulting in considerable uptake of K by the basalt melt and eventual loss of Na from the basalt to the granite by "uphill" diffusion. The chemical diffusivity of K in the basalt can be accurately estimated at $$3 \times 10^{18} cm^{2}/sec$$ for the specific experimental conditions used. Although this value is somewhat lower than previous estimates K o...

The Simultaneous Measurement of Thermal Conductivity, Thermal Diffusivity, and Perfusion in Small Volumes of Tissue

Abstract: An improved technique is presented for the “in-vivo” determination of thermal conductivity, thermal diffusivity, and perfusion using a self-heated spherical thermistor probe. In the presence of flow, solution of the time-dependent, probe-tissue coupled thermal model allows the measurement of “effective” thermal conductivity and “effective” thermal diffusivity, which represent the thermal properties of the perfused tissue. Perfusion can be quantified from both “effective” thermal properties. In the presence of flow, it has been shown that the transient power response does not follow t −1/2 as has been previously assumed. An isolated rat liver preparation has been developed to validate the measurement technique. Radioactive microspheres are used to determine the true perfusion from the total collected hepatic vein flow. Experimental data demonstrates the ability to quantify perfusion in small volumes of tissue.

Thermal, Conductivity, Density, Viscosity, and Prandtl-Numbers of Ethylene Glycol-Water Mixtures

Abstract: Thermal conductivity, density, and viscosity of ethylene glycol – water mixtures have been measured. The measurements have been performed in the temperature range from -−20°C to 180°C for thermal conductivity, from -−10°C to 150°C for density, and from – 10°C to 100°C for viscosity. Prandtl-Numbers calculated with the own experimental data and literature values of specific heat capacity are presented in dependence of temperature and concentration.

Titanium diffusion into LiNbO3 as a function of stoichiometry

Abstract: The diffusivity of Ti into LiNbO3 has been measured as a function of crystal orientation and Li/Nb ratio in the temperature range 980–1112 °C. The Li/Nb ratios of single crystal samples were adjusted by vapor phase equilibration with fixed Li2O activities. No anisotropy of diffusivity with crystal orientation could be detected. The diffusion constants for Ti in LiNbO3 decrease with increasing Li2O content. At 1050 °C, the values decrease from 2.60×10−12 cm2/s at the Li2O‐deficient phase boundary (48.1 mol % Li2O) to 1.06×10−12 cm2/s at the congruently melting composition at (48.6 mol % Li2O) to 0.4×10−12 cm2/s at the Li2O‐rich phase boundary (50.0 mol % Li2O). It is suggested that enhanced lateral diffusion observed for stripe geometry Ti sources results from increased diffusivity in a surface layer formed by Li2O outdiffusion.

Nucleation, crystal growth and the thermal regime of cooling magmas

Abstract: Crystallization at the margin of a quiet cooling magma has been studied numerically, taking into account the kinetics of crystallization. The variables are the latent heat value, the growth and nucleation functions, the initial magma temperature, and the thermal contrast between magma and country rock. We have investigated a wide range of values for these parameters corresponding to natural conditions. We show that after a highly transient stage, crystallization tends toward an equilibrium between heat production (latent heat release) and heat loss. Given the small diffusivity of country rocks, latent heat release is the main factor controlling the temperature evolution. In order to minimize the latent heat release, crystallization occurs at a temperature where nucleation is small. This can be close to either the liquidus or the solidus, depending on the initial conditions. The main process controlling crystallization is nucleation and not crystal growth. Nucleation occurs as a series of sharp pulses followed by longer periods of crystal growth. The nucleation pulses give birth to thermal oscillations. These oscillations can be sustained if the interior magma temperature is above the liquidus independently of the heat loss mechanism. We show that the phenomenon occurs on the scale of a few centimeters which corresponds to the inch-scale layering of many ultrabasic complexes. The model allows us to calculate crystal sizes which are in good agreement with geological observations. The crucial parameters which determine crystal size variations near the margins of igneous bodies are the initial thermal conditions as well as the nucleation and growth functions. In the main cooling regime close to the liquidus, significant size variations can be created by small thermal disturbances.

The Variation of the Gas Transfer Coefficient with Molecular Diffusity

Abstract: We argue that the boundary conditions at the air-water interface lead to a variation of the transfer coefficient with the 1/2 power of the molecular diffusivity for slightly soluble gases. For wind-driven bodies of water the transfer coefficient should vary with the −1/2 power of the Schmidt number and with the 1/2 power of that part of the wind stress transmitted by viscosity. The boundary conditions are contrasted with those at a smooth wall where the mass transfer coefficient varies with the –2/3 power of the Schmidt number. Measurements of the transfer coefficient for N2O, CH4, and He at moderate wind stress in an 18 meter wind-wave tunnel support our arguments.

Techniques of flash radiometry

Abstract: We analyze in detail flash radiometry techniques for the remote sensing of spectroscopic and physical properties of thin condensed matter samples. Such techniques rely on the transient infrared radiation from the sample heated by a short‐duration pulsed radiation. Exact analytical solutions for the conventional transmission radiometry technique (in which the excitation source and the infrared detector are on opposite sides of the sample) as well as the new backscattering radiometry technique (in which the excitation source and the detector are on the same side of the sample) are presented with the effect of heat loss neglected. The analysis allows the determination of the thermal diffusivity or thickness, as well as the absorption coefficients at the excitation wavelength and at the detecting wavelength of the sample from the experimental radiometry profile. The effects of excitation pulse duration and finite rise time of the detection system are discussed. Experiments with pulsed radiometry measurements on thin‐film samples are performed to verify some of these theoretical predictions. Radiation loss and lateral heat diffusion loss are shown to be negligible for thin‐film samples.

Temperature distributions produced by scanning Gaussian laser beams.

Abstract: A general solution is presented for the temperature rise produced by the absorption of a scanning Gaussian laser beam in a solid target. In normalized coordinates, the temperature rise is found to depend only on the ratio of the scan speed to the rate of heat diffusion in the solid and the ratio of the beam radius to the absorption depth. For slow scan speeds the solution simplifies to the steady-state approximation in which the power input is balanced by heat conduction into the solid. For fast scan speeds the solution approaches the energy density limit in which the temperature rise is proportional to the integrated beam intensity. For highly absorbing materials the solution simplifies to the surface absorption approximation. The general solution demonstrates the conditions under which each approximation can be used. Similar solutions are found for the related case of pulsed exposure by a stationary beam. The solution is demonstrated experimentally by exposing thermal paper with a CO2 laser.

Scalar diffusion in simulated helical turbulence with molecular diffusivity

Abstract: We extend the simulation techniques of Kraichnan (1970, 1976) to study the effective diffusivity of a scalar field in a turbulent fluid. In our model we have introduced an adjustable helicity parameter and a technique for simulating molecular diffusivity. The results show that for non-helical turbulence the self-consistent perturbation theory of Phythian & Curtis (1978) gives excellent values for the effective diffusivity over a wide range of values for both the molecular diffusivity and the parameters describing the turbulence.This ceases to be the case immediately the helicity is given a non-zero value. Wide departures are observed between the theoretical calculation and the simulation. Our conclusion is that non-perturbative effects are very important in the presence of helicity.

Photoacoustic measurement of thermal properties of a thin polyester film

Abstract: The phase and the amplitude of the photoacoustic signal are measured as a function of chopping frequency for a thin polyester film, using two different backing materials (water and ethanol). Analysis of the results shows agreement with Rosencwaig–Gersho theory [J. Appl. Phys. 47, 64 (1976)] and provides values of the thermal diffusivity and the thermal effusivity of the sample.

Diffusivity of 3He atoms in perfect tungsten crystals

Abstract: The diffusivity of 3He atoms in perfect crystals of tungsten has been studied employing the atom‐probe field‐ion microscope (FIM) technique. Tungsten FIM specimens were implanted in situ with 300‐eV 3He+ ions, to a fluence of 3×1015 ions cm−2, at specimen temperatures which ranged from 60 to 110 K. The 3He+ ion beam was analyzed magnetically and the ion source was connected to the atom probe through a differentially pumped aperture. At an implantation energy of 300 eV no radiation damage was produced by the implanted 3He atoms. Thus, the state of a tungsten specimen after an implantation consisted of 3He atoms with an initial depth distribution that was determined solely by the range profile of the low‐energy ions. Isothermal annealing experiments between 90 and 110 K were employed to study the kinetics of recovery of the implanted 3He atoms; at 60 K the 3He atoms are immobile. This data, in combination with a suitable diffusion model, was used to determine—for the first time—the diffusivity [D3He(T)] and...

Representative Equations for the Thermal Conductivity of Water Substance

Abstract: The paper documents the development of the available information for the thermal conductivity of fluid H2O since the promulgation of the first international formulation for the transport properties of water substance in 1964. As a result of this development, the International Association for the Properties of Steam has adopted new recommended interpolating equations for the thermal conductivity of fluid H2O at pressures up to 100 MPa and at temperatures up to 800 °C. These new international equations are discussed.

Finite Element Analysis of Nonlinear Water Diffusion During Rice Soaking

Abstract: The formulation of a finite element model is described that could be used to analyze water diffusion during rice soaking with concentration dependent diffusivity and change in the size of rice. The rice is divided into 135 elements and moisture distribution with time is calculated. Knowing the moisture absorbed by each element, the nodal displacements are obtained by minimizing the potential energy of the system. Average mass diffusivity of milled rice decreased from 6.4 × 10−7 to 3.0 × 10−7 m2/hr as the moisture content increased from 13 to 50%. The density and concentration dependent mass diffusivity model adequately described experimental data.

Effects of dilatant hardening on the development of concentrated shear deformation in fissured rock masses

Abstract: This study examines the effects of dilatant hardening on the development of concentrated shear deformation. Specifically, the analysis considers the shear of an inelastic ally deforming rock mass containing a weakened layer of thickness h. The presence of the weakened layer causes localization instability, characterized by an unbounded ratio of a strain increment in the weakened layer to that in the far field, to occur earlier than it would be predicted from the response of the material surrounding the embedded layer. The development of instability in time depends on the ratio of the rate of imposed shear strain to that for fluid mass exchange between the layers, c/h2, where c is an effective diffusivity. In the limit , the pressure in the weakened layer is equal to that in the surrounding material and localization instability occurs at the peak of the drained stress-strain curve. For finite , instability is delayed until the material in the weakened layer has been driven to the peak of its undrained, dilatantly hardened stress-strain curve. The time delay between final instability and the time at which the weakened layer passes the peak of its drained stress-strain curve is called the precursor time tpr because rapid straining of the weakened layer occurs during this period. For small , as appropriate for tectonic applications and most laboratory experiments, a nonlinear asymptotic analysis predicts that , where λ is the half width of the peak of the stress-strain curve, Δ is the difference in the peak stresses of the rock mass and the weak layer divided by λ times the elastic shear modulus, and α is a nondimensional measure of the strength of dilatant hardening. For a wide range of numerical values the precursor times are very short: less than a few hours for tectonic strain rates and less than a few tens of seconds for typical laboratory strain rates.

On the production and dissipation of mechanical energy in the ocean

Abstract: The equation for the conservation of total mechanical energy (kinetic, gravitational, and elastic energy) is derived from the conservation of momentum and mass and averaged over the volume of the oceans to equate the production and dissipation of mechanical energy in a statistically steady ocean. The work done by the atmosphere dominates production and is estimated as 0.1 W/m2 from synoptic data which is consistent with most (but not all) of the reported observations of turbulent dissipation. Potential energy production contributes only .0.2% to the total production implying an eddy diffusivity of buoyancy of 10−5 m2/s and a thermal Cox number of 200. The “low” values of diffusivity derived from microstructure observations appear to reflect a relatively small potential energy production.