Effect Of Thermal Anisotropy Research Articles

Thermal anisotropy in binary alloy solidification: An equivalent isotropic model

A continuum mixture model is proposed for phase change of binary alloy including the effect of thermal anisotropy. Thermal anisotropy is incorporated by an additional departure source in the conventional isotropic heat transfer-based energy equation. The governing equations for heat, mass, momentum, and species transport are solved using implicit finite volume method. The pressure and velocity in the momentum equation are coupled using SIMPLER algorithm. The solute mixture concentration is updated using two commonly used methods, the lever rule model and the Scheil rule model. A comprehensive study is made to investigate the effect of thermal anisotropy on solidification physics and final macrosegregation pattern after complete solidification for two cases: one with three sides of the enclosure insulated where planar front generates and the other with two opposite sides insulated where irregular front evolves. The directional effect of thermal anisotropy ratio (AR) on binary alloy phase change behavior has been investigated in detail.

Combined Effect of Thermal Anisotropy and Forced Convection on the Growth of Binary Alloy Equiaxed Dendrites

A numerical model has been developed to simulate the growth of an equaixed binary alloy dendrite under the combined effect of thermal anisotropy and forced convection. A semi implicit–explicit approach is used where the velocity and pressure fields are solved implicitly using the SIMPLER algorithm, while energy and species conservation equations are treated explicitly. The effect of thermal anisotropy present in the solid crystal is implemented by the addition of a departure source term in the conventional isotropic heat transfer based energy equation. The departure source represents the anisotropic part of the diffusive term in the isotropic heat transfer based energy equation. Simulations were performed to find the relative effect of convection strength and thermal anisotropy on the growth rate and morphology of a dendrite. Subsequently, parametric studies were conducted to investigate the effect of thermal anisotropy ratio, inlet flow velocity, undercooling temperature, and the relative strength of the thermal to mass diffusivity ratio by analyzing the variation of the equilibrium tip velocity of the top and left arms, the arm length ratio (ALR), and the equivalent grain radius. Based on simulations, a chart has been developed, which demarcates different regimes in which convection or thermal anisotropy is the most dominant factor influencing the dendrite growth rate. The model has also been extended to study the growth of multiple dendrites with random distribution and orientation. This can be useful for the simulation of microstructure evolution under the combined effect of convection and thermal anisotropy.

A Numerical Study on Heat Transfer and Lubricant Depletion on an Anisotropic Multilayer Hard Disk

This paper presents a numerical investigation on the effect of thermal anisotropy of the top layer alloy on heat transfer and lubricant depletion on the disk surface in a heat-assisted magnetic recording (HAMR) system. The disk consists of multilayer structures and a thin layer of lubricant on the top surface. Cases under different laser powers and initial lubricant film thicknesses are examined. The top-layer alloy thermal anisotropy does show non-negligible effect on the heat transfer and lubricant depletion. With the top-layer alloy being more anisotropic, higher temperature increase and lager lubricant depletion can be observed on the disk surface. The results also show that the thermal anisotropy effect is more significant under a lower laser power but nearly keeps no much difference under different initial lubricant film thicknesses. Thus it is of importance to include the thermal anisotropy effect of the top-layer Co-alloy when simulating the heat transfer and lubricant depletion in practical multilayer HMAR systems, especially for the cases under the condition of lower laser power, as the effect cannot be neglected under such conditions.

Analytical and numerical investigation of double diffusion in thermally anisotropy multilayer porous medium

Double-diffusive natural convection within a multilayer anisotropic porous medium is studied numerically and analytically. The domain composed of two horizontal porous layers is subjected to a uniform horizontal heat flux and a vertical mass flux, where only the lower one is thermally anisotropic. Darcy model with classical Boussinesq approximation is used in formulating the mathematical model. The effect of thermal anisotropy and the relative width of the two layers on the flow and transfers is illustrated with characterising the transitions from the diffusive to the convective solution. Results were well compared with respect to a developed analytical approach, based on a parallel flow approximation for thermally anisotropic multilayer media.

Representations of currents and magnetic fields in anisotropic magnetohydrostatic plasma: 2. General theory and examples

We develop a general treatment of field‐aligned currents in quasi‐static adiabatic plasma. The formalism is an extension of an an earlier analysis (Heinemann, 1990) to include electric and gravitational fields. The assumption that the particle motions are adiabatic along the magnetic field leads to an expression for the total current density that is a generalization of expressions given by Grad (1964) and Vasyliunas (1970). The current density is a vector function of the gradients of the field line constants characterizing the plasma and the gradients of field line integrals of the partial derivatives of the parallel pressure with respect to the constants. The use of the expression as the current source in Ampere's law leads to an equation governing the equilibrium of the system of plasma and magnetic field. Examples based on bi‐Maxwellian distribution functions suggest that the effects of thermal anisotropy can be about as large as the currents due to isotropic plasma and that the effects of parallel electric fields are of the same order of magnitude.

Three‐Dimensional Effects in Microcrack Nucleation in Brittle Polycrystals

Stress concentration at vertices where grains of a polycrystal meet at a point is contrasted with stress concentration at two‐dimensional junctions where grains join along a line. Effects of thermal anisotropy and elastic anisotropy orientation mismatches from grain to grain are considered. Special geometries with moduli mismatches are also analyzed to shed light on three‐dimensional vs two‐dimensional behavior. Although there are exceptions, it is generally found that the stress concentration at vertices is more singular than that at junctions. Singularities which are stronger than cracklike singularities (i.e., stress αr−s where s > 1/2) are found, and the implication of such “super singularities” for microcrack nucleation is discussed. Conditions for propagation of microcrack flaws at vertices are analyzed and contrasted with those at junctions.

The effect of thermal anisotropy on the propagation of whistler waves in mixed hot-cold electron plasmas

The first-order CGL fluid equations for electrons including the first-order heat fluxes are applied to the propagation of whistler waves. The dispersion relation of whistler waves is derived for two types of equilibrium electron distribution functions with cold and hot components. The effect of electron temperature anisotropy and the existence of cold electrons on the field-aligned propagation of whistler waves is analysed. It is shown that the electron temperature anisotropy intensifies the tendency of whistler waves to follow the lines of force of static magnetic field, that the existence of cold electrons in an anisotropic plasma further intensifies this tendency, and that under certain conditions the waves propagate only along the static magnetic field.