Thermal impedance estimations by semi-derivatives and semi-integrals: 1-D semi-infinite cases

Simple 1-D semi-infinite heat conduction problems enable to demonstrate the potential of the fractional calculus in determination of transient thermal impedances under various boundary conditions imposed at the interface (x=0). The approach is purely analytic and very effective because it uses only simple semi-derivatives (half-time) and semi-integrals and avoids development of entire domain solutions. 0x

Study of a double-layered sphere melting subjected to conditions of not uniform heat flux

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.This paper deals with solid/liquid transition in a double-layered micrometric composite spherical particle metal/ceramic injected into a high temperature plasma jet of argon-hydrogen. The analysis focuses on tracking the particle following its trajectory in order to consider its thermal heat history. The heat transfer equation is formulated by using the enthalpy method and its discretization is carried out by a technique of second order finite volumes in time and space. The obtained results show the significant effect of the geometrical parameters, the phase change and the coupled heat transfer.cs201

Numerical simulation of convective flows occuring during AL-4.1WT%CU solidification

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.This study presents a numerical simulation of the convective laminar flow, driven by combined thermo-solutally buoyancy forces, under a uniform horizontally applied magnetic field, held during the solidification of a molten alloy Al- 4.1wt%Cu filled in a rectangular cavity. The continuum model, of Bennon and Incropera [1], was used in the development of the mathematical model, representing the solidification phenomena. Following this model, the alloy solidification process is governed by continuity, Navier-Stokes, energy, species and electrical potential conservation equations. Here solved by using finite volume method. The effect intensity of the magnetic field on convective flow has been investigated. The governing equations are firstly non-dimensionalized and are approximated by using a finite volume method.cs201

Hydromagnetic soret convection in a shallow porous enclosure with a shear stress applied on the free upper surface

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.The fluid flow induced by combined effects of thermal gradient, thermal diffusion, magnetic field and an external shear stress in a horizontal porous layer, subject to uniform heat flux along its long horizontal walls is studied analytically and numerically. The shear stress is applied on the top horizontal free surface while the bottom one is assumed to be rigid. The problem formulation is based on the Brinkman model with the Boussinesq approximation. The governing parameters are the thermal Rayleigh number, RT , the Lewis number, Le, the separation parameter, ϕ, the Darcy number, Da, the Hartmann number Ha, the dimensionless shear stress, τ and the aspect ratio of the enclosure, Ar. The analytical solution is derived on the basis of the parallel flow approximation and validated numerically using a finite difference method. The critical Rayleigh numbers for the onset of stationary, subcritical and oscillatory convection are determined explicitly as functions of the governing parameters for infinite layers in the absence of the external shear stress. The effect of the main governing parameters on the fluid flow and heat and mass transfer characteristics is discussed.cs201

Analytical Computation of Transient Heat Transfer and Macro-Constriction Resistance Applied to Thermal Spraying Processes

International audienceAn analytical solution of the thermal macro-constriction resistance is derived by using the Hankel finite transform and the Duhamel theorem leading to a simple expression of the solution as a serial expansion with fast convergence. The application concerns the thermal macro-constriction resistance estimate during the spreading and coated formation involved in thermal spraying process.ăIn such a process, the heat flux reaches a few hundreds of W / mm 2 while the spreading duration is extremely short (about μs). The phenomena of thermal macro-constriction deposit/substrate interface play are of primary importance because they control the coating cooling and the thermo-mechanical behavior of the deposited layer, as well.ăThe effect of the spreading velocity on the thermal macro-constriction resistance has been studied. Results show the existence of a critical threshold of spreading velocity for which the transient problem has to be considered. On the other side (below the threshold) the study state regime should be sufficient for the macro-constriction estimate

A lattice Boltzmann based investigation of powder in-flight characteristics during APS process, part II: Effects of parameter dispersions at powder injection

International audienceLattice Boltzmann-based (LB) numerical models for axisymmetric plasma jet are developed to investigate particle plasma spraying process. We study the plasma jet and we focus mainly on the plasma-particle exchanges during the powder journey in argon. The effects of injection conditions on the spraying jet and the arrival particle conditions (velocity, temperature, melting rate, ...) are carried out for four selected operating parameters, say particle diameter, injection velocity, injection position (along injector section) and the injection angle at the injector exit. It has been observed that the LB method is a powerful tool for investigating plasma jet flows. It has been also concluded through the tracking model of the micro-sized particles that the present LB-based results agree well with the FD-based results and that the spray stream depends strongly on the studied injection conditions. Besides, it has been found that the splashing phenomenon is found to be a rule governing particle/droplet impact behavior