The approximate solutions to the non-linear heat conduction problems in a semi-infinite medium

The approximate solutions to the non-linear heat conduction problems in a semi-infinite medium are investigated. The entire temperature range is divided into a number of small sub-regions where the thermal properties can be approximated to be constant. The resulting problems can be considered as the Stefan’s problem of a multi-phase with no latent heat and the exact solutions called Neumann’s solution are available. In order to obtain the solutions, however, a set of highly non-linear equations in determining the phase boundaries should be solved simultaneously. This work presents a semi-analytic algorithm to determine the phase boundaries without solving the highly non-linear equations. Results show that the solutions for a set of highly non-linear equations depend strongly on the initial guess, bad initial guess leads to the wrong solutions. However, the present algorithm does not require the initial guess and always converges to the correct solutions.     

Solution of non-linear inverse heat conduction problems using the method of lines

 Two space marching methods for solving the one-dimensional nonlinear inverse heat conduction problems are presented. The temperature-dependent thermal properties and the boundary condition on the accessible part of the boundary of the body are known. Additional temperature measurements in time are taken with a sensor located in an arbitrary position within the solid, and the objective is to determine the surface temperature and heat flux on the remaining part of the unspecified boundary. The methods have the advantage that time derivatives are not replaced by finite differences and the good accuracy of the method results from an appropriate approximation of the first time derivative using smoothing polynomials. The extension of the first method presented in this study to higher dimensions inverse heat conduction problems is straightforward. Received on 3 May 1999     

The similar solutions of nonlinear heat conduction equation

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Global existence and exponential stability of solutions to thermoelastic equations of hyperbolic type

In this paper we prove the global existence and exponential stability of solutions to thermoelastic equations of hyperbolic type provided that the initial data are close to the equilibrium and the relaxation kernel is strongly positive definite and decays exponentially. Moreover, the global solution, together with its the third-order full energy, is exponentially stable for any t > 0.     

A phase-field study on the oxidation behavior of Ni considering heat conduction

Phase-field modeling approach has been used to study the oxidation behavior of pure Ni when considering heat conduction. In this calculation, the dependence of the coefficient of the Cahn–Hilliard equation Lc on the temperature T was considered. To this end, high-temperature oxidation experiments and phase-field modeling for pure Ni were performed in air under atmospheric pressure at 600,700, and 800?C. The oxidation rate was measured by thermogravimetry and Lc at these temperatures was determined via interactive algorithm. With the Lc-T relationship constructed, oxidation behavior of Ni when considering heat conduction was investigated. The influence of temperature boundaries on the oxidation degree, oxide film thickness, and specific weight gain were discussed. The phase-field modeling approach proposed in this study will give some highlights of the oxidation resistance analysis and cooling measures design of thermal protection materials.     

On the stability of solutions of a non-linear, non-autonomous equation

Sufficient conditions for the stability of solutions of the equation

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are deduced. These conditions depend on coefficient ratios a/c and b/c as well as on initial conditions. As an example the pendulum of variable length is discussed.     

Two exact solutions of the DPL non-Fourier heat conduction equation with special conditions

This paper presents two exact explicit solutions for the three dimensional dual-phase lag （DLP） heat conduction equation, during the derivation of which the method of trial and error and the authors＇ previous experiences are utilized. To the authors＇ knowledge, most solutions of 2D or 3D DPL models available in the literature are obtained by numerical methods, and there are few exact solutions up to now. The exact solutions in this paper can be used as benchmarks to validate numerical solutions and to develop numerical schemes, grid generation methods and so forth. In addition, they are of theoretical significance since they correspond to physically possible situations. The main goal of this paper is to obtain some possible exact explicit solutions of the dual-phase lag heat conduction equation as the benchmark solutions for computational heat transfer, rather than specific solutions for some given initial and boundary conditions. Therefore, the initial and boundary conditions are indeterminate before derivation and can be deduced from the solutions afterwards. Actually, all solutions given in this paper can be easily proven by substituting them into the governing equation.     

On the thermal rectification factor in steady heat conduction

Thermal rectification in heat conduction problems has been extensively studied in planar slabs. Here we consider the rectification problem in planar, cylindrical and spherical geometries involving two layers one of which has a temperature variable heat conductivity. The rectification factor is analytically calculated. It is shown that a maximum theoretical value of 1.618 is obtained.     

Bounds for the effective heat conduction coefficient

The linear problem of the steady-state heat conduction is studied in isotropic nonhomogeneous hollow rigid bodies. Upper and lower bounds are derived for the effective heat conduction coefficient. It is proven that, the effective heat conduction coefficient of a compound body is between the weighted arithmetic and harmonic means of heat conduction coefficients of the homogeneous body components.     

On the heat conduction problem and a design principle for plasma arc furnace

In this paper a plane heat conduction problem with variable coefficients of heat conductivity K(T) is analysed with given electric power supplied to the plasma arc. The governing equation for unknown temperature distribution is a nonlinear one with a function as its nonhomogeneous term. To make the problem attractable by the method of separation of variables, a set of transformation of governing equation is introduced. An explicit simple formula is found for the efficiency of the furnace , depends linearly on r_o, the nondimensional distance between the arc and surface of melted material, as well as on another nondimensional quantity Q, we describe the above in detail in this paper. This relationship holds for r_o<0.4 and gives a good guidance for the design of furnace.Institute of Mechanics, Academia Sinica     

On the similarity solutions of wave propagation for a general class of non-linear dissipative materials

Deductive similarity analysis is employed to study one-dimensional wave propagation in rate dependent materials whose constitutive laws are special cases of Maxwellian materials (σ_t = φ(ε, σ)ε_t + ψ(ε, σ), ε = strain, σ = stress). The general problem is shown not to have a similar solution although many special cases have the independent similar variable (x ? c)/(t ? d)^e. These cases are studied and tabulated. Analytic similar solutions are presented for several cases and a discussion of permissable boundary conditions is given.     

Dynamical behavior of a mechanical system including Saint-Venant component coupled to a non-linear energy sink

Multi-scale vibratory energy exchange between a main oscillator including Saint-Venant term and a cubic non-linear energy sink is studied. Analytically obtained invariant manifold of the system at a fast time scale and detected fixed points and/or fold singularities at a first slow time scale let us predict and explain different regimes that the system may face during the energy exchange process. The paper will be accompanied by some numerical results confirming our analytical predictions.     

Some self-similar solutions of two-temperature hydrodynamic equations with allowance for nonlinear heat conduction and exothermic reactions

Processes occurring in plasma produced as a result of the interaction of powerful radiation fluxes with matter can be divided into three stages: absorption of radiation on the matter boundary, subsequent heating and compression of the central part of the target for the purpose of creating the conditions necessary for the initiation of an exothermic reaction and, finally, propagation of an exothermic reaction wave through the ambient matter. The present paper is devoted to an investigation of the last stage, a reaction wave igniting initially cold matter. The main method for the theoretical investigation of the processes described is a numerical solution of the equations of motion of a two-temperature gas with allowance for the physical processes occurring in a completely ionized medium: electron heat conduction, radiative losses, energy transfer between electrons and ions, and others. In view of the complicated nonlinear nature of the system of partial differential equations describing the process, searches for possible self-similar solutions are of interest. These solutions can be used as tests in calculating a complete system of equations; by means of them it is also possible to investigate asymptotic laws of exothermic reaction wave propagation.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 145–151, March–April, 1986.