Heat Transfer In Semitransparent Medium Research Articles

Improved Monte Carlo method for radiative heat transfer in semitransparent media with BRDF surface

This paper proposes an improved Monte Carlo method (IMCM) for the radiative heat transfer solution in semitransparent media with BRDF surface for the first time. This method not only keeps the strong points of high precision and excellent applicability to the calculation of radiative heat transfer in complex shape scattering media with BRDF surface, but also overcomes the shortcomings of time-consuming for huge amounts of energy beams tracing in the Monte Carlo method. In the IMCM we developed, the energy beams of reflection or scattering can be worked out by proportional iteration accumulation. The scattering and reflection process only need to be sampled twice rather than lots of scattering and reflection energy beams tracing. This improvement not only retains the high accuracy of the MCM, but also greatly improves the calculation efficiency. A number of radiative heat transfer problems in semitransparent media enclosure with BRDF surface are studied. The effects of absorption coefficient, wall emissivity and scattering characteristics on radiative heat transfer are analyzed. Results indicate that the IMCM is a very efficient method with high precision for solving radiative heat transfer.

Improved teaching-learning-based optimization for estimation of temperature-dependent radiative properties of semitransparent media

Inverse estimation of temperature-dependent refractive index and absorption coefficient of semitransparent media is studied in this work. The forward transient coupled radiation-conduction heat transfer in semitransparent media is simulated by the finite volume method. The time-varying radiative response signals at the boundary (not the laser irradiation boundary) is adopted as measurement information in the inverse model. An improved teaching-learning-based optimization (ITLBO) algorithm is developed to retrieve the temperature-dependent refractive index and absorption coefficient simultaneously. Effects of model parameters (i.e. the laser heating time and measurement errors) and thermophysical parameters (i.e. the thermal conductivity and heat capacity) on the estimated results are analyzed thoroughly. All the retrieval results show that the inverse model and inverse algorithm is accurate and effective for predicting the temperature-dependent radiative properties of semitransparent media.

Specifics of Heat-Transfer Through the Melting Tank Wall in a Glass Furnace

Amethod was developed for performing engineering calculations of the thermal resistance of the glass layer at the wall that makes it possible, by taking account of the physical crux of the process of heat transfer in semi-transparent media, to secure accuracy and simplify the determination of the temperature regimes in the melting tank of a glass furnace.

Diffusion Approximation to Radiation Heat Transfer in Semitransparent Medium

Conduction-radiation heat transfer problem is usually formulated with a highly nonlinear integrodifferential equation. In this paper we describe a simple technique for modeling radiation heat transfer in a semi-transparent medium with arbitrary varying spectral absorption coefficient and purpose a computational model (described by a coupled system of elliptic-parabolic PDEs) based on flux limited diffusion theory. Numerical simulations of a glass cooling problem in one dimension show that the proposed method is comparable to a higher order discrete ordinate (S8) method.

An Iterative Technique for Coupled Conduction–Radiation Heat Transfer in Semitransparent Media

An iterative technique is developed to solve coupled conduction–radiation heat transfer in semitransparent media. Apart from a high convergence rate, the present algorithm preserves the conservation nature of the governing equation far better than other common methods and it is readily combined with other methods in solving radiative transfer. Using the technique described in this study, parametric studies are carried out for coupled heat transfer in a semitransparent slab and the results illustrate the “peak” effects of wall emissivity and scattering albedo on conductive and radiative heat fluxes, which are rarely mentioned in the existing research.

Natural element method analysis for coupled radiative and conductive heat transfer in semitransparent medium with irregular geometries

This paper analyzes the radiative heat transfer problem coupled with conduction in an absorbing, emitting and isotropically scattering medium with the irregular geometries using the natural element method (NEM). Two kinds of optical boundary conditions are considered: semitransparent boundary with diffuse reflection and transmission of radiation and opaque gray boundary. The boundary is kept at constant temperature or subjected to the convective heating (cooling) and irradiation of black surroundings. The NEM as a meshless method is a relative new numerical scheme in the field of computational mechanics. It has been employed to solve the radiative heat transfer recently. In this paper, we first validate the natural element solutions in dealing with the coupled heat transfer problem with the semitransparent surface considering mixed boundary conditions by comparison with those reported in the literature. Afterward, we study the steady state and transient heat transfer problems coupled with radiation and conduction in the semicircular enclosure with an inner circle. For the steady state coupled heat transfer, only one surface with convective heating and irradiation of black environment is considered semitransparent, while other surfaces are opaque and subjected to constant wall temperature. For transient coupled heat transfer, the conditions of convective heating and environment irradiation are set on two surfaces that are semitransparent and opaque, respectively. Effects of various parameters such as the conduction–radiation parameter, refractive index of the medium, extinction coefficient, scattering albedo, convective heat transfer coefficient and the temperature of the black surrounding are analyzed on the temperature distributions in the medium.

Coupled infrared radiation and phase-change heat transfer in semitransparent medium

The infrared radiation transfer should be considered together with other heat transfer process in the phase change of the semitransparent medium.Solidification heat transfer via absorbing,emitting and isotropically scattering in 2-D rectangular semitransparent medium were analyzed.Solidification was assumed to occur over a range of temperatures,and liquid-,mushy-and solid-zones were considered.The enthalpy-based energy equation was solved by the finite volume method.The infrared radiation transfer was solved by the Monte-Carlo method.The results of 1-D phase change heat conduction and 2-D transient coupled infrared radiation and conduction were in good agreements with published data.Effects of various parameters,such as extinction coefficient,refractive index,conduction-radiation parameter and latent heat,et al.,on temperature and liquid fraction distributions in the medium were studied.Some of these thermal optical property parameters were found to have significant effects on the results.

Coupled radiation and solidification heat transfer inside a graded index medium by finite element method

Effects of thermal radiation on solidification heat transfer must be considered inside semitransparent media. This paper investigates coupled heat transfer of solidification and radiation within a two-dimensional rectangular semitransparent medium having gradient index. Solidification process is supposed to happen at some temperature range, and accordingly three zones including liquid-, solid- and mushy-zones exist in phase-change media. In different phase field, parameters of thermophysical property are assumed different and those of radiative property are assumed same. Governing equation includes conduction, radiation and phase-change terms, and radiation and phase-change are treated as source terms in the equation, respectively. A Galerkin finite element method is used to solve energy equation of coupled radiation and phase-change heat transfer. This paper analyzes effect of thermal radiation on phase-change heat transfer and those of refractive index distributions on temperature fields and liquid fraction distributions during radiation–solidification coupled heat transfer. From the results, we can find that refractive index gradient has a major influence on phase-change process and compared with the case of smaller index gradient, bigger gradient can speed up phase-change heat transfer in semitransparent media.

Radiant-conductive heat transfer in semitransparent medium with phase transition at boundaries with different absorptivity

The one-phase Stefan problem was simulated numerically in a layer of semitransparent medium with different emissivity factors at the right moving boundary. The effect of optic properties of irradiated surface on formation of temperature fields and radiation flux densities was demonstrated.

FPM computations of glass cooling with radiation

This article addresses a new approach for computations of radiative heat transfer in cooling glass. The new solution combines meshfree finite pointset method (FPM) and models of radiative heat transfer in semi-transparent media. This allows to exploit the advantages of particle methods, like their natural capacity to follow changes of deforming geometries, and to reconstruct time evolution of temperature fields due to conduction and radiation effects. Special attention is paid to the radiation as a dominant mechanism of heat transport in high temperatures in semi-transparent materials (e.g. glass). The paper begins with a brief presentation of FPM. It is followed by a discussion of mathematical models of radiation used in computations. The closing part gives a concise review of results of numerical simulations.

Spectral Element Approach for Coupled Radiative and Conductive Heat Transfer in Semitransparent Medium

A spectral element method is presented to solve coupled radiative and conductive heat transfer problems in multidimensional semitransparent medium. The solution of radiative energy source is based on a second order radiative transfer equation. Both the second order radiative transfer equation and the heat diffusion equation are discretized by spectral element approach. Four various test problems are taken as examples to verify the performance of the spectral element method. The h-and the p-convergence characteristics of the spectral element method are studied. The convergence rate of p refinement for different values of Planck number follows the exponential law and is superior to that of h refinement. The spectral element method has good property to tolerate skewed meshes. The predicted dimensionless temperature distributions determined by the spectral element method agree well with the results in references. The presented method is very effective to solve coupled radiative and conductive heat transfer in semitransparent medium with complex configurations and demands little on the quality of mesh.

Least-Squares Spectral Element Method for Radiative Heat Transfer in Semitransparent Media

Least-squares spectral element method based on the discrete-ordinate equation is developed to solve multidimensional radiative heat transfer problems in semitransparent media. An efficient algorithm for implementation of the method is presented. Chebyshev polynomials are employed as basis functions for the spectral element discretization. The p-convergence characteristics of the least-squares spectral element method are studied. The convergence rate is very fast and approximately follows the exponential law. Four test problems are taken as examples to verify the least-squares spectral element formulation. The predicted temperature distributions and radiative heat flux are determined by the least-squares spectral element method and compared with data in the references. The results show that the least-squares spectral element method developed in this article has good accuracy for solving multidimensional radiative heat transfer problems.

Verification of numerical simulation method for entropy generation of radiation heat transfer in semitransparent medium

The numerical simulation method of radiative entropy generation in participating media presented by Caldas and Semiao [Entropy generation through radiative transfer in participating media: analysis and numerical computation. JQSRT 2005;96:423–37] is extended to analyze the radiative entropy generation in the enclosures filled with semitransparent media. A discrete ordinates method is used to solve radiative transfer equation and radiative entropy generation. Two different examples are employed to verify the numerical simulation method of radiative entropy generation in the enclosure. Numerical results of dimensionless radiative entropy generation of enclosure are identical to that of entire thermodynamics analysis for the enclosure system. This numerical simulation method can be used in the entropy generation analysis of high-temperature systems such as boilers and furnaces, in which radiation is the dominant mode of heat transfer.

A quasi diffusive reflective method for the calculation of radiative heat transfer in semitransparent media between parallel planes with angle dependent reflection behaviour

The problem of radiation heat transfer in a semitransparent infinite plane parallel layer with purely diffusive reflection, emission and transmission behaviour (referred to as optical boundary conditions), in which the temperature depends only on the coordinate perpendicular to the boundaries, can be solved exactly by using exponential integrals of different orders. On the other hand the attenuation for the reflected, emitted and transmitted heat currents in the case of specular reflecting, emitting and transmitting boundaries has to be described by more complicate functions or the problem has to be treated by different methods as the discrete ordinates method (DOM). Within this work, a new method to describe radiation heat transfer for this geometry especially in the case of strongly angle dependent optical boundary conditions, including total reflection as described by Fresnel's equations, is developed. This method uses discrete angle ranges with averaged optical properties of the boundaries as well as the exponential integral formalism and is therefore referred to as quasi-diffusive reflective method (QDR-method). Exact solutions and solutions by means of the QDR-method including heat transfer by conduction are compared. The results of the QDR-method are sufficiently accurate in the most practical cases and allow calculations with a temperature dependent absorption coefficient in a much easier way.