J. F. Sacadura

Numerical predictions of two-dimensional conduction, convection, and radiation heat transfer. II. Validation

Abstract The research presented in this paper involves the detailed formulation of a Control-Volume Finite Element Method (CVFEM) for the solution of combined-mode heat transfer in participating media. The proposed numerical method accounts for emitting, absorbing, and scattering media in regularly- and irregularly-shaped geometries. In the proposed CVFEM, the calculation domain is divided into three-node triangular finite elements: the geometrical flexibility associated with finite element methods is preserved. Each element is further subdivided in such a way that upon assembly of all elements, complete control volumes are formed around each node in the calculation domain. To account for the directional nature of radiation heat transfer, a spherical envelope, surrounding each node in the calculation domain, is discretized in adjacent non-overlapping solid angles (or control angles). Element-based interpolation functions for the dependent variables, and the subdomain-type method of weighted residuals are used to derive algebraic approximations to the governing equations. Interpolation schemes that guarantee positive contributions to the coefficients in the algebraic discretization equations are used to approximate the convective and radiative fluxes across control-volume surfaces.

Experimental characterization of thermal radiation properties of dispersed media

Abstract As dispersed materials generally are semi-transparent media which absorb, emit and scatter thermal radiation, the predictive modeling of thermal processes involving such kind of materials requires the knowledge of a number of radiative properties to feed the models. These properties cannot be directly measured but are identified from a set of experimental data of radiative flux collected from a sample submitted to appropriate experimental conditions. This paper focuses on identification methodology for thermal radiation properties of dispersed media such as fibers, foams, pigmented coatings, ceramics. After a brief introductive overview of the subject, the parameter identification methodology and two experimental facilities used for radiative properties determination are firstly described. As the identification process involves a solution model for the Radiative Transfer Equation inside the sample, some attention is then paid to the development of RTE solution models well matched to this specific purpose. Two examples of application are described before concluding on the advantages, limitations and remaining difficulties connected to this new and promising metrology of thermal radiative properties of dispersed media.

Thermal Radiative Properties of Complex Media: Theoretical Prediction Versus Experimental Identification

In many engineering applications and natural phenomena, thermal radiation interacts with complex media composed of dispersed phases that may be of different type: solid/solid, solid/gas, or liquid/gas. Most of them are semitransparent media that emit, absorb, and scatter thermal radiation. Heat transfer by combined radiation with conduction or convection in such media is a problem of high practical importance, mostly in situations where radiation is a dominant mode. Improvement of thermal performance of such materials or of the manufacturing processes that involve these media requires the availability of efficient methods (i) for radiative transfer modeling, and (ii) to predict and to experimentally determine the thermophysical properties intended to feed the models. This paper is focused on radiative properties assessment. After a brief overview of the materials and properties of interest, the emphasis is put on methodology of property investigation combining both theoretical prediction and experimental identification. Examples related to different particulate media are presented, showing recent advances and needs for further investigation.

A Novel First-order Scheme For NumericalTwo-dimensional Radiative Transfer Analysis

This paper presents a skewed upwinding procedure for application to the Control Volume Finite Element Method (CVFEM) in the context of radiation heat transfer problems involving participating media. The proposed first order scheme is stable, economical, accurate and it inherently precludes the possibility of computing negative coefficients in the discretized algebraic equations while accounting for the direction of radiant propagation. The suggested first-order skew positive coefficients upwind scheme (SPCUS) is validated by application to several basic two-dimensional test problems, acknowledged by the radiative heat transfer community: its performance has proven to be excellent.