Eventos Anais de eventos
COBEM 2019
25th International Congress of Mechanical Engineering
A new approach for computing the total absorptivity of non-gray surfaces in radiative heat exchanges with a participating medium
Submission Author:
Roberta Juliana Collet da Fonseca , RS
Co-Authors:
Roberta Juliana Collet da Fonseca, Guilherme Crivelli Fraga, Francis França
Presenter: Roberta Juliana Collet da Fonseca
doi://10.26678/ABCM.COBEM2019.COB2019-0654
Abstract
This paper proposes a new methodology based on a transmissivity-weighted average temperature of the medium to approximate the total hemispherical absorptivity of non-gray surfaces that bounded and exchange radiative heat with a participating gas. In this sense, this is an extension to a recent method to model the radiative transfer between non-gray surfaces and participating media. The new methodology is assessed for a set of one-dimensional test cases involving non-isothermal mixtures of water vapor and carbon dioxide. The gas properties are evaluated using line-by-line (LBL) spectral data, and the radiative transfer equation is solved through the discrete ordinates method. The accuracy of the proposed methodology is compared against other ways to estimate the total absorptivity of the surfaces, using as reference a solution that truly considers the surfaces to be non-gray. Results show that, as the temperature distribution in the medium gets less symmetric, the transmissivity-weighted average is in general more accurate than an older approach for computing the absorptivity, although the former formulation does not perform as well as others for roughly symmetric profiles. However, additional analyses showed that a possible improvement to this formulation can be achieved by taking into account the temperature of the boundaries when computing the absorptivity.
Keywords
thermal radiation, total absorptivity, line-by-line integration, non-gray walls, medium transmissivity
