Eventos Anais de eventos
ENCIT 2022
19th Brazilian Congress of Thermal Sciences and Engineering
ESTIMATION OF THE TOTAL ABSORPTIVITY OF NON-GRAY SURFACES BOUNDING PARTICIPATING MEDIA
Submission Author:
Cesar Augusto Basso , RS , Brazil
Co-Authors:
Cesar Augusto Basso, Roberta Juliana Collet da Fonseca, Guilherme Crivelli Fraga, Francis França
Presenter: Cesar Augusto Basso
doi://10.26678/ABCM.ENCIT2022.CIT22-0363
Abstract
The study of the heat transfer by radiation is complex, but essential for the correct development of systems that operate at high temperatures, such as ovens and furnaces. These systems impose another degree of difficulty for the problem, that is the presence of combustion products, such as carbon dioxide and water vapor, which are opaque to the thermal radiation. These species, which are called participating gases, affect the radiation intensity that permeates them on a spectral level, hence the added complexity to the problem. In order to solve such problems, the line-by-line (LBL) integration of the radiative transfer equation (RTE) has to be performed, in which the intensity field is solved for all portions of the spectrum, providing the most accurate results among the known methodologies. The drawback of this method is its computational cost, since the RTE must be solved for each point of the spectrum and space. Different methods were developed over the years in order to circumvent this difficulty, such as the gray gas (GG), weighted-sum-of-gray-gases (WSGG) and spectral line-based WSGG (SLW) models. These models provide good accuracy of the intensity field of participating media, at a fraction of the computational cost of the LBL solution. The main disadvantage of these models is intrinsic to their formulation, since in these models the spectral information of the participating media is lost. This fact makes it not possible to evaluate a participating medium bound by non-gray walls, which explains the little attention given to studies in this area, most of them focused on black and gray walls. Recent studies proved that assuming a reference temperature for the evaluation of the absorptivity of a non-gray wall bounding combustion products provided a good agreement to the LBL solution. So, the present study provides a deeper investigation of the influence of the required reference temperature for different conditions. A non-gray surface is subjected by thermal radiation travelling through a mixture of water vapor and carbon dioxide, emitted by a black surface in a unidimensional path. Different non-symmetrical temperature profiles are evaluated as well as different concentration of the species and spectral properties for the non-gray surface. Multiple reference temperatures were evaluated and the resulting total absorptivity of the surface is then compared to the LBL solution. From the results obtained, it is possible to estimate a reference temperature that provides accurate results for the total absorptivity of the non-gray surface.
Keywords
thermal radiation, non-gray walls, Heat transfer, total absorptivity
