A COMPUTATIONAL STUDY FOCUSED ON REVEALING THE RELATION BETWEEN CONVECTIVE AND RADIATIVE HEAT TRANSFER FROM A RADIANT HEATED WALL

摘要

Asymmetric thermal radiation is a major reason deteriorating thermal comfort in living environments being caused by wide windows, cold surfaces arising from uninsulated walls or ceilings, and the walls exposed to solar radiation. This leads different parts of a human body to face surfaces having different temperatures, and thus discrete simultaneous radiation gains or losses, which brings discomfort. In the present investigation, to simulate this thermal discomfort condition, realistic thermal boundary conditions, emissivity values, and floor dimensions are selected and applied to an enclosure. The characteristics pertaining to a heated wall, such as the proportion of radiative to convective heat transfer coefficient alongside radiative and total heat flux are examined. To achieve this purpose, a computational fluid dynamics approach for convective data, and a theoretical calculation method for the solution of radiation heat transfer within the chamber are utilized. It is revealed that as the distance between the heated wall and the opposite wall (forming a heat sink that generates an asymmetric thermal radiation) increases from 3 m to 4 m, and to 6 m, the radiative heat transfer coefficient decreases and thus the range of the ratio h(r)/h(c) also narrows from 1.10-1.70 to 1.10-1.55 due to the dwindling effects of radiation. furthermore, three novel correlations comprising the effect of asymmetric radiation in the chamber have been derived for the ratio h(r)/h(c) radiative heat flux q(r), and the total heat flux q(t), the deviation ranges of which remain within +/- 15%, +/- 10%, and +/- 15%, respectively.