Abstract
High emissivity coating technology based on the improvement of the wall emissivity is an important heat transfer enhancement technology. However, the experimental results show that the influence of the wall emissivity on the heating process is uncertain. Therefore, the ternary model, which considers the non-gray radiation characteristic of the flue gas, is presented in this paper. Under such model, the analytical expression of the heat flow of the steel slab surface is derived. With the aid of such analytical expression, the influence of the wall emissivity on the heating process is analyzed. The results show that when αgw is smaller than εg, the Qs increases with the increase of εw. In this case, the high emissivity coatings will play a positive role in the furnace heating process. In contrast, when αgw is larger than εg, the Qs decreases when εw increases. At this point, the high emissivity coatings will hinder the furnace heat transfer. When the flue gas is simplified as a gray body, the change of furnace wall emissivity will cause no impact on the heat flow of steel slab surface. This also explains the reason why the Τимoфeeв formula makes no mention of furnace wall emissivity.
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