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Show is clearly good agreement between the experimental result and predicted value. Thus, if any existing furnace has been modeled with C F D , thermal properties of invisible structures such as a wall retainer must be included in the C F D model to avoid generation of unexpected impractical results. 3.2 Thermal behaviors of furnace elements To explain the thermal behavior of two types of industrial furnaces, thermal fluxes into furnace elements such as work, atmosphere, the thermal insulation wall and exhaust were estimated in detail. These values were estimated from derivatives of temperature rise in the atmosphere and work and for heat loss by exhaust. For data processing, thermal properties of each element were considered. Figure 12(a)(b) shows heat fluxes into the work installed in the directly heating and indirectly heating furnaces versus atmospheric temperatures. Here we define a heat flux to be positive when the heat moves into the work. In figure 12(a), heat fluxes measured for four fan rotating speeds are presented simultaneously to make clear the effect of rotate of atmosphere circulation on the heat flux profile. It is noted that, these flux values include both the convective heat flux and the radiant heat flux simultaneously. It is evident that these profiles are almost the same and do not depend on the rate. The peak existing around the temperature 650K shows that the heating rate has a maximum value around this temperature, and thus that the temperature difference between the atmosphere and the work has a maximum value. However, such behavior strongly depends on the heating pattern resulting from furnace operating conditions, and thus position of the peak is not important. It should be noted, though, that the heat flux profile very weakly depends on the rate of circulation. This means that the circulating rate very weakly affects the flow pattern in the working space. Figure 12(b) shows the heat flux to the work for the indirectly heating furnace. For temperatures up to 1100/f, there are 2 different slopes in this flux profile. This is caused by a change in the emissivity of the work surface owing to oxidization of surface. The emissivity changes 0.07 to 0.7 at a work tamperature about 1000JT. Figure 13(a) (b) shows the rate of heat input into the atmosphere for both types of furnaces. The horizontal axis indicates the atmospheric temperature, and the vertical axis the heat input rate. For the directly heating furnace, heat input rate profiles were almost the same shape for each fan rotating speed and decreased monotonically. O n the other hand, for the indirectly heating furnace, once the heat input rate increased and peaked around 600A^, it then decreased monotonically. This difference in the shape of profiles between two the types of furnace is immediately related to the difference in method of heating (i.e. direct or indirect heating). In the direct heating furnace, the atmosphere is the flue gas just combusted in the burner. The furnace elements are threfore heated immediately, and the heat input rate is maximum at the beginning of heating. In the |