コイル焼鈍炉における伝熱

抄録

Difference between maximum and minimum temperature in steel coils, when heated for 25h. in an annealing furnace as shown in Fig. 1, is said to be 30-60°C. Theoretical calculation was carried out to know whether this temperature difference is inevitable or not, and reached the conclusion that this range can be reduced to about 5°C, or heating time necessary to get temperature difference within 30°C may be reduced to 15h.
Discrepancy between theory and practice was caused by the following facts:
1). Quantities of heating gas flowing into diffusors (B in Fig. 1) were not equal.
2). Temperature of heating gas flowing into diffusors was high at upper diffusors, and low at lower ones.
3). Outer parts of coils were heated by convection of gas and by radiation from heating zone (F in Fig. 1) whereas the tops and bottoms were heated only by convection. And as temperature of heating zone was higher than that of coil, temperature of the outer parts were apt to be high.
As a heating source of furnace, radiant tubes were often used. Radiant tubes had some defects, i.e., initial cost was expensive, life was short, and thermal efficiency was low. The reason why these were used in spite of such defects, was perhaps due to the fact that distibution of temperature in heating zone was favourable. But, in a good design, uniformity of temperature in coils can be obtained in dependent of temperature distribution in heating zone. It was easy to design a furnace which gave the theoretical temperature distribution.