Training Manual on Energy Efficiency - APO Asian Productivity ...

Table 4-1 Radiant heat loss comparison at various temperatures
C1
( º C)
C2
( º C)
K1
(C1 +273)
K2
(C2 +273)
- 37 -
(K1/K2) 4
Relative
Radiant Heat Transfer
700 20 973 293 122 1.0 (baseline value)
900 20 1173 293 255 2.1
1100 20 1373 293 482 3.96
1300 20 1573 293 830 6.83
1500 20 1773 293 1340 11.02
1700 20 1973 293 2056 16.91
(Note: C1 is hot body temperature and C2 is ambient air temperature)
Energy Efficiency in Furnaces
In other words, the radiation losses from an open furnace door at 1500 º C
are 11 times greater than the losses of the same furnace at 700 º C. A good
practice for iron and steel melters is to keep the furnace lid closed at all times
and maintain a continuous feed of cold charge onto the molten bath.
4.7.3 Determining black body radiation at a particular temperature
If a furnace body has an opening, the heat in the furnace escapes to the
outside as radiant heat. Heat loss due to openings can be calculated by
computing black body radiation at furnace temperature, and multiplying these
values by emissivity (usually 0.8 for furnace brick work), and the factor of
radiation through openings. The black body radiation losses can be directly
computed from the curves as given in Figure 4-4.
Figure 4-4 Black body radiation