256
APPENDIX VII
65 m2 00 (700 sq ft). The width might be reduced slightly by
increasing the length. There are advantages in reducing the span
of the roof, as well as disadvantages in making the furnace too
long, but it is possible that a length of 14 m 00 (45.90 ft) with a
width of 4 m 650 (15.25 ft), giving an area of 65 m2 11 (701 sq ft),
would be satisfactory.
The temperature in the heating chamber will be 1800° C.
(3272° F.) for the gases, the roof being 50° to 100° C. (90° to
180° F.) cooler, and the bath from 150° to 250° C. (270° to 450° F.)
cooler. The height of the chamber may be approximated by
Yesmann's formula
in which ht=the thickness of .the layer of gas in motion in meters
(or feet) ;
Qi=the volume of gas in cubic meters (or cubic feet) at
t° temperature;
jB = the width of the furnace in meters (or feet);
A = & coefficient which varies for each value of h
and Bj
t = temperature Centigrade
TABLE 12
TABLE GIVING THE VALUES OF A FOR METRIC UNITS
Values of B
ht
1 mOO
2 mOO
5m 00
Om 30
3.42
3.54
3.62
Om 50
3.29
3.46
3.57
Om75
3.13
3.37
3.54
1 m 00
2.97
3.28
3.53
This formula may be translated to English units as follows: