# Full text of "The Flow Of Gases In Furnaces"

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```DESIGN OF OPEN-HEARTH FURNACES

265

The pass unit will be different for a different wall thickness,
and it may be desirable to try several variations, in order to secure
the most desirable arrangement. An old rule is that the active
heat-storage capacity of brickwork is comprised in the depth of
1.25 in from the surface, giving a wall thickness for maximum
results of 2.5 in (63 mm). When the brickwork is laid up to
secure stability, 9-in straights give very good results. With
thicker walls the time of the cycle must be increased, to develop
the full weight of the brickwork. With the time cycle assumed,
which agrees fairly closely with practical working, a wall thickness
of 2.5 in (63 mm) utilizes its full heat-storage capacity. With a
fifteen-minute cycle a 2-in wall would be desirable, but is probably
a little too thin to give the best operating results.

TABLE 16—Continued

Gas on Gas
*Air on Air
Gas on Waste Gas
Air on Waste
Gas

By using a 2-in (50 mm) brick, the size of the pass and the space occupied will be reduced : 50-7-0.33=?;= ...............
150 mm
6 0 in

Brick thickness ...............
50 mm
2 0 in

Diamet r square pass .........
100 rnm
4.0 in

Wall thickness around pass .....
63 rnm
2 5 in
50 rnrn
2 0 in

Area unit pass = 62 = ...........
0 m2 0361

0 m2 0225

Area of pass opening = ..........
0 m2 0162

0 m2 0100

Area occupied by brick = ........
0 rn2 0199

0 m2 0125

As the unit pass was made the same, the volume of brick and pass in  the   air   checker  will  be changed to Brick = 301. 06X0. 5526= .....
166 m3 37

Pass =301.06X0.4474= .....
134 m3 69

The lineal amount of pass and brickwork is found by dividing
the brick and pass volumes by the area of the brick and pass in
the pass unit. It will generally be found that there is a slight
disagreement between the lengths determined for the pass and the
brickwork. It is preferable to take the highest of the values so
found for determining the size of the space to be occupied by the```