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310                                  APPENDIX VIII
The total area occupied by the
passes                                        =0.0110X    704=      7m2    75
The total area occupied by brick    =0.0214X    704=    15m2   07
Checker area                                  = 7.75    +15.07 =    22 m2   82
The perimeter of one pass             =0.105 X       4=      Om    42
The total perimeter                       =0.420 X    704=   295m     68
The heating surface                       =295.68X    25  = 7392m2   00
Heating surface per cubic meter of
free air per second                      =7392    --16.78=    44m2   05
Heating surface per cubic meter at
pressure and average tempera-
ture                                           - 7392    -^ 23.33 =    31m2   68
The average heat transfer rate will be 4586-^7392 = 0.6204
calories per square meter per second for the existing differential.
The average velocity of flow of the air through the checker will
be 23.33-^7.75 = 3 m 01 per second.
The frictional resistance in the checkers by Mojarow's formula
will be 42 mm 80 of water, while there will be a hydrostatic pressure
upward of 9 mm of water, so that the drop through the checker
will be 33 mm 80 of water.
The possibility of increase in blast temperatures is limited
by the possible temperature which may be realized from the
combustion of blast-furnace gas. Mallard and Le Chatelier, in
the course of their work for the Commission de Grisou, determined
the heat capacity of various gases. Working with these data,
it is possible to approximate the instantaneous calorific intensity
of combustion of various fuels under athermal chamber conditions,
as well as the effect of preheating the air or the gas, or both.
Such a curve has been computed for a blast-furnace gas having a
volumetric composition of H2 = 3.92, CO = 23.95, 02 = 0.39,
C02 = 12.96, H20 = 1.65 and N2 = 57.13. This gas has a thermal
value of 1861 calories per 100 molecular volumes (2 m3 232)
equivalent to 835 calories per cubic meter and 93 B.t.u. per cubic
foot. This curve (Pig. 181) shows intersection points which may
be read to approximate the temperature which may be realized
from the combustion of this gas with various air supplies and
preheating conditions.
Table No. 5 gives computations, which are believed to be
self-explanatory, for the plotting of the curve. In making them,
however, it has been assumed that the air is composed of 1 volume