170
APPENDIX IV
P> ;
only the head, expressed in millimeters of water, corresponding to
the friction loss per second of air at 0° and 760 mm passing through
a brick-lined flue with a velocity of 1 m per second, the sectional area
of the flue corresponding to the equation -~= 1.293.
According to the computations of the author, 0.016 may be
taken as the value of the coefficient m with sufficient precision
for the computations met with in metallurgy. The verification
of this coefficient was made by using it in computations upon
Cowper and Massick and Crook hot-blast stoves.
The formula (A) may be used for all cases in which a current
of gases is flowing through mains or flues.
1. If the current of flowing gas is subdivided into a number of
channels or streams of equal area, the friction loss in each of these
secondary channels is
8 Q
in which
S ,
= ~ and
n
CO
«.=-;
n being the number of secondary channels or flues.
2. If the cross-sectional areas of these secondary channels or
flues are not equal (as, for example, in the gas and air flues of an
open-hearth furnace), the values B=SL and co in the formula
(A), for the parts located between the point where the gaseous
currents separate and the point where the secondary flues join
comprise, respectively, the entire surface touched by the gases in
passing and the sum of the average areas of all the channels or
flues through which the gases pass.
3. If the gas in motion does not fill the furnace to its full
height, the depth of the gaseous stream is computed by the
formula for the inverted weir. The value given to the perimeter
of the channel should be based upon the depth of the stream of
gases. As the. lower stream of the gas in motion slides on top of
the immobile layer of the same gas in the bottom portion of the
flue, it is necessary to take account of the frictional resistance by
considering the entire perimeter of the flowing stream of gases,
including the " free lower surface " of the stream, and the cross-
sectional area of the stream as determined by the depth of the
stream in the flue.