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Full text of "The Flow Of Gases In Furnaces"

304                                 APPENDIX VIII

Aair = specific weight of air=l kg 29 per cubic meter;
Agaa = weight of gases at combustion-chamber temperature;
in this case 2=1200 and 1.29^-l+a* = 0 kg 239;

K<o = area of orifice in square meters;

KI = coefficient of contraction of the jet, or the ratio
between the area of the contracted vein and
o> (in hydraulics, the contracted vein for a circular
orifice is about 0.67co);

K2=velocity coefficient, or the ratio between the actual
velocity in the contracted vein and the theoretical
velocity (in hydraulics, the velocity in the con-
tracted vein is about 0.970).

KI and /C2 have not been accurately determined for gases.
For the case in hand they may be assumed as equal to unity, and
the formula becomes, for the particular case,

/                                    i   OQ _ 0   93

25. 67=lXlXcoA/19. 62X13. 60X*             = 0m2749.

\             ^

U .
The velocity through the orifice will be
25 . 67 -T- 0 . 749 = 34 m 27 per second.
A combustion chamber of this kind might be constructed in an
old stove, but it would be difficult to maintain with dirty gas.
The furnace dust has a fluxing tendency upon the brickwork and
in many cases forms a heavy deposit. Mr. R. J. Wysor, in his
discussion of Mr. Boynton's paper, presented some interesting
photographs showing the fluxing action experienced in certain
furnaces at South Bethlehem. The fume at these furnaces is high
in alkali.
The stove tested was provided with three chimney valves,
being operated in some runs with all three and in others with
only two. The valves were 20.5 inches in diameter, giving an
area of 0 m2 212 each. The average temperature at the chimney
valve was about 280. The volume of gas flowing per second,
$280=4.75X1+0^ = 9 ni3 63; therefore the velocities would be
9 63
with 3 valves, v = ^    ' 212 = 15 m 10 Per second,
9 63
with 2 valves, v=      '        = 23 m ^ per seconc*-