of air per 1 lb. of coal; consequently 19 lb. of
gases would be heated by 14,727 units of heat. Hence:
14,727 u.
T = ---------------- = 3,257 deg.
19 lb. x 0.238
above the temperatures of the air, or 3,777 deg. absolute. The temperature
of the smoke, _t_, was 849 deg. absolute; hence the maximum duty would be
3,777 deg. - 849 deg.
--------------- = 0.7752.
3,777 deg.
The specific heat of coal is very nearly that of gases at constant
pressure, and may, without sensible error, be taken as such. The
potential energy of 1 lb. of coal, therefore, with reference to the
oxygen with which it will combine, and calculated from absolute zero,
is:
Units.
19 lb. of coal and air at the temperature
of the air contained 19 lb. x 520 deg. x 0.238 2,350
Heat of combustion 14,727
-------
17,078
Deduct heat expended in displacing atmosphere 151 cubic feet - 422
------
Total potential energy 16,656
Hence work to be expected from the boiler:
/ 3,777 deg. - 849 deg.
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