+ ------------------ = 5,150 deg. absolute.
13.2 lb. X 0.238
The lower temperature, _t_, we may take as that of the feed water, say
at 100 deg. or 560 deg. absolute, for by means of artificial draught and
sufficiently extending the heating surface, the temperature of the
smoke may be reduced to very nearly that of the feed water. Under such
circumstances the proportion of heat which can be realized is
5,150 deg. - 560 deg.
= --------------- = 0.891;
5,150 deg.
that is to say, under the extremely favorable if not impracticable
conditions assumed, there must be a loss of 11 per cent. Next, to give
a numerical value to the potential energy, H, to be derived from a
pound of carbon, calculating from absolute zero, the specific heat of
carbon being 0.25, and absolute temperature of air 520 deg.:
Units.
1 lb. of carbon X 0.25 X 520 = 130
12.2 of air X 0.238 X 520 = 1,485
Heat of combustion = 14,544
------
16,159
Deduct heat equivalent to work of \
displacing atmosphere by products of }
combustion raised from 60 deg. to 100 deg., } 32
or from 149.8 cubic feet to 161.3 }
cubic feet, /
------
Total units of heat available 16,127
Equal to 16.
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