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456 NOTES ON STEAM.
In a jet condenser the steam and the water are mixed to-
gether, and, therefore, the condensed steam and the water when
leaving the condenser are of equal temperature, and the formula
will change to
h — h
ti = Temperature of mixture.
t\ = Temperature of water when entering condenser.
The other letters have the same meaning as in the previous
formula.
Example.
Steam of three pounds absolute pressure in exhausted into
a jet condenser. The temperature of the cold water entering is
60°. The temperature of the mixture leaving the condenser is
110°. How many pounds of water are needed per pound of
steam condensed ?
Note.—In the steam table, page 451, the total number of
heat units above 32° per pound of steam of three pounds pres-
sure is given as 1124.6 or, for convenience, say 1125.
Solution :
1125 + 32 — 110
W= 110 — 60
W= ^- = 20.1 pounds.
50
Weight of Steam Required to Boil Water.
An approximate rule is to allow that one pound of steam is
condensed for every five pounds of water to be heated to the
boiling point.
It does not make much difference about the pressure of the
steam, as long as it is a few pounds above atmospheric pres-
sure ; for instance, one pound of steam at 10 pounds gage pres-
sure when condensed into water at 212° will give up 973 heat
units, and steam of 100 pounds gage pressure will give up 1003
heat units—a difference of only 30 heat units in steam of 10
pounds gage pressure and steam of 100 pounds gage pressure.
More correctly, the weight of steam required to boil one
pound of water at 212° may be calculated by the formula,
_ 212 — h
X ~~
H— 180
And the weight of steam required to heat one pound of water to
any temperature is obtained by the formula,
- /2 ~ ti
X
H+Z2 — h
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