All About Engines
Forfatter: Edward Cressy
År: 1918
Forlag: Cassell and Company, LTD
Sted: London, New York, Toronto and Melbourne
Sider: 352
UDK: 621 1
With a coloured Frontispiece, and 182 halftone Illustrations and Diagrams.
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CHAPTER XII
Power and Its Measurement
WE read in Chapter III. that James Watt’s success
was due largely to his discovery that the steam
engine was a heat engine, and that the steam was
used merely to convey the heat from the boiler to
the engine. It will be clear that before we can hope
to understand the methods that are used to increase
the efficiency of an engine—that is, to increase the
amount of work done per pound of fuel—we must know
how work is measured, how heat is measured, and how
many units of heat correspond to a unit of work.
Though this may sound rather terrifying, it is
not so in reality. When a man goes into a shop and
puts down five pennies for a pound of sugar he knows
what he is going to get for his money. If the
engineer puts a pound of fuel into the furnace he
wants to know what work the engine will do for it,
and he is no more willing to accept short weight in
work than the other man is willing to accept short
weight in sugar.
Now, as we have previously explained, it a weight
of i lb. is lifted through a height of i foot, i ft.-lb.
of work is done. If a weight of 2 lb. is lifted through
a height of 1 foot, or a weight of 1 lb. through a
height of 2 feet, then 2 ft.-lb. of work is done. Simi-
larly, 10 lb. lifted through 25 feet will involve 10 x
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