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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i68 All About Engines
fall of pressure in the moving blades, reaction tur-
bines are often referred to as pressure turbines.
In the Parsons turbine the moving blades are
fixed in grooves round a drum, and between each
ring of these blades there is a fixed ring of blades
attached to the turbine casing. The space between
any two consecutive blades forms a nozzle, and the
blades are so designed as to give these nozzles the
desired shape.
As the steam passes from end to end of the turbine
the pressure falls to that of the condenser, and there
is none left to convert into velocity. It will be almost
at rest relatively to the turbine casing ; and as for
every pressure there is a corresponding temperature
it is clear that the turbine does work by abstracting
heat from the steam with which it is supplied.
The turbine is a heat engine just as Watt probably
understood the ordinary reciprocating engine to be,
and in its broad outline it is subject to the same laws.
But instead of steam expanding in a cylinder behind
a piston having only a straight line motion back-
wards and forwards, necessitating cross head, con-
necting rod, and crank, we have steam expanding
between innumerable thin blades and applying an
even, continuous turning motion to the shaft. More-
over, there are no eccentrics, no sliding valves, no
masses of metal to be alternately heated and cooled,
and no narrow passages through which the steam has
to escape after expansion.
Since in the impulse turbine it is the velocity of
the steam which is being used to produce motion,