The Steam Injector
A theoretical and practical treatise on the design and operation of injectors and on the flow of fluids through and the design of nozzles.
Forfatter: V. A. B. Hughes
År: 1912
Forlag: The Technical Publishing Company Limited
Sted: London
Sider: 145
UDK: 621.176
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THE COMBINING NOZZLE.
29
water temperatures. Further, if the proportion of steam to
water is increased or diminished, the cross-sectional area
of the combined jet will be altered, as may also the rate of
condensation of the steam. The velocity of the incoming
steam and also of the water may vary either simultaneously
or independently. The boiler or counter-pressure against
which delivery is being effected may also alter. These
points must affect any decision as to the best form of nozzle
to be employed.
Thus to set the variable quantities out in full, they are : —
(i.) Density of steam.
(li.) Temperature of steam.
(iii.) Temperature of feed water.
(iv.) Ratio of steam to water.
(v.) Velocity of incoming steam.
(vi.) Velocity of incoming feed water.
(vii.) Pressure in vessel being fed.
It is obviously impossible to design any one nozzle to
meet, with the greatest efficiency, all the conditions which
arise even under the most favourable circumstances. The
nozzle must therefore be designed to suit certain conditions
which are a mean between the extremes likely to occur in
service; but this is not easily done. The difficulty in decid-
ing upon the best proportions for the combining nozzle is
evidenced by the variety found in the appliances of high-
class inanufacturers.
Thus, combining nozzles of live steam injectors vary in
length from, about 9 to 24 times the diameter of the delivery
nozzle throat, this measurement being taken between the
exit of the steam nozzle or, if two such nozzles are employed
(see fig. 1 of the forcing steam nozzle and the throat of
the delivery nozzle. The distance between the exits of the
lif ting and the forcing steam nozzles, which also forms a por-
tion of the combining or mixing area of the injector, varies
between four to eight times the diameter of the throat of
the delivery nozzle.
For what is known as “hot-water” injectors, that is,
injectors designeel to deal with high-pressure steam and hot
feed water, the length between the forcing steam nozzle