Improvements in Elastic Fluid Turbines.
Year: 1896

page_text: Date of Application, 1st Sept., 1898-Accepted, 14th Nov., 1896
COMPLETE SPECIFICATION.
Improvements in Elastic Fluid Turbines.
I, CLAUDE KENNEDY MILLS, of 23 Southampton Buildings, in the County of
London, Patent Agent do hereby declare the nature of this invention, a com-
munication to me, from Charles Gordon Curtis, Engineer, of 441 Park Avenue,
New York City, in the County of New York and State of New York in the
United States of America, and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement :-
The object of the present invention is to convert the energy of steam or other
elastic fluid under pressure into mechanical power by utilizing its vis vira or
velocity in a turbine in such a manner as to secure not only a higher efficiency,
but also a much lower spoed of revolution than has been obtained from any turbine
heretofore, as well as increased simplicity of the apparatus.
In carrying the invention into effect the turbine is constructed so as to first
secure the highest velocity attainable in the fluid consistent with obtaining the
most economical result. This is done by passing the elastic fluid through an
expansion nozzle which converts all the pressure into vis vina except what may be
required to cause the flow of the fluid in the most efficient manner through the
vane passages and this vis viva is abstracted fractionally and converted into
mechanical rotation by directing the fluid two or more times in succession
against the moving vanes of the turbine, which vanes have only a fraction of the
initial speed of the fluid.
In this way, and if the conditions which will be hereinafter described are
provided, the vis viva is substantially all utilized and a moderate speed of the
turbine is obtained. The turbine is also one of marked simplicity compared with
compound turbines heretofore employed in practical work.
It has been heretofore attempted to convert the entire pressure of the steam
into velocity by means of an expansion nozzle, and to utilize the high velocity
thus obtained upon one set of rotating vanes. This attempt has only mot with
partial success for various reasons. Unless the boiler pressure is exceedingly low,
the cis viva of the steam when fully developed involves so high a velocity that, in
order to utilize it most efficiently, the speed of a single set of vanes would have to
Consequently lower
be so great as to disrupt apparatus
speed than that giving the highest efficiency has been employed, and a reducing
gear has even then been necessary to bring the speed down to the point where it
becomes commercially available.
With the compound turbine herein described however, the speed of the vanes
need not approach the maximum velocity of the fluid jet in order to secure high
efficiency, because the velocity which remains in the fluid jet after leaving toe
first set of vanes is utilized in one or more succeeding sets of vanes. The energy
extracted from the fluid and converted into. mechanical rotation by each set of
vanes is the difference between the vis vira admitted to aud the vis viva flowing out
of the vane passages, and, other things being equal, may be roughly expressed
with reference to each set of vanes, as the difference between the squares of the
velocities at entrance and at issue. For this reason the energy extracted by a set
of vanes is increased without increasing the speed of their rotation by increasing
the velocity of the fluid at the point of admission to the vane passage. It will,
therefore, be seen that by obtaining the maximum available velocity of the fluid
jet before delivering it to the first set of vanes, a greater percentage of the total
energy will be abstracted in the first set of vanes, and the number of subsequent

page_text: sets of vanes required to abstract the remaining energy will be lessened, thus
greatly simplifying the apparatus.
In order to secure the most efficient results, other conditions in the construction
and operation of the turbine should be provided for. These will now be
referred to.
The velocity or vis viva of the fluid jet being abstracted fractionally by the two
or more sets of rotating vanes, it follows that the velocity of the fluid jet will be
reduced by each passage through the rotating vanes. To accommodate the flow
of the fluid jet at the reduced velocities so that its flow will not bo impeded and
no choking will occur, the working passage through the turbine must be enlarged
in the direction of flow directly as the velocity is decreased. It is not necessary,
for this purpose, that the passage through any set of the movable vanes should be
expanded between the receiving and discharging onda of the passage, since the
speed of the jet through a movable passage relative to the walls of the passage is
maintained, though the actnal velocity of the jet is reduced, by the movement of
the passage itself. But in discharging into a stationary passage, a larger cross-
sectional area should be provided, and this cross-sectional area should be main-
tained throughout the length of the stationary passage, so that the fluid jet, in
being presented to the second set of movable vanes, shall occupy a cross section
which is as many times greater than the cross section of the delivery end of the
nozzle as the velocity is times less. It also follows that the second set of movable
vanes must afford this additional cross section.
The retardation of the fluid jet by surface friction, and a similar effect produced
by eddy currents which tend to reconvert the velocity into pressure, are also
important factors in the construction of the turbine. Both of these actions are
referred to hereinafter as "frictional retardation." Unless the former of these
actions is compensated for and the latter is prevented, a considerable loss in
efficiency will occur in the operation of the turbine. To provide against this, a
difference in pressure is maintained between the delivery end of the nozzle and
the exhaust, which pressure is converted into velocity in the working passago of
the turbine by a further expansion of that passage in the direction of flow beyond
that required to take care of the reduced velocity of the fluid jet due to the
mechanical action of the moving vanes. This expansion or enlargement of the
working passage is preferably made throughout the length of the passage in both
its movable and stationary portions, so as to produce a gradual expansion and
hence a constant draft or pull upon the fluid jet in the direction of the exhaust.
The amount of initial pressure in the jet that is necessary to overcone this
frictional retardation is best ascertained empirically, depending as it does upon the
shape and size of the passage and the character of the surface exposed to the
fluid jet. Free flow through the passage without choking and with the highest
attainable velocity at the entrance to each movable part, is the desideratum in
practice. With reference to all conditions, the passages through which the fluid
flows, are enlarged in proportion to the decrease of the fluids velocity whether
caused by the velocity extracting vaues, or by the retardation of flow caused by
frictional consumption of energy, or by the re-developement of heterogeneous
vibration in the fluid. It is preferred to convert into vis rica before the fluid is
delivered to the first set of vanes all the energy contained in the fluid, except the
amount which will compensate for the frictional loss and to counteract the tendency
of the cis rica to be reconverted into pressure.
The expanding nozzle is constructed preferably so as to couvert all the pressure
into velocity, except sufficient pressure to maintain the flow of the fluid jet in the
most efficient manner; but a higher pressure than this may be employed at the
entrance to the working passage of the turbine, in which case the discharging cod
of the delivery nozzle will not be enlarged relatively to so great an extent, and a
portion of the useful or available pressure will be converted into velocity after
the delivery of the fluid jet to the first set of vanes and while it is passing through
the working passage of the apparatus, and the working passage, beyond the
I

page_text: delivery nozzle will be expanded with reference to the conversion of this
additional pressure into vis ia beyond the increased cross section required to
compensate for the decreased velocity produced by the movable vanes, and beyond
that required by frictional retardation.
The working passages of the compound turbines i.e., the passages beyond the
delivery nozzle are constructed preferably with two or more complete circular
ranges of curved vanes, mounted upon one or more drums, wheels or discs, the
succeeding sets of vanes being counoctel by stationary passages which are likewise
curved and change the direction of flow of the jet so as to deliver it to the
succeeding sets of vanes at the saine angle as it is delivered to the first set of vanes
by the delivery nozzle; but a single set of rotating vanes may be employed and
the intermediate stationary passages may serve to deliver the jet successively to
different portious of the vanes of this single set, as will be understood, or the
passages beyond the delivery nozzle may be composed entirely of movable vanes
mounted upon oppositely rotating bodies. The movable vanes are preferably con-
structed on a curve from their receiving ends to a point boyond their centres, from
which point they extend at a lesser angle to their discharging ends, in order to
obtain as much reactive effect as possible. This form of vane also perinits the
fluid jet which is somewhat compressed by the impact against the curved faces of
the vanes to expand to its normal volume in passing along the extended discharging
ends of the vanes and before reaching the points of clearance at the disoburging
ends of the vanes.
The vanes are also preferably given a progressively greater angle at their
receiving ends in successive sets of vanes, to compensate for the decreased velocity
of the jet relative to the speed of the vanes. The intermediate stationary passages
which are employed in the preferred form of the apparatus are wide enough to
receive the jet from all the vanes from which it is discharged, including those into
which the jet may "spill" at the preceding point of delivery, and where the
stationary passages are single or undivided, they are preferably spread out sidewise
at their receiving cuds in the direction of the movement of the vanes to collect the
livided portions of the fluid jet, and these sides converge towards the centre of
the passage so as to reduce the jet to its normal volume. The successivo passages are
likewise set progressively further forward at their forward sides so as to compensate
for the additional "lead" in the dischargo from the movable vanes produced by the
increased ratio of the speed of the vanes to that of the jet. However it is
preferred to make the stationary passages wide enough for all purposes, and to
divide them into a number of parts by means of vanes which have a shape similar
to, the movable vanes. In this way eddy currents, due to a wide passage, are
prevented, the fluid jet occupying only such parts of the divided stationary passage
as it may be delivered to by the preceding set of movable vaues. In the case of
the divided stationary passages, the succeeding passages may be made progressively
of additional width,
It is the design of the turbine herein described to employ at the delivery end
of the nozzle and in the working passage a "jet" of steam or other elastic
fluid, ., a solid stream of the fluid having an oblong form in cross section, whose
thickness bears a considerable proportion to its width, so that its crues sectional
area will be large compared with its perimeter, as distinguished from an anunlar
film of elastic fluid, whose cross-sectional area is small compared with its perimeter.
By this means, the surface friction is greatly reduced, and the efficiency is largely
increased,
In the accompanying drawings forming part hereof,
Fig. 1 is a vertical section taken through the central line of one set of passages
of the preferred form of apparatus;
Fig. 2 is a similar section on a smaller scale of an apparatus of the same kind,
designed to work with a different exhaust pressure;
Fig. 3 is a section on the same scale as Fig. 1, in partial elevation, of an
apparatus working under the same conditions as the apparatus of Fig. 1, but having

page_text: the expansion take place in the working part of the apparatus wholly in the
stationary intermediate passage;
Fig. 4 is a horizontal section through the delivery nozzle, stationary intermediato
passage, and exhaust opening of the apparatus of Figures 1, 2 and 3, the rims
surrounding the two circular ranges of vaues being partly broken away to disclose
the vanes, which are developed in a horizontal plane;
Fig. 5 is a view in diagram illustrating a modified form of the delivery nozzle;
Fig. 6 is a sectional view similar to Fig. 1, and on the same scale, showing a
form of apparatus employing four sets of movable vanes;
Fig. 7 is a sectional view similar to Fig. 4 of the apparatus of Fig. 6;
Fig. 8 is a vertical section of an apparatus having four sets of movable vanes
mounted on soparate wheels, and connected by single or undivided stationary
pussages, the view being on one half the scale of Fig. 6;
Fig. 9 is a sectional view in partial elevation of an apparatus corresponding
to Fig. 8, but proportioned so that a part of the available pressure is converted
into velocity within the working part of the apparatus ;
Fig. 10 is a sectional view taken horizontally through the passages of the
apparatus of Figures 8 and 9; and
Fig. 11 is a vertical section on the same scale aa Fig. 1, showing an apparatus
with oppositely rotating sots of movable vanes, and without stationary intermediate
passages.
Referring particularly to Figures 1 to 4, A is a shaft, mounted in suitable
bearings a, and passing centrally through a fluid tight case B. Within the case 1,
the shaft A carries the wheel or drum C, upon the rim of which are mounted two
sets D. D' of curved vanes, ench set forming a complete circular range of such
vanes extending entirely around the rim of the drum. The vanes of each set are
covered at their outor sides by hoops or rings b. The vanes form horizontal
passages parallel in one plane with the shaft A across the portions of the rim of
the drum which they occupy, these passages being closed at their bottoms by the
rim of the drum, and at their tops by the rings b. E is the stationary intermediate
passage which is carried by the shell B, and occupies the space between the sets
of vanes D. D' in line with, the delivery nozzle and the exhaust opening, this
passage being closed at its bottom by the plate c. F is a pipe extending from
steam boiler or other source of elastic fluid under pressure, and connected at its
end with the expansion nozzle G, which extends through the side of the sbell B
and approaches as closely as practicable the receiving ends of the first set of
movable vanes D, leaving clearance enough, however, for free rotation.
receiving end or throat d. of the expansion nozzle G is smaller than its discharging
ende in order to cause an expansion and convert the pressure of the elastic fluid
into ris sina. H is the exhaust opening leading out of the shell B opposite the
vanes D' from which the fluid jet is discharged. This exhaust opening may be
connected with a condenser or other means for producing less than atmospheric
pressure, or it may open into the air.
The
To comprehend the design of this apparatus and its mode of operation, it is
necessary to analyze what takes place at all points in the passage way through
which the jet of steam flows from the nozzle to the exhaust. The nozzle being set
at the desired angle with reference to the plane of the wheel, the virtual angle at
which the fluid enters the buckets or vanes depends upon the velocity of these
vanes ne compared with the actual velocity of the fluid, and is the resultant of
these two velocities. Since the velocity of the vanes bears a material ratio to that
of the fluid, it follows that the virtual augle of entrance is somewhat greater
than that of the nozzle, and therefore the receiving ends of the vanes should be
set at this inerensed angle in order to avoid impingement of the jet on the rear
faces of the vanes. The fluid having entered the movable passages, sufficient
cross section must be provided to convey it und. discharge it freely on the other
side. If a non-elastic fluid were, being used such as water, no expansion or
enlargement of the movable passages would be needed, because so long as the

page_text: angle of the tails of the vanes or buckets is the same as or at least no less than
the ungle of the nozzle the tails of the passages are necessarily mathematically
capable of discharging the same quantity of fluid that is delivered by the nozzle,
and hence no enlargement of these passages is necessary. With an elastic or
expansion fluid, the same is true merely as regards conducting the fluid. But in
order to permit an expansion of the fluid in the movable passages themselves and
thus maintain a drop in prossure between the ends of such passages, as it is
preferable to do an actual enlargement is provided in these passages. This may
be done either hy diverging the top and bottom walls, or by setting the tails of the
buckets at a greater angle than that of the nozzle, thus providing a virtually
increased cross section of passage at this end; but it is preferred to obtain it in
the former way, and the amount of such expansion will, of course, depend upon
the respective pressures it is desirable to maintain at these points, and the
corresponding volumes.
Owing to the fact that the vanes themselves have a velocity which is considerable
compared with that of the fluid, the latter issues from the vanes at an angle which
is materially greater than that of the tails; this angle being the resultant of the
combined velocities of the fluid and vanes.
In order therefore to receive the fluid as it enters the stationary passage at a
reduced velocity, its receiving end E is set at an angle which is the same as that
nt which the fluid enters it, the opening being just sufficient to include all the
fluid which escapes from the wheel, and the mere fact of setting the passage at
this angle mathematically provides the increased cross section necessary to convey
the fluid at the reduced velocity. From this point to the delivery end of the
stationary passage, the cross section measured at all points at right angles to the
direction of flow should be at least preserved.
In order to provide for friction and maintain the flow, and prevent or diminish
the formation of eddy currents, a gradually increasing cross section is provided
in the stationary passage as well as in the movable passages, this increase in cross
section being adapted to permit the necessary expansion to maintain the desire]
drop in pressure between the terminals of the passage. This increase in cross
section may be secured in several ways; as shown in the drawings, it is obtained
by increasing the depth or radial dimension of the passage, but it may evidently
be obtained by increasing the width or circumferential dimension or both. If the
stationary passage be curved around so as to deliver the fluid to the second set of
vanes at an angle equal to that of the nozzle, as is desirable, a considerable
increase in the radial dimension is necessary to make up for the reduced width of
the passage resulting from the reduced angle of its walls, and to provide for the
additional enlargement necessary to permit the desired expansion.
The illustrations herein given in the drawings are not intended to show the exact
relative proportions of the parts, but merely show the general plan of operation.
In the second set of movable passages, the conditions are similar to those existing
in the first set, the angle of the receiving cuds of the vanes in this case being,
however, somewhat greater owing to the fact that the velocity with which the jet
strikes the vanes is less while the velocity of the vanes remains the saine (if those
two sets of vanes have the same diameter or aro noving at the same rate of
speed) so that the virtual angle of entrance into these passages is somewhat greater
than in the first set. For a like reason, the angle of issue from the second set
into the second stationary passage will be somewhat greater than in the first set,
and hence the receiving end E' of this passage is set at an increased angle. The
receiving ends of the subsequent vano, both movable and stationary, are likewise
set at progressively increasing angles, provision being made in this way for the
reduction in the jet's velocity which takes place in its flow through each set of
movable passages. In each of the subsequent movable and stationary passages,
as in the first, the proper expansion in each portion is provided so as to maintain
the desired pressure difference, the pressure gradually declining through the system
and issuing from the last set of vanes with little or no residual pressure above that
of the exhaust.

page_text: It is preferable that the desired expansion should take place in both the movable
vanes D and the stationary passage E, as illustrated in Figures 1 and 2, so as to
obtain a gradual expansion throughout the system, whether composed of two or
more sets of movable vanes, but the requisite expansion may entirely or largely
take place in the stationary passages E, as illustrated in Fig. 3, in which case the
passages formed by the vanes D have parallel top and bottom sides, the essential
point being that the cross sectional aren of the stationary passage E shall be
sufficiently larger than the cross sectional area at the discharging end of the
npzzle G to accomplish the result stated. The second set of vanes D¹ may
also flare outwardly, or expand, as shown in Figures 1 and 2, or they may have
parallel sides, as shown in Fig. 3. However it is preferred to have the expansion
take place also in the movable passage, so as to provide sufficient expansion to tako
care of the frictional retardation in the movable passage itself.
In Fig. 5 is illustrated a construction in which the side walls of the nozzle are
parallel, but the proper relation is maintained between the receiving and discharging
ends d. e to give the desired conversion of pressure into velocity.
This form, while not so effective, gives approximate results with low ratios of
-expansion.
The, discharging end of the nozzle Gmay be sufficiently larger than the
receiving end d to convert the pressure wholly into velocity, except an amount of
pressure required to supply the frictional consumption of energy in the working
part of the apparatus, and to maintain the flow without developing eddy currents
or what may be termed heterogeneous motion; or the ratio of expansion
between the receiving and discharging ends of the nozzle may be lessoned so as to
deliver the fluid to the first set of vanes at a pressure higher than that thus required.
The former plan is preferable.
It is desirable that the steam should strike the first set of vanes at as high a
velocity as possible, because the greater the velocity at which it strikes the first set
of buckets, the greater the work done in the first set, and hence fewer successive
passages are required to abstract all the energy it contains. By using an expansion
nozzle properly proportioned, the maximum velocity may be obtained that is possible
while still leaving sufficient pressure above that of the exhaust to cause the flow in
the most efficient manner, thus securing the highest aggregate amount of ris viva
at the various points of action and therefore the greatest effect possible from
the fluid.
The difference in presenre that it is desirable to maintain between the terminals
of the working passages of the machine, depends upon the length, size, general
proportions of and the number of bends in the working passages and the character
of the surfaces over which the fluid sweeps, and can only be determined by trial in
cach particular style or size of machine. In large machines, this quantity will be
less than in small machinee, and in machines highly compounded it will be greater
than in those compounded to a less degree. Let it be assumed for illustration the
particular case where the boiler pressure is 150 pounds, and the exhaust 2 pounds per
square inch (corresponding to about 26 inches vacuum), these pressures being absolute
and not by gauge. Let it be assumed that a pressure of, say, 5 pounds above that of the
exhaust is necessary to overcome friction and to cause the flow of the fluid through
the working passage in the most efficient manner, that is, so as to obtain the hig est
aggregate velocities possible at the several points of action-this figure bring used
merely as an illustration. Under these circumstances, the pressure at the delivery
end of the nozzle should therefore he 5 pounds above that of the exhaust,
or 7 pounds (absolute). The true proportions of the nozzle can then be determined
as follows: The small or receiving end is made just large enough to permit the
required quantity of steam to flow to develop the power the turbine is designed for.
This can be ascertained empirically, or it may be calculated approximately by
taking the pressure at this point, which will bo approximately 58 per cent. of tho
boiler pressure (measured above the exhaust), and calculating the velocity developed
at this point due to the drop in pressure. This velocity can be calculated by taking

page_text: the heat units or equivalent work in foot pounds performed by the steam is thus
expanding, and calculating the equivalent velocity of the fluid, assuming that all
the energy in foot pounds becomes converted into an equivalent amount of
vis vira.
Under the conditions assumed, the pressure will be about 90 pounds, and the
velocity between 1300 and 1400 feet per second at the receiving or small end of
the nozzle. Knowing the velocity and the donsity of the flujd, the size or cross
section of the receiving end of the nozzle necessary to conduct a given amount is.
easily determined.
In a similar way the size or cross section of the large or delivery end of the
nozzle can be computed, by first ascertaining the velocity of flow developed by
dropping to the required pressure at this point, and then, knowing the density from
the pressure, furnishing just sufficient cross section at this point to conduct the
same quantity of Buid as passes through the small end, allowance being made in
the case of a saturated vapor, such as steam, for the condensation and consequent.
diminution in volume, which takes place during the given expansion. In the case
assumed as an example, a drop in pressure from 150 pounds to 7 pounds would
develop a velocity of about 3100 feet per second, and the condensation would be
about 15 per cent., so that the volume would be less by 15 per cent. than what it.
would bo were there no condensation.
In the case assumed, the cross section of the larger end of the nozzle should be
about five times as great as that of the smaller end, and this is the general
proportion which it is intended to illustrate in Figures 1 and 3, taken in connection
with Figure 4.
The apparatus illustrated in Figure 2, taken in connection with Fig. 4, is
intended to represent a machine designed to work between a boiler pressure
of 150 pounds and atmospheric pressure; in other words, a non-condensing machine.
In this case, if the loss by friction represents, say, 5 pounds of the whole available
pressure, as before, the pressure at the delivery end of the nozzle will be
about 20 pounds, the speed of the jet will be about 2600 feet per second, and the
discharging end of the nozzle will be about twice as large in cross section as the
receiving end. The excess of pressure at the discharging end of the nozzle over
the atmospheric pressure at the exhaust will be that required to overcome friction
in the working passages of the apparatus and maintain the flow therethrough in the
most effective manner, as before.
It is highly important that the large end of the nozzle be no larger than just
sufficient to conduct the required volume at the pressure and velocity designed to
exist at that point, for otherwise the passage would be too large and there would bo
a less velocity at this point than should exist there, resulting in a loss of power.
It must be borne in mind that the effect obtained from the fluid is as the square of
its velocity at the time it is acting on the vanes, and that therefore a slight change
in velocity causes a very considerable loss of power.
For this reason it is highly important that the correct and highest 'availablé
velocities be obtained at all points where the fluids acts upon the vanes.
It is better to ascertain the exact proportions between the receiving and
discharging ends of the delivery nozzle by careful trial, the rosult being to some
extent influenced by friction in the nozzle itself; the best plan being to vary the
size of the large end of the nozzle, keeping the small end constant, until a pressure
is obtained at this point which is only just sufficient to overcome friction and
tendency to reconversion into pressure in the working passage beyond and at the
same time the cross section is only just sufficient to conduct the quantity of
steam flowing at the particular pressure and velocity existing at this point.
After passing through the first set of vanes or movable passages, the steain or
fluid emerges with a reduced velocity. In the case of two movable passages, let it
be assumed that 40 per cent., of the velocity of the fluid is abstracted at each
passage, leaving only 20 per cent. of the original velocity as it enters the exhausti
corresponding to 4 per cent. of the original energy. Since the energy is proportional

page_text: to the square of the velocity, it is evident that the energy extracted by the first.
movable passage will be 64 per cent. while that extracted by the second movable
passage will be 32 per cent. of the total original energy. On emerging from the
first set of movable vanes and as the steam jet enters the second set of movable
vanes from the stationary passage, its velocity will, therefore, have been reduced
by 40 per cent., and it will now have 60 per cent. of its original velocity. Since the
stationary passage is increased in size inversely as the velocity of the steam jet, it
follows that under the assumed conditions, the stationary passage E will from this
cause be required to be made 100/60 or 1.66 times larger in cross section than the
delivery end of the nozzle G.
At the same time, provision should be made for expanding tho passages to a
further extent as already explained to cause the desired decline in pressure to
overcome surface friction and the tendency to reconvert velocity into pressure by
eddy currents, this decline in pressure being under certain conditions a considerable
portion of the total drop in pressure in the working passage of the turbine. The
entire increase in the cross sectional area at the point fover the pointe is therefore
the product of these two ratios, and this is the proportion intended to be illustrated
in Figures 1, 2 and 3. By observing this relation of the parts, au economical
conversion of the pressure into vis viva and of the vis rica into mechanical pover
will be obtained, while the speed of the movable vanes will be only a fraction of
the speed of the fluid jet.
The proper decline in pressure of the steam in passing through the turbine
depends upon so many conditions that it is best in every case to determine it by
experiment. It will be greater in traversing the first set of vanes than in subsequent
ones, owing to its higher velocity, and likowise it will be greater in traversing the
first set of stationary vanes than in subsequent ones for the same reason.
Allowance should also be made for the fact that the steam in sweeping against
the concave vanes is compressed to a greater or less degree by its own centrifugal
force, so that unless when it leaves each set of vanes it has re-expanded to its
normal voluine, its density at these points will be less than would have been tho
case had there been no centrifugal compression.
This compression may, to a large extent, be reduced by means of the straight or
slightly curved tails (which are shown especially in the cuse of the intermediate
fixed vaues) which allow the steam to flow for a certain length in a straight or
slightly curved course, thus permitting it to expand again and assume more nearly its
normal volume before delivery to the next set of vanes. By these means it is also
possible to re-convert the energy or work expended in contrifugal compression into
velocity or partially into velocity again, thus recovering a large part of this energy
and causing the fluid to impinge upon the second or successive sets of ranes with
additional velocity.
Owing to the various conditions which affect the actual volume at the various
points in the apparatus, the best plan is to ascertain the proper proportion of the
various points in the passages by trial, the essential features of economical working
being that the successive cross sections of the passages should be just large coough
to conduct the fluid without choking it or backing up the pressure at that point,
and so as to obtain the highest velocities practically obtainable at the various
points of action upon the blades, (that is, so as to obtain the greatest sun total of
all the actions upon the successive vanes) and yet no larger than is necessary for
this purpose, otherwise there will be too low a velocity, and a corresponding loss
of energy.
If more than two sets of movable vanes be employed, the principle of operation
and construction is the same, the delivery nozzle having its receiving end of the
precise size required to pass the desired quantity of the fluid and its discharging
end of a size as many times larger as may be required to expand the fluid down
to the pressure required to overcome the frictional retardation in the working
passages of the turbine and give the best result, while the delivery ends of the
succeeding stationary intermediate passages will have their size increased in

page_text: proportion as the velocity of the fluid jet has been reduced and as its volume has
been increased by the decline in pressure. In Figures 6 and 7 is represented a
turbine having four sets of movable vanes D, D', D', D', and three stationary
intermediate passages E, E, E' constructed and operating on this principle. In
this case, and assuming that the apparatus is designed to work between the initial
and terminal pressures before taken for illustration, i.e., a boiler pressure of
150 pounds and an exhaust pressure of 2 pounds per square inch (absolute), the
delivery nozzle G will be proportioned in the manner described so as to expand
the steam down to a given pressure, say 10 pounds at its discharging end, the
remaining pressure above the pressure of the exhaust being that assumed to
maintain the flow in the working passages. If the steam jet enters the exhaust
with 20 per cent. of the original velocity, each of the four sets of movable vanes
will abstract 20 per cent., of the velocity, and will in their order absorb respectively
36, 28, 20 and 12 per cent. of the energy represented by the original velocity, while
4 per cent. of the energy will pass off as residual velocity in the exhaust. The
decline in pressure in the working passages will be such that at the discharge
ends f. f and f of the stationary intermediate passages, the pressures will be less
aud less declining at a certain rate which should be found by experiment in each
particular type and size of machine, and owing both to reduced velocity and to
increased volume of the fluid jet arising from reduced density, the cross sectional
areas at the points f.and will be correspondingly increased over the cross
sectional area of the discharge ende of the nozzle and over each other successively.
The expansion in the working passages is shown in full lines as taking place in
both the movable and stationary passages, whilo by the dotted lines this expansion
is shown as taking place wholly in the stationary passages. The former plan is
preferable.
In Fig. 8 (taken in connection with Fig. 10) is shown an apparatus designed to
have the same proportions of the expanding nozzle and the working passages and
to operate under the same conditions as the apparatus of Figures 6 and 7. It
has the peculiarity in construction of having the different sets of movable vanes
mounted upon separate wheels. It also differs in the construction of the stationary
intermediate passages which will bo presently described.
In Fig. 9 (also taken in connection with Fig. 10) is shown an apparatus in which
the two operations of converting the pressure into vis viva and vis vina into
mechanical power overlap to a greater extent, although the useful or available
pressure is still largely, although not wholly, converted into vis vivu by the
expansion delivery nozzle, which delivers the fluid jet to the first set of movable
vanes at a pressure greater than is required to overcome frictional retardation in
the working passages of the apparatus. In other words the apparatus of Fig. 9
is designed to convert into ris civa in its working passages a part of the pressure
which in the constructions before described is converted into vis viva by the
expansion nozzle. Taking the illustration of initial and terminal pressures of
150 pounds and 2 pounds per square inch (absolute) and assuming, as was done
for the apparatus of Fig. 8, that a pressure of 8 pounds above the exhaust pressure
is required to overcome frictional retardation in the working passages, the
apparatus of Fig. 9 is designed to have a pressure of, say, 20 pounds at the
delivery end e of the nozzle G, and the remaining expansion required to convert
the balance of the useful pressure (10 pounds) into eis viva takes place between the
delivery end e of the nozzle G and the delivery end of the stationary passage E³.
To accomplish this, the delivery end e of the nozzle G and the delivery
ends and of the stationary passages E E' and are given cross sectional
areas increasing in size from one end of the apparatus to the other, the increase at
each point being just sufficient to take care of the increased volume of the fluid
at each point and also to allow for the diminished velocity resulting from its
passage through the previous set of vanes. The expansion for converting the
balance of the useful pressure into vis viva which takes place in the working
passage of the apparatus of Fig. 9, may take place uniformly in both the movable
B

page_text: and stationary passages as illustrated, or it may take place wholly in either the
stationary or movable passages or in a part of the working passages either
movable or stationary or both, but it is preferred to enlarge both the movable and
stationary passages uniformly. At the same time that the expansion of the
working passages to convert the balance of the useful pressure into vis viva is
provided, those passages are expanded to compensate for reduced velocity and
for frictional retardation. The proper proportions will accomplish this combined
result.
The proportions and pressures given are merely for purposes of general
illustration, to show the principles involved in the construction and operation of
the apparatus.
Having thus described the principle of operation and construction of the compound
turbine, reference will now be made to some details of construction which have not
been as yet specifically described. The vanes 9g of each set of movable vanes are
curved from their receiving ends to beyond their centres, and thence to their
discharging ends they are straight or slightly curved, or set at a lesser angle, as
shown in Figures 4, 7 and 10, so as to obtain as much effect as possible from the
fluid before it leaves the vanes. In Fig. 10, single or undivided stationary passages
are shown. These are made wide enough at their receiving ends to receive the
fluid jet from all the movable vanes from which it may be discharged (including
the additional width made necessary by the "spill" of the fluid jet), and the
receiving end of each stationary pasange is given a "lead," that is, set with a
certain advance if necessary over the discharging end of the nozzle or previous
stationary passage to properly receive the discharge from the movable vanes, it
being remembered that owing to the speed of the movable vanes themselves, the jet
issues from them at a point slightly ahead of the point at which it is received. The
amount of this "lead" should inorense at each succeeding set of vanes owing to the
progressively diminishing velocity of the fluid compared with that of the buckets,
as indicated in the drawing. The diverging top and bottom walls of these passages
serve not only to maintain the cross sectional area which would be contracted
towards the discharging ends of the passages if such top and bottom walls were
parallel, but also to give the necessary expansion to maintain the desired drop in
pressure between the ends of the passages.
to
Instead of using single or undivided stationary passages, as shown in Fig. 10, it
is preferred under certain conditions, to use divided stationary passages, as shown in
Figures 4 and 7. These passages are made of sufficient width to receive the entire
discharge from the movable vanes, when running at the normal speed, and may be
made of additional width in succeeding passages to give the necessary "lead
provide for any rate of speed. These passages are divided each into a number of
narrower passages by vanesh which have curved receiving ends and straight
discharging ende, as have the movable vanes, and also have their receiving ends
arranged progressively at a greater angle in the vanes of succeeding passages as
bave the movable vanes in successive sets, in order to receive the jet properly and
furnish the required cross section. As in the case of single fixed passages, the
angles at which their receiving ends are progressively set will determine their
respective cross sections, and by making these angles the same as the angles of issue
from the moving vanes, the requisite cross section will be provided.
Besides the forms of apparatus which have been described, many features of the
invention are involved in the construction and operation of such an apparatus as
that shown in Figure 11, in which only movable vanes are employed in the working
part of the apparatus, the sets of vanes being alternately mounted upon oppositely
rotating discs, and delivering the fluid jet from one ret of movable vanes directly
to another set witbout the interposition of stationary passages. It will be under-
stood that the inovable vanes have all the characteristics of the movable vanes
already described, but that those on one dise are set or curved oppositely to those
on the other disc. In the apparatus illustrated in Fig. 11, the expanding nozzle is
designed to convert all or the larger portiqu of the useful. pressure into.vis pira,
E

page_text: although the overlapping of the operations of couverting pressure into vis viva and
vis viva into mechanical power can likewise be employed in an apparatus of this.
kind.
It will he observed that in all forms of the apparatus the steam or other elastio
fluid is delivered to the working passages practically in the form of a solid stream
or "jet" whose cross sectional area is large compared with its perimeter, and that
this jet acts at one time only on a small section of the vanes of a circular range.
This arrangement has a great practical advantage over one wherein the fluid is.
delivered in the form of an annular film simultaneously to all the vanes of a
complete circular range. In the latter arrangement, in order to reduce the total
cross section of the passage to that required and still have the proper velocity, the
depth of the vanes has to be exceedingly small, and the surface exposed to the
flowing fluid is very large compared with the cross sectional area of the passages..
The result is great loss by surface friction and churning action, and in addition the
clearance space is so extended that it becomes large in proportion to the area of
the passages.
By the expression "frictional retardation" it is meant to include not only the
actual loss of energy by friction in the passages, but also the loss of energy in
available form due to the reconversion of vis viva into pressure or heterogeneous
vibration.
By the expression "expansion nozzle," is meant any nozzle or delivery passage
having an enlarged cross sectional area towards its delivery end considered with
reference to its narrowest part.
By the expression "working passage," is meant that portion of the apparatus.
through which the steam flows, beginning at the delivery end of the expansion
nozzle and ending at the exhaust, whether composed of vane passages, or of vane
passages and fixed passages.
It should be understood that the use of two or more sets of circular ranges of
vanes through which the fluid passes in succession, and of one or more circular
ranges of vanes through which the fluid passes two or more times in succession are
equivalent constructions, and are intended to be included herein.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is:-
1. A compound elastic fluid turbine, wherein the fluid acts upon movable vanes.
two or more times in succession, in combination with an expansion nozzle, whereby
the high velocity developed in the fluid by expansion in the nozzle is fractionally
abstracted by the movable vanes, substantially as set forth.
2. In a compound elastic fluid turbine, the combination with an expansion nozzle.
adapted to convert the pressure of the elastic fluid into velocity while retaining a
pressure in the fluid above that of the exhaust, of a working passago leading two.
or more times successively through movable vanes which abstract the velocity
fractionally, such working passage having increasing cross sectional areas in the
direction of the flow of the fluid sufficient to conduct the required volume of the
fluid at the maximum attainable velocity, so as to obtain the highest velocities
practicable at the two or more points of action of the fluid on the movable vanes,.
substantially as set forth.
3. In a compound elastic fluid turbine, the combination of two or more sets of
rotating vanes and one or more connecting stationary intermediate passages for
delivering the fluid jet to the successive sets of rotating vanes after the first, such.
sintionary intermediate passages being set at their receiving ends at the same angle
as that at which the fluid jet is discharged from the rotating vane passage,.
whereby the cross sectional area provided for the jet in the stationary passage
at its receiving end is substantially the same as the cross sectional area of the
fluid jet as it is discharged from the respective rotating passages, substantially as.
set forth.

page_text: 4: In a compound elastic fluid turbine, the combination of two or more sets of
rotating passages and one or more intermediate stationary passages, each of said
passages having curved side walls having a less angle at the discharging end than
at the receiving end of the passage and with top and bottom walls diverging toward
the discharging end of the passage, whereby the necessary expansion is obtained,
substantially as set forth.
5. In a compound elastic fluid turbine, the combination with a series of sets of
rotating vanes, of a nozzle delivering a fluid jet to a part of the vanes of the first
set, and a series of intermediate stationary passages connecting the vanes and
changing the direction of flow of the fluid jet, said stationary passages being
composed of a sufficient number of vanes to cover the movable vanes through
which the fluid jet passes, and this number of vanes being increased in succeeding
stationary passages to give an increased lead proportional to the diminished velocity
of the fluid, substantially as set forth.
6. In a compound elastic fluid turbine, the combination with a delivery nozzle
arranged obliquely, of two or more sets of rotating vanes having receiving ends
placed at a progressively greater angle in successive sets of vanes, substantially as
set forth.
7. A compound elastic fluid turbine, having in combination the two or more
complete circular ranges of rotating vanes D, D', etc., the one or more inter-
mediate stationary passages E, E, etc., the fluid conduit F, expansion
nozzle G and exhaust H, all constructed, arranged and operating substantially
as described.
Dated Santember 1st 1808
HARRIS & MILLS,
23 Southampton Buildings, London, W.C., Agents.