US1475213A - Elastic-fluid turbine - Google Patents

Description

Nov. 27 1923. 1,475,213

H. L. WlRT ELASTIC FLUID TURBINE Filed July 12, 1922 fr; van tor- W MQ'J STATES HARRISON mama wra'r, or scnnnnc'mnr, NEW YORK, ASSIGNOR 'ro GENERAL ELECTRIC COMPANY, A conroaarron or NEW YORK.

ELASTIC-FLUID TURBINE.

Application filed July 12, 1922. Serial No. 574,476.

To all whom it may concern:

Be it known that I, HARRISON LoRING WIRT, a citizen of the United States, residing in Schenectady, in the county of Schenectady, State of ew York, have invented certainnew and useful Improvements in Elastic-Fluid Turbines, of which the following is a specification.

The present invention relates to elastic fluid turbines of the impulse typetand particularly to nozzles for such turbines. ".As' is well understood, the nozzles are stationary, fluid-directing elements which serve to expand the elastic fluid, thereby converting pressure into velocity, and direct it against the adjacent ring of blades. In general the nozzles ,are formed by mounting or arranging guide blades or partitions between two radially spaced concentric rings, the structure as a whole being termed a nozzle diaphragm. The nozzles may extend entirely around the diaphragm providing for complete peripheral admission or they may extend only part way around.

The object of my invention isto provide a nozzle structure which will give an efiiciency higher than has been obtained heretofore, or, in other words, a nozzle structure wherein the losses are reduced, and for a consideration of what I believe to be novel and my invention, attention is directed to the accompanying description and the claims appended thereto.

In the drawing, Fig. 1 is a diagrammatic cylindrical section of a nozzle structure em bodying my invention, the passages being brought into the same-horizontal plane; Fig. 2 is a view of a modified form of nozzle partition, and Fig. 3 is a radial "sectional view of a part of a nozzle diaphragm and the adj acent blade or bucket wheels.

Referring to the drawing, 5 indicates a series of nozzles which are defined by inner and outer walls 6 and 7 and nozzle plates or partitions 8, and 9 indicates a ring of rotary buckets or blades to which the nozzles discharge elastic fluid. The elastic fluid enters the nozzles as indicated by the arrow X and is directed by the nozzles against the blades or buckets 9, the direction of rotation being that indicated by the arrow Y. In the following specification 1 term the nozzle-deconstructed and shaped that a fining surface 10 the rear wall of the nozzle and the nozzle-defining surface 11 the front wall of the nozzle. I

Accordin to my invention I provide a nozzle whic is wholly'converging and is so ressure is caused to exist in the nozzle just efore and directly adjacent the end of the rear wall of the nozzle which pressure is higher than the back pressure or counter pressure. The por tion of the .nozzle just before and directly adjacent the rear wall of the nozzle is indicated at 12 in the drawing. Usually a nozzle embodying my invention will converge quite rapidly and the'pressure throughout the exit end or cross section will be substantially uniform and higher than the back pressure. By exit end or cross section I mean the plane between the nozzle partitions at the exit end normal to the stream, Such lane being indicated by the dotted line A.

otted line A indicates also the width of the throat of the nozzle which may be defined as the shortest distance between adjacent nozzle partitions. It' will be understood that by back pressure or counter pressure I mean the ressure at the entrance edge of the ring 0 blades to which the nozzle is dischargin For best results the pressure in the nozzlb just before the end of the rear wall should'exceed that of the back pressureby about twenty per cent, but it will be understood that this value may be more or less without departing from my'invention.

The maximum decrease in pressure which can be obtained by expanding an elastic fluid in a wholly converging nozzle is about 0.46; that is, with the maximum expansion obtainable in a wholly converging nozzle the discharge pressure will be about 0.54of the initial pressure. This is known as the critical pressure. The critical pressure varies somewhat with variations in steam conditions and nozzle efiiciencies but for any fixed conditions is a constant. My invention may be carried out by utilizing a wholly converging nozzle which will expand the elastic fluid down to'the critical pressure and employing a back pressure a suitable amount lower than the critical pressure, or it may be carried out by utilizing a wholly converging nozzle which will expand the elastic fluid down to a pressure higher than the cutical pressure and employing a back pressure a desired amount lower than this; In such a case the back pressure may be equal to or greater than the critical pressure. For best results, I preferably. employ a back pressure higher than the critical pressure and awholly conver ing nozzle which will expand the elastic flui down to a pressure a suitable amount higher than such back pressure.

According to the arrangement shown in the drawing, I make the nozzles wholly converging and shaped so that the elastic fluid, when it reaches the exit end of the nozzle guide blades, is not completely expanded down to a pressure equal to the back pressure. For example, the nozzles may be so shaped that the elastic fluid will be only about 80% expanded in them. As a result the pressure-at the exit end of each nozzle and hence that which exists directly adjacent and just before the end of the rear wall of the nozzle will exceed the back pressure by a predetermined amount.

Viewed from another as ec-t my invention comprises the provision o elastic fluid turbine nozzles having what I term zero throats or negative throats. Heretofore, in non-expansion nozzles it has been considered necessary to have a parallel portion preceding the exit of the nozzle for the purpose of guiding the stream and giving the stream the right direction before it leaves the constraining walls of the nozzle. This portion is generally called the throat of the nozzle and I term a nozzle so constructed as a nozzle having a positive throat.

I have discovered that such a guiding portion is not necessary to secure proper direction of the exit stream and that the front wall of the nozzle from the throat to the exit is in reality the true guiding element by virtue of the fact that the instant the stream tends to leave this guidingsurface a region of lower pressure is formed on the guiding surface which tends to restore the stream to the guiding surface and makes it 7 exit from the nozzle at the proper angle.

Accordin to 'my'invention as viewed from this aspect, provide non-expanding nozzles in which the parallel portions are eliminated and I then rely upon the following tail portion or front wall of the nozzle to guide the stream and reduce the angle of discharge to the final proper angle for striking the buckets. Considering my invention from the aspect of a nonexpansion nozzle having a guiding parallel portion, when this guiding para lel portion is just eliminated a nozzle is provided in accordance with my invention, having what I term, zero negative throat. However, I have found it advantageous not only to eliminate the parallel portion but also to cut off the exit ends of the plates at a considerable distance before the point is reached at which the parallel portion just tends to be formed, and nozzles so formed may be considered as having a greater or lesser amount of negative throat length according to the distance which the plates terminate before the point is reached at which the parallel portion will tend to be formed.

A nozzle embodyin my invention may be defined mathematica ly as one which is wholly converging and wherein the following relationship holds:

A:or (P .sine aT) Where A is the shortest distance between adjacent nozzle partitions; i. e., the throat width.

P is the distance between similar points on adjacent nozzle partitions; i. e., the pitch of the nozzle partitions.

T is the thickness of the exit edge of the "partitions and 'ais the angle of the front wall of the partition with respect to the plane of the diaphragm.

By actual tests on nozzles embodying my invention I have been able to abtain nozzle efficiencies substantially higher than have heretofore been considered possible. These gains in efliciency I believe are due to the followm Between the exit ends of the nozzles of a turbine and the inlet edges of the rotating blades, or buckets, there is always a clearance which may be of the order of 0.20 in. for example, and it willbe clear that there are spaces represented by continuations of the guide blades up to the entrance edges of the buckets to which no elastic fluid passes directly from the nozzles. In the drawing, these spaces are represented by the areas contained within the dotted parallelograms 13. Now, with my improved form of nozzle, when the elastic fluid leaves the ends of the guide blades, since it has not been already expanded down to the counter pressure, it continues to expand and as a result more or less completely, fills the areas 13 so that there is a substantially continuous solid stream of elastic fluid entering the buckets. As a result losses due to eddies in the elastic fluid after it leaves the nozzles are practically eliminated and a substantially solid, contlnuous stream of elastic fluid is presented to the rotating blades. Furthermore, my invention results in the use of shorter nozzle partitions which cuts down the frictional loss and lends itself to the use of nozzle partitions having a minimum of thickness at their edges. This decrease in frictional loss is due not only to the shorter length of nozzle partitions but also to the fact that the elastic fluid flows along them at a lower yelocity, the lower velocity being due to the incomplete expansion in the nozzles. The

meters density is greater but the additional frictional loss due to the eater density is more than offset by the ecrease in frictional loss due to the lower velocity.

In connection with the expansion of the elastic fluid into the spaces represented by the parallelograms 13 it will be clear that one of the essential things is that the pressure existing adjacent to the rear walls 10 of the nozzles just before their exit ends should exceed the back pressure, and it: is not necessarily required that the pressure throughout the plane of the exit ends of the nozzles should exceed theback pressure or that it should be uniform although this is usually the case. This result may in some cases be obtained by nozzle structures other than those which are wholly converging and viewed from certain aspects my invention comprehends any nozzle structure wherein with a back pressure higher than the critical pressure the nozzle is shapedtofgive a pressure under the guide blades just before their exit ends which exceeds the back pressure. Such an arrangement will eflect the expansion of the elastic fluid into the spaces 13 after it leaves the nozzles. I prefer, however, an arrangement wherein the nozzles are wholly converging because this results in the use of shorter nozzle partitions-and hence cuts down the frictional loss due to the elastic fluid flowing along their walls.

In some cases the exit edges may be beveled as shown at a in Fig. 2 in which case 'I is taken as the thickness of the plates projected to the lane of the exit substantiall as shown in ig. 2.

As stated above, it has heretofore been zles, to have a parallel portion preceding the exit of the nozzle to guide the stream and give it the right direction, and in such nozzles the stream is discharged at a right angle to the plane of the throat. In other words, the stream leaves the nozzle in the same direction as when it leaves the throat. With nozzles embodying my invention, the stream, while it leaves the narrowest section of the nozzle at a right angle thereto and at a certain angle with the plane of'the diaphragm, is so directed by the front wall of the nozzle that its angle is changed arid the final angle at which it strikes the moving blades referred to the plane of the diaphragm is less than the angle of exit from the narrowest section. This is illustrated in 'Fig. 1, where the arrow B indicates the direction of exit from the throat and 1) indicates the angle with the plane of the diaphragm, and the arrow C indicates the direction at which the stream strikes the moving blades and the angle a the angle with the plane of the diaphragm. As will be seen from this, the elastic fluid is discharged from the narrowest section at a greater angle with the plane of the diaphragm than the final angle with which it strikes the moving blades.

What I claim as new, and desire to secure by Letters Patent of the United States,

1. A. nozzle diaphragm having nozzle par;- titions so spaced and formed that wholly converging, non-expanding nozzles are pro vided in whichthe ratio of the throat width increased b the thickness of the exit edge of the partltions to the pitch of the nozzle partitions is equal to or greater than the sine of the angle which'the front walls of the nozzle partitions make with the plane of the diaphragm.

2. In anelastic fluid turbine, a rotor having blades thereon, and nozzles comprising a ring of guide blades for directing elastic fluidtheretmsaid nozzles being so shaped that the total actual smallest discharge area is greater than the area of the annular ring multiplied by the sine of theangle of the discharge of the guide plates, and the product diminished by the sum of the projected area of the late edges. I

3. In an e astic fluid turbine, a rotor having blades thereon, and nozzles comprising guide blades for directing elastic fluid thereto, said nozzles being so shaped that on any cylindrical section'through the nozzles the width of the narrowest section of the stream is greater than the product of the distance between similar points on the nozzle partitions and the sine of the exit angle of the partitions diminished bythe projected thickness of the exit end of the partition.

4. In an elastic fluid turbine, a rotor havin blades thereon, and nozzles comprising guide blades 101 directing elastic fluid thereto, said nozz es being so shaped that the elastic fluid is discharged from the narrowest section at a greater angle with the plane of thediaphragm than the final angle with which. it strikes the movin blades.

5. In an elastic fluid turbine, a rotor having blades thereon, and nozzles comprising guide blades for directing elastic fluid there to, said nozzles being wholly converging and converging at such ara-tethat the pressure of elastic fluid existing adjacent the rear walls of the nozzles just before their exit ends, exceeds the back pressure.

6. In an elastic fluid turbine, a nozzle structure in which the nozzles are wholly converging and in which they converge at such a rate that the elastic fluid in passing through them is only expanded down to a pressure a predetermined amount higher than the back ressure.

7. An elastic uid turbine comprising rows of blades and nozzle structures for directing elastic fluid against them characterized by the fact thatfthe nozzles are wholly con- 9, In an elastic fluid turbine, a rotor havin blades thereon and nozzles for directing elastic fluid thereto,there being a clearance space between the exit ends of the nozzle partitions and the blades, said nozzles convergingat such a rate that with a back pressure on the nozzles greater than the critical pressure, incomplete expansion is effected in the nozzles, the remainder of the expansion taking place in the space between the exit cross sections of the nozzles and the entrance edges of the blades.

10. In an elastic fluid turbine, a nozzle ring having nozzles converging at such a rate that with a back pressure on them equal to or greater than the critical pressure,-elastic fluid in passing through them will be expanded down only to a pressure a predetermined amount higher than the back pressure.

11. An elastic fluid turbine having wholly converging nozzles,.said nozzles converging at such a rate that with a back pressure on them at least equal to the critical pressure, the elastic fluid will be expanded only about 80% in the nozzle portion preceding the exit plane.

12. An elastic fluid turbine having nozzles which converge at such a rate that the pressure on the concave side of the exit end of the nozzle partition is higher than the back pressure, whereby the space following the partition will be filled with elastic fluid.

13. An elastic fluid turbine comprising a rotor having one or more rings ofblades thereon and nozzles for directing elastic fluid to the blades, there being clearance spaces between the exit ends of the nozzle partitions and the blades, 0 aracterized by the fact that the nozzle passages have such a contour that the elastic fluid is incompletely expanded in them and issues from them at such a pressure as to cause the elastic fluid discharging from them to fill such clearance spaces.

In witness whereof, I have hereunto set my hand this 11th da of Jul 1922.

HARRISO LORI G WIRT.

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