USRE13665E - Centrifugal compressor - Google Patents

Description

i s. A. Moss. UENTBIIUGAL COMPRESSOR.

Reissued 1160.30, 19'1'3. 1 3,665.

APPLIOA-TIUK FILED DBO. l, 1918.

Inoenbor:

Sanomlfl.' Moss. B )KM UNITED stra'rns SANFORD A. Moss,

intrinrr OFFICE.

0F LYNN, MASSACHUSETTS, ASSIGNOB, TO GENERAL ELECTRIC COMPANY, A. CORPORATION OF NEW YORK'.

onN'rnIrUGAL COMPRESSOR.

Original No. 1,075,300,

1913. serial no. comes.

To all whom 'it may concern Be it known that l, SANFORD citizen of the United States, residing at Lynn, county of Essex, State of Massachusetts-have invented certain new and useful Improvements in Centrifugal Compressors, of which the following is a specification.

The present invention has for its object to improve the eiiiciency and construction of centrifugal compressors, as Will be more fully set forth hereinafter.

In carrying out' my invention a oompressor having one, two or more stages is provided. When it is desired to furnish air or other gas at relatively high pressure, the discharge conduit of one compressor or stage is connected to the inlet conduit of an other compressor or stage, and so on. When it is desired to iurnih compressed air or otherl gas at relatively low pressure but in relatively large ipantities, the stages of the compressor may e arranged -to discharge in multiple. The rotary elements may all be mounted on the same or ,different shafts, and be driven by` one or more sources of power. The construction of the compressors is similar except that the cross-sectional area of the working passages, or passages `between Vthe blades in the rst or low pressure compressor, is somewhat greater than that of the passages in compressor, the cross-sectional area of the passages in the succeeding compressors gradually decreasing as the pressure of the fiuid increases. Each revolving element is mounted on a suitable shaft, supported in one ormore bearings in the 'com ressor casing or on separate supports. T .e said element is provided with a number of radial vanes or blades having sharpened ends arranged to properly receive and discharge the fluid undergoing compression. As the element rotates, the air or other elastic flu-id is discharged outwardly, due to centrifugal force. The blades or varies mounted on the impeller may be closed in at the sides by plates which rotate therewith, or the Walls of the stationary casingv may be employed to complete the sides of the air-conveying passages. When the former arrangement is provided the clearances between the rotating and stationary walls of the casing should be small, and preferably means employed to The direction or keep down the leakage.

A. Moss, aA

the second or higher pressurev angle of entrance of the air or gas to be compressed into the Wheel or impeller is an important feature. The fluid should be delivered to the rotating blades or vanes in a plane at right angles, orI substantially so, to the axis of rot-ation. To accomplish this, stationary directing vanes are employed which extend toward a corn-mon point at their receiving end, and at their discharge ends are situated in close-proximity to the receiving ends of the rotating blades.. I the inipeller speed is such that the pressure accruing through the conversion of velocity into pressure is less than twice the pressure at the periphery of the impeller, the nozzle required to properly bring the air to rest will b e wholly divergent, considered from the impeller outward. In this case the pressure variation is so slight that the specific volume does notchange greatly. If however the iin-peller `speeds are very high, then the pressure due to the conversion of the velocity muy be suoli that the pressure in the scroll or discharge conduit is more than twice the pressure atthe periphery of the impeller. In such cases the nozzle, to properly bring the air to rest, must first converge and late-r diverge. This is due to the. fact tha-tin the anterior or converging portion or" the nozzle the velocity does not decrease very rapidly, While, on the contrary, the pressure increases rapidly. In order to take care of the decrease in velocity only, the nozzle should diverge, but owing to the fact that the increase in pressure is accompanied by' a decrease in volume, provision must be made therefor by making the anterior portion of the nozzle converge. To state the matter in a diilerent way, the velocity decreases so slowly compared to the reduction in volume due to the increase in pressure that the anterior portion or the nozzle must gradually reduce in cross-sectional area. In the posterior or diverging portion of the nozzle thew'velocity decreases very rapidly, and in order to'rnake provision for this the walls must diverge very rapidly. In this portion therefore the contraction of the air due to increase of pressure does not exercise a@ very marked' inilucnce. Therefore, in order to make the proper provision for both the velocity action and the contraction action, the posterior portion of the nozzle must be wholly divergent. The nozzle may 'i tant .internal construction; Fig. 3 is a Idivided. into sections the separate streams of fluid delivered from` the vane spaces will' 'be received by it and the velocity at once convertedinto pressure. Itwill be seen that the conversion from velocity toA pressure takes place immediately after the maximum vvelocity is created instead ofat some disciency. When a compressor 'or' a' 'stageof a multi-stage compressor is`- intended to produce only a relatively small increase in pressure, it is unnecessary to provide the nozzle withv converging Walls on, the receiving or anterior portion, but where higher pressures are `to be produced 'it isnecessary, in order to obtain the Ibest results, 4to use them. yThis applies whether the nozzle is subdivided into sections ornot. Y Surrounding the nozzle andformed in the casin or otherwise suitably "supported and connected, is a scroll or discharge :pipe 'which gradually increases in cross-sectional area to'iaccommodatethe -increased amount of .fluid due to the amounts dischargedjby the vanev spaces; "The-crosssectional area of the scroll pipe vshould be such as to retain the fluid in its compressed state. Y.

In the accompanying drawings, which illustrate certain embodiments of the invention, Figure 1 is a view in elevation of a centrifugal air compressor with certain of the parts broken away to show the construction of the vanes and nozzle; Fig. 2 is a view taken at right angles to that of Fig. 1, with certain of the parts broken away to show the diagram representing the velocities of the fluid passing throughthe passages between the directing vanes, and also the velocity of the tluid passing thro-ugh the vane spaces on the rotating element; 4 is a detail view of a packing employed lvbetween the rotating and stationary parts.; Fig. 5 shows the invention applied to a multi-stage compressor having two or more stages; Fig. 6 is a detail view of a nozzle having converging and diverging p ortions; Figs. 7 and 8 are diagrammatic '.vlews of impeller blades and velocity diagrams, and Fig. `9 is an enlarged view of the i nozzle shown in Fig; 1.

The casing for the compressor is made up of two ' principal parts 1 and 2 which are flanged and secured 4together by the bolts 3.

4 represents themainshaft, which is supi ported-'in a suitable bearing 5 and carries the revolving-element 6. The revolving ele- ,of the rotating element.y

eddies, etc.

object in` curving these vanes at vthe ends is to cause them to receive and discharge the a1r or other fluid at the most effective angle. The sidesof the vanes are covered by plates or walls9 and 10, Fig. 2,- which serve to con fine thetluid undergoing compression in the separate vane spaces. However I may omit these wallsand have the vanes extend to the casing. The wall 9 formsla continuation of `thefsupporting hub and itxmayormay notbe formed integral therewith. The Wall 10 may with the vanes or be at- Y be formed integral ytached `thereto with suitable bolts or other retaining devices. It is provided with an enlarged central opening,\ concentric f'with' the axis .of rotation, Within which are locatedpthe directing vanes 11 and theshieli 12. '.The shield is conical in form and, as

shown, covers the end of the shaftl and hub The directing vanesvll, at theirV receiving ends, form an angle of about 45 with the axis .of rotation, while the' dischar'geends are parallel with the shaft' and are surrounded by .the inner ends of the blades on the rotating e-lement. By means of this construction the incoming uid is prevented from strikingthe rotating part of the wheel or impeller until it is delivered toA the vanes 8,`which, by their centrifugal action, simultaneously increase the velocity and pressure of the fluid. In the particular compressor shown in Figs. 1 and 2, approximately one-'half of the pressure of the fluiddischarged is due to the centrifugal. action of the wheel itself, and the rej-.malnder to the action of the nozzle.

f The vanes 11, the

shield 12, and the flange 130ie the part 2 should be as smooth as possible in order to permit the airI toy freely enter the vane spaces in the rotating element, and this without undue losses due to To the ange 13 of 'the casing isbolted a flange 14 whichreceives Fthe screw-threaded end of the conduit 15. The conduit 15 ma be lconnected with any suit able source "ofy supply, such `as the atmoa. phere, a tank or the discharge end of aother compressor. l y

I have found in actual practice that in some cases there is a tendency for-,the Huid passing through the vane spaces to leak he` tween the' wall 10 and the revolving lelement and the casing, and re'enter the vane spaces.` If this leakage is excessive, a packing may be employed, such as shown in Fig. 4, wherein 1G. represents cylindrical extension of the casingto willichthe stationary directing vanes are attached, and 17 the hub-like portion on the right hand'side, Fig. 2, of the rotating element. Between the parts 16 and 17 a chambery is formedtoreceive the soft rpacking 18, which is adjusted by means of' bolts 1,9.

The parts of themain casingy are provided suitable gland and adjusting mees `rotating element is converted into pressure.

These passages extend taugentfially or substantialiy sorto the-path of the outer ends of the moving vancs. The passages between the partitions should be relatively long with respect tio their width so asto properly direct the fluid particles, and also to cause the fluid to be compressed as it asses through them. By this I mean that t e distancebetween the dotted'i linev 40' of Fig. 9-v and the dotted line 41is much great-er than the distance between the side walls measured at any point in a plane erpendicular to the direction of the flow o? the fluid. The portion 42 of the nozzle between thel sharpened inlet edges of the partitions serves to collect or gather the fluid particles preparatory to discharging them` into the nozzle proper. The effective action of the nozz-le in compressing the fluid, reducing its velocity to a negligible amount and increasing its temperature and density takes place in the nozzle between the dotted lines 4() and 41.

In Fig. 3, 24 of the larger diagram represents the absolute velocity of the air at the point of'entrance tothe nozzle Wit-h respect to earth; 25 the velocity of the wheel; and 26 the relative velocity of the air passing through the Wheel. Referring to the smaller diagram of Fig. 3, 27 represents the absolute velocity of the fluid entering the wheel; 28 the velocity of the Wheel at the point of ent-rance; and 29 the relative velocity of the air with respect to the vanes 8. The fluid discharged by the nozzle or nozzle section is collected inthe scroll pipe 30 which is formed in the casing. This scroll pipe radually increases in cross-sectional area groin one end to the other, and finally termi nates in a flanged conduit 31, always, however, retaining the fluid in its compressed slate.

Referring to Fig. 5, two air compressors or stages 32 and 33 are shown, which are alike in all substantial respects. 32 represents the nrst or low pressure compressor, and 33 represents the second or higher pres sure compressor. The compressor 82 receives air or other fluid from the conduit in the salue manner as is shown-in Fig. The fluid discharged therefrom is collected in the scroll ipe andis'discharged into the conduit 34, tie latter being connected with the inlet of the compressor 33. Between each two compressors I may employ an intercooler 35 of suitable construction to re- .duce the temperature of the air or other gas undergoing compression. .The present intercooler comprises a casing containing gascarrying tubes, and pipes conveying a cooling flu-id to and away from the casing. I may employ a greater number-of stages in the air compressors andi between some or all of the stages intercoolers may be provided.

In. Figs. 1= and 2' a nozzle is shown Awhich is wholly divergent. This is suitable for comparatively low impeller speeds. In order to-have exactly the same nozzle action iior great impeller speeds, ainozzl'e first convergent and then divergent should be substitut-ed, as shown in Fig. 6.' I therefore do not limit myself in this particular, and use that form of nozzle which calculation andI experiment show is best suited for each case. .This nozzlev is not provided with partitions as shown in- Fig. 1, but they may be' provided if desired. To state this matter in another Wa.` I have found that a compressible fluid discharged from an impeller and compressed by a certain amount due to centrifugal action, and at a certain temperature 'Ils due to this compression, and with a certain velocity V3 due to part of the energy input o impeller can be further compressed by means of a stationary nozzle as already described` if the cross section of the stream is properly varied in the direction of flow of the fluid along it. I have found that there is a certain critical velocity, Vc, which can be computed according to the formula- Vc \/gcRT3 VczCritical velocity ft. per sec.

gzAcceleration due to gravity, ft. per sec. per sec.

RIGas constant in well known formula per-RT Where j) is in lbs. per sq. ft., 'v is in cu. ft. per lb. and T is absolute Fahr. temperature. Y'

kIRatio of specific heats at constant. pressure and constant volume.

Taz-Abs. Fahr. temperature at impeller ex-it.

In cases where it` is desirable to make the impeller exit velocity V3 in ft. per second greater than the critical velocity Vc as above computed a nozzle is provided which will conduct the stream so thatits cross section is first gradually decreased until a point is reached where the velocity has been reduced to the critical velocity. There will be a certain amount of compression produced by the flow along the nozzle to this point beyond that produced by the impeller. The nozzle is arranged so as to gradually increase the cross section of the stream beyond this point. There is ,thereby produced further compression. In cases where. it is desirable to make the impeller exit velocity V3 in feet per second, less than the critical` velocity Vc as above computed there is provided a, nozzle which will conduct the stream l 'so that its cross section is always gradually .25 the impeller will be very great. On the conincreased. This compresses the fluid beyond vthe amount accomplished by the impeller.. In all cases it is assumed that the impeller' wheel Areceives the air at a point of comparat-ively small diameter and discharges it at a point o f greater diameter. The exact ratio of diameters is not essential. By having the inner diameter of the wheel at the point where the air is received 'of a greater or less `ratio to the outer diameter, the relative de. l gree of compression due to centrifugal action and to nozzle action is altered. I' therefore do not limit "myself'to anyfparticular ratio -of diameters. The compression-due to een?i trary, if the angles areas indicated by S, the velocity V of the air leaving thewheel will bemuch less. That is to say,'the

pressure due-to nozzle action will be much greater for the arrangement shown in Fig. 7 than for the arrgngemnt .shown in Fig. 8. -In-"'Figs7"ad'8, W of the larger diagrams indicates the velocity ofthe impeller, V 'the absolute velocity of the air leaving 4the impeller, and R the velocity of the air relative to the impeller. The difference in the rela-*1` density before discharging it, and a conduit" tive velocity indicated by V andv R in the two figures is due to the curvature at the .discharge-ends of the vanes. In the smaller diagram, W indicates `the velocity of the receiving ends of the impellerA vanes relatively to the stationary guide vanes, V the absolute velocitydof the air leaving the guide vanesand entering the impeller, and R the j relative velocity of the air with, respect to the guide vanes. The smaller diagrams in Figs. 7 and`8 represent the velocity\ of the air passingv through the .directing van-es.

Various relative effects can be secured by 1various other combinations of angles of the .'.Yinlet gnide'and of the beginning and end of f so the impel-ler vanes,and I dol not, herejfore, limit myself in ,this particular. n Fig. 7 the velocity ofthe air relative ,to the impeller. is shownto beY the same/at the entrance and exit. This is adconji'plished by having the ltotal area.,of. the ,passages by which the air.leaves the Whefl somewhat smaller than the passages by which it enters,

' to make up forfthe contraction due tothe increase in presenti@ from centrifugal action, yHowever, other combinations vare .po'sslble` or instance, the passages land vane angles may be so arranged that the air enters the :racers impeller wheel-at a great velocityv and leaves ciple of operation ot' my invention, together with the apparatus which I'now consider to represent the best embodiment thereof; but

I, desireto have it understood. that the ap-f'so paratus shown lis only illustrative, ,and that the invention 'can be carried* out in other Ways.

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

1: In ay centrifugal compressor for elastic uids, the combination of a casing, a rotating -impeller mounted therein whichis rovided with radially disposed vanes havlng outwardly diverging passages between them, whichvvanes and passages` confine the fluid and simultaneously impart velocity to the fluid and compress it by reducing its volume, directing vanes arranged to direct the incoming fluid against the inner ends .of the impeller vanes, an annular nozzle losurrounds the outer ends of the vanes` and is provided `with 4tangential. partitions and Walls that decrease the velocity of the luid to a predetermined small amount, and also further decrease the volume and increase its that surrounds the nozzleand receives Huid from it and retains the same in its compressed state;l f v2. -In a centrifugal compressbr, the combination of a rotating element which is pr- -vided' with vanes shaped to simultaneously impart velocity tothe luidand compress it, directing vanes which directthe incoming Huid against the inner enxdsov the vanes on the rotating element ina..direction perpendicular to 'the axis of rotation, a shield which assistsin directing the incoming fluid" 115 and prevents it from striking that portion of the Wheel within the Ainner ends of the vanes, a nozzle whichA surrounds the outer ends of the vanes and isvprovidedV with walls that decrease the lvelocity of and also the '120 volume of the fluid and increase its densitys and temperature, and a\ discharge conduit which receives fluid directly from the nozzle and retains it in its compressed state. Y

'3. In a centrifugalcompressor for elastic 1 5 Huid, the Yco y bination offan impeller which ispro.v detl ihthjradia'l passages thatA gradually increase incross-sectional area` toward the point of discharge and simultaneously impart velocity to the fluid and'compress it, 139

leasing for thefimpeller, any'annular nozzle that closely surrounds theV impeller, is vlocated in theplan'e thereof and' receives the elastic fluid discharged by it, thin partitions the nozzle that extend tangentially ktoward -the periphery of the impeller and form passages of definite size and .shape for directing the fluid streams, the said passages enlarging gradually on the discharge sides by an amount sufficient to lreduce the velocity of the flui'd to a small value, at the same time compress it and increase its density, which compression is added to that due to the impeller, a conduit that surrounds the no 'zzlean'd receives the fluid from all I' said passages and holds it in acompressed state, and a means for reducing the tendency of the fluid to cause eddies asl it enters the impeller. u Y

4. Inaicentrifugal compressor, the combination of a rotary vane-carrying element, a

. casing therefor, means for directing the incoming fluid into the receiving ends of the vane spaces of the rotating element, an annular nozzle, Which surrounds the rotating element and is located in the plane of said element, straight Walled partitions in the nozzle extending in the direction of flow of the fluid to form passages, each passage being provided With a restricted throat and posterior diverging Walls Which com ress the fluid and reduce the velocity there-o and increase its densityrand temperature prior to discharging it, a plurality of means that cooperate with the rotary vanes to direct the incoming fluid thereto, and a conduit which receivesthe fluid after it is discharged by t the passages, at the same time preventing it from expanding.

, 5. In a centrifugal compressor, the combination of a rotating element, vanes or blades thereon Which extend radially and have their ends curved forward to discharge the fluid with high velocity relative to the impeller, stationary vanes for directing the passage of fluid into the vane spaces of the rotating element, which are also curved at the ends, the discharge ends of the directing vanes being surrounded by thev receiving ends of the rotating vanes, a nozzle having a passage Which expands from the throat tothe discharge end, and a conduit receiv- -ing fluid from the discharge end of the nozzle.

(l. In a centrifugal compressor, the com.

said nozzle having divergingside Walls and straight sid'ed tangential partitions tof-form passages each with a restricted inlet and an enlargedbutlet, the `length of the passage beings( considerably greater than the Width at any point measured in a 'planeperpendicular tothe direction of flovv of' the fluid so that the fluid will be compressed in the passage, Willhave-its velocit-y reduced to a predetermined small amount and its temperature increased, a casingl for theV nozzle and impeller, and an inlet and an outlet.

8. In a centrifugal compressor, the combination of a casing, a rotating impeller mounted therein and having radially disposed vanesfshaped simu taneously impartrvelocity to an elastic, flui and compress it by centrifugal force and to' discharge'it peripherally with the velocity and reduced volume unimpaired into the nozzle, an annular nozzle that surrounds the impeller and receives the fluid directly from it, said nozzle having partitions extending in the general direction of rotation and in the plane of the impeller which form tangentially arranged definite passages that receive fluid from the impeller, and are of properly varying cross-section in the direction of their length to diminish the velocity of the fluid'.

as received from the impeller and cause additional compression and discharge the same with a relatively lovsr residual velocity, a conduit means common to the said nozzle passages that receives the fluid and retains it in its compressed'state, and a discharge conduit.

9. VIn a centrifugal compressor for elastic fluids, the `combination of a casing, a rotating impeller mounted therein having vanes With passages between them shaped to decrease the velocity of the elastic fluid relative to the impeller and cause compression of the fluid in' addition tothe compression caused by lthe centrifugal action of the said impeller, an annular nozzle that surrounds the impeller in the plane thereof, and has a passage of properly 'varying cross-section in the direction of the stream lines, said nozzle receiving and directing the fluid, di-

minishing its velocity and causing additional compression and discharging it With u a relatively loW residual velocity, a conduit receiving the fluid from the nozzle, and a second conduit which supplies the fluid to the inlet ends of the impeller vanes.

l0. In a centrifugal compressor for elastic fluids, the combination of a casing, a rotating impeller mounted therein and having vanes for compressing and imparting velocity to the elastic fluid, said. vanes receiving fluid at their inner ends and discharging it outwardly, a driving shaft for the impeller,'

an annular nozzle into which the impeller discharges which has a passage of properly varying cross-section in the direction of the stream lines with its largest cross-section `at .tlie' point of final discharge, said nozzle receiving, guiding and directing the elastic fluid from the impeller and also compressing anddischarging it Withr'relatively low residual velocity,V andmeans for conveying' elastic fluid to the inlet ends o f the vanes.

11. In a compressor for elastic fluids, ythe combination cfa casing, a rotating impeller mounted therein and-having vanes for compressing and imparting velocity to the elastic fluid, a driving' shaft for the impeller, anannular nozzle into which the impeller discharges throughout its entire'circumference, said nozzle having a passage which is wholly divergent in the direction of the stream lines with its largest crosssection at the point of {inal discharge, and receiving, guiding and directing the elastic vfluid received from the impeller and also SANFORD MOSS.

Witnesses JOHN A. MoMANUs, Jr.,

DUGALD MDK. MCKILLOP.

Images