US3865506A - Centrifugal compressor - Google Patents

Abstract

A centrifugal compressor having a relatively low flow rate of less than 400 cfm at 4-6 psi comprises a housing enclosing a backward-bladed shaft mounted, motor driven impeller. The impeller blades have the configuration of air foils gradually increasing in width from their inlet tip to a point beyond the mid-length and then decreasing in width toward their discharge tip to define air flow channels between adjacent blades and the width of the channels increases linearly from the inlet end to the discharge end as a function of the channel length. The blades have a flat upper surface covered with a diffuser plate. The air flow channels discharge into a diffusion chamber which communicates with an annular pressure chamber surrounding the air inlet to the compressor, the walls of the pressure chamber defining an air nozzle to the air inlet. Auxillary vanes are positioned in the discharge end of the air flow channels.

Description

Gerlach CENTRIFUGAL COMPRESSOR [75] Inventor: C. Richard Gerlaeh, San Antonio,

Tex.

[73] Assignee: Micro-Gen Equipment Corporation. San Antonio, Tex.

[22] Filed: July 9, 1973 [21] Appl. No.: 377,567

[52] U.S. Cl. 415/213 R, 416/185 [51] Int. Cl. F04d 7/02 [58} Field of Search... 415/204, 206, 213 R, 219 C; 416/183, 184,185,186

[56] References Cited UNITED STATES PATENTS 45,398 12/1864 Durall 415/213 R 350,362 10/1886 Hawley 415/213 R 2,046,226 6/1936 Weightman et al. 415/213 R 2,715,814 8/1955 Barr 415/219 A 2,753,808 7/1956 Kluge 416/183 2,907,278 10/1959 Emerick 415/206 3,489,340 l/l970 l-lolzhausen.. 415/204 3,788,765 l/l974 Rusak 415/213 R FOREIGN PATENTS OR APPLICATIONS 830,542 2/1952 Germany 415/147 Feb. 11, 1975 Primary ExaminerHenry F. Raduazo Attorney, A gent, or F irm Donald R Comuzzi. Ted D. Lee

[57] ABSTRACT A centrifugal compressor having a relatively low flow rate of less than 400 cfm at 4-6 psi comprises a housing enclosing a backward-bladed shaft mounted, motor driven impeller. The impeller blades have the configuration of air foils gradually increasing in width from their inlet tip to a point beyond the mid-length and then decreasing in width toward their discharge tip to define air flow channels between adjacent blades and the width of the channels increases linearly from the inlet end to the discharge end as a function of the channel length. The blades have a flat upper surface covered with a diffuser plate. The air flow channels discharge into a diffusion chamber which communicates with an annular pressure chamber surrounding the air inlet to the compressor, the walls of the pressure chamber defining an air nozzle to the air inlet. Auxiliary vanes are positioned in the discharge end of the air flow channels.

5 Claims, 4 Drawing Figures pinto-p /IIIAL\\\\\ ////l K'JEHTEQ FEB] 1 I975 SHEET 3 OF 3 FIG.

1 CENTRIFUGAL COMPRESSOR BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to dynamic'type air compressors and more particularly to a centrifugal compressor or blower that will obtain low air flow output in the 5-6 psi range with relatively high efficiency and low manufacturing cost.

2. Prior Art Prior art compressors are generally not efficient for economical use in the 5-6 psi range with relatively low flow rates.

Small positive displacement blowers have been designed for use in delivering low flow rates, however, these units have not been particularly successful due to the high cost of manufacturing and relatively low effi ciency which is inherent in this type of compressor. The most common blower for such use is a rotary, twoimpeller blower which employs two symmetrical figureeight shaped impellers rotating in fixed relationship with each other. Timing gears are necessary to position the impellers accurately in relationship to each other thus increasing the cost of manufacture. Another disadvantage is the necessity of operating this type of blower at very high speeds to obtain maximum volumetric efficiency due to constant slip loss.

Low flow rates as used herein refers to flow rates in the below 400 cfm range. Likewise, compressor efficiency is defined as the hydraulic horsepower out of the compressor divided by the input horsepower into the power unit driving the compressor. Hydraulic horse power is the product of the pressure and flow rate of the air out of the compressor. Input horsepower is de' fined as the shaft horsepower out of the power unit.

Dynamic-type compressors have also been considered for use in low air flow range. These are compressors in which air or gas is compressed by the mechanical action of rotating vanes or impellers imparting velocity and pressure to the flowing air. Dynamic-type machines are inherently high speed machines which perform to best advantage and with greater efficiency for large capacity requirements. The axial flow dynamie-type compressor is best suited for the very high air flow requirements and the centrifugal flow compressor is more economical at the lower flow rates. Of course, even the lower flow rates for which centrifugal compressors are normally considered are substantially above that contemplated in the present invention. As a rule of thumb, the minimum discharge flow rate for a centrifugal compressor is generally considered to be 400 cfm.

There are many. advantages to using a centrifugal compressor for low air flow requirements, a very important one being the low manufacturing cost. Other advantages will become apparent in the following discussion.

The impeller of a centrifugal compressor imparts energy to the flowing air by means of centrifugal force. The impeller consistsof a number of blades rotating on av shaft. The blades are either open type, or are mounted on a hub disc or positioned inside a housing to provide air passages fromthe air inlet at the center of the impeller to the air. outlet at the outer periphery of the impeller. The impeller blades are either straight or curved blades and extend either radially from the center toward the outer periphery of the impeller or extend at an angle to the radius and away from the direction of rotation. The latter type being generally referred to as a backward-bladed impeller and the blades may be either curved or straight. The blade design determines to a large extent the capacity and pressure range of the compressor and is therefore the most complex component in the compressor.

The principal of the operation of a centrifugal compressor requires that the air be pulled into the rotating blades toward the center of the impeller and accelerated to high velocity and then the velocity must he reduced significantly to convert the kinetic energy to static energy and increase the pressure. A controlled deceleration of the air flow is essential in order to avoid high energy losses in the conversion phase.

Deceleration of the air flow is accomplished by increasing the cross-sectional area of the air-flow channels toward the outer periphery of the impeller. The deceleration is accomplished by the air-flow channel configuration which is determined by the design of the blades.

The known types of centrifugal compressors are de signed for high volume air flow and controlled deceleration is obtained by contouring the upper edge of the blades with rather complex surface contours which are expensive to manufacture. Of course, the expense is not so critical in a large capacity compressor.

Due to the increasing need for a low volume air compressor operating at relatively low pressures, it became an object of this invention to provide a low volume compressor that will overcome many of the problems encountered in the prior art.

It is a primary object of this invention to provide a centrifugal compressor having a novel impeller design suitable for delivering a relatively low volume of air (below 400 cfm) in the 5-6 psi range with reasonable efficiency.

More particularly, it is an object of this invention to provide an impeller with novel vanes in the shape of air foils and which avoids the need for complex upper edge blade contours.

It is still another object of this invention to provide a low volume compressor that can be manufactured very economically.

SUMMARY OF THE INVENTION The invention consists of a centrifugal compressor having a two section housing surrounding an impeller. A diffuser plate is constructed as an integral part of one section of the housing and is positioned to define a diffuser passage or chamber surrounding the circumferential edge of the impeller.

The diffuser passage communicates with an annular chamber or accumulator for collecting the pressurized air. The accumulator is positioned circumferentially around the front of the compressor and surrounds the air inlet to the impeller, the inner circumferential wall of the accumular defining an inlet nozzle to the air inlet. Air outlet ports or nozzles are provided in the accumulator to discharge compressed air from the accumulator.

In order to accomplish the primary objective of this invention, namely to obtain low air-flow volumes (below 400 cfm) at 4-6 psi, it is necessary to reduce the combined cross-sectional area of all the air-flow channels. This must be accomplished in such a manner as to reduce friction losses and manufacturing costs. If prior art practices were employed, impeller blade heights would be reduced to reduce the cross-sectional area of the air passages and the upper surface contour of the blades would have a complex configuration to decelerate air flow with the attendant high cost of manufacture. Of greater concern, however. is the low hydraulic efficiency of such a design for low volume flow. This low efficiency results from the large increase in the wetted area" of the impeller air passages or channels in relation to the air flow volume. The wetted area" being the area around the periphery of the channel which produces skin friction with the flowing air.

The impeller blades of this invention have been designed to reduce the wetted area in relation to the cross-sectional area of the channel. Furthermore, the upper surface of the blades are designed to eliminate the complex upper surface contour.

The impeller is provided with novel air foil blades or vanes with a straight upper surface contour. The air foil blades are backward-bladed, that is, they are installed at an angle to the impeller radius and away from the direction of rotation. The inlet tip of the vanes are substantially tangent to the air inlet and intersect the radius at an angle of approximately 30 at the discharge tip. The vanes are shaped like air foils increasing in width from the inlet tip and discharge tip toward the middle.

The impeller is mounted on a rotating drive shaft which extends through the rear compressor housing section. The shaft has means for connecting to a suitable power source such as an electric motor or internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective front view with a partly cut section, of the compressor of this invention.

FIG. 2 is an exploded perspective rear view of the compressor.

FIG. 3 is a perspective view of the impeller.

FIG. 4 is a cross-section view of the centrifugal compressor of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The centrifugal compressor of this invention consists of an impeller 2 enclosed between a back housing section 11 and a front housing section 31.

The back section consists of a rear wall 12 and a forwardly extending circumferential side wall 13. The rear wall 12 has a hub portion 14 extending rearwardly therefrom and surrounding a shaft bore 15.

Positioned within the bore 15 are sutable antifriction bearings which are identified as a front bearing 17 and rear bearing 18 held in spaced relationship by a sleeve 19 mounted around a drive shaft 22 and inside the bore 15. A spacing sleeve 20 is positioned inside the bore 15 and frictionally engages front bearing 17 and the impeller 2. Concentric with and rotatably surrounding the spacing sleeve 20 is a seal ring 21. Interposed between the seal ring 21 and the bearing 17 is a snap ring 16 to take the forward thrust of the bearing 17.

The drive shaft 22 extends through the bore 15 and is rotatably mounted in the bearings 17 and 18. In the embodiment depicted in the drawings, the shaft 22 has a belt sheave portion 23 positioned on the outside of the hub portion 14. A shoulder 24 on the sheave portion 23 abuts the rear bearing 18.

The impeller 2 consists of a circular disc' 3'with a hub portion 4 integral therewith, said hub portion having an axial bore 5 extending therethrough' for receiving the drive shaft 22. The hub portion 4 is mounted 'on the front of the disc 3 and extends axially therefrom. A cover plate 25 is mounted over the hub 4 and may be formed integral with the hub 4 or fastened thereto by welding. An air inlet zone 40 on the front of the disc 3 extends radially from the hub portion 4 to the inlet tip of air foil vanes 6 and 6, said air foil vanes defining air flow channels 7 and 7' therebetween. The impeller is preferably formed as an integral casting of suitable material such as a rigid plastic or metal.

The air foil vanes 6 and 6 extend from the outer circumference of the air inlet zone 40, outwardly to the outer periphery of the impeller disc 3. The vanes 6 and 6' are substantially tangent to the outer circumference of the inlet zone 40 at their inlet tips and extend outwardly therefrom and away from the direction of rotation, at an angle to the impeller radius.

The air foil vanes have a substantially flat upper surface and are substantially straight along their one side from the inlet tip to the discharge tip, the other side being substantially convexly curved from the inlet tip to the discharge tip thus providing a vane of increasing width from the inlet tip along its length to a point beyond the midlength and then decreasing in width to the discharge tip. A portion of the convexly curved side may be flattened for economy in machining. The air flow channels 7 and 7 defined by adjacent air foil vanes 6 and 6' increase gradually in width from near the air intake end to the discharge end. The immediate air intake end of alternate channels 7 may be slightly widened to facilitate air intake. Likewise, alternate air foil vanes 6' are shorter than the adjacent air foil vanes 6 to define air inlet pockets 9 at the inlet to adjacent channels 7 and 7 to facilitate the intake of air into the air flow channels 7 and 7. The width of the channel increases linearly as a function of the channel length.

This gradual increase in channel width produces a substantial linear deceleration of the air flow thereby converting the kinetic energy of the air to static pressure.

A short substantially constant width secondary vane 8 is mounted near the outer periphery of the disc between each pair of air foil vanes 6 and 6. These short vanes 8 are positioned in the discharge end of the air flow channel to break up the formation of eddies or vortexes in the flowing air prior to entry into the diffusion passage 42.

The drive shaft 22 has an elongated portion extending through the axial bore 5 in the disc 3. A threaded bore 23 extends axially into the elongated shaft portion and receives a threaded bolt 24 which extends through a hole in hub cover 25. A washer 26 may be positioned between the head of bolt 24 and the cover 25.

Front housing section 31 has a front wall portion 32 connected to the front edge of the circumferential side wall 13 of the back housing section 11 and extending radially inwardly therefrom to integrally connect to an axially extending circumferential wall portion 33. The circumferential wall portion 33 is connected to a diffuser plate 34, said diffuser plate being substantially parallel to the front wall portion 32. The front housing section 31 is mounted over the front of the impeller means 2 with the front wall portion 32 being connected to the side wall 13 of the back housing section 11 by means of suitable fastening means such as bolts 35 extending through a bore 36 in the front wall portion 32 and into threaded bore 37 in the side wall 13 to define an annular pressure chamber 41.

The diffuser plate is positioned adjacent and parallel to flat upper surface of the air foil vanes 6 and 6' to en close air flow channels 7 and 7. An air intake opening 38 is provided in the center of the diffuser plate 34 to permit air to be pulled into the compressor by the impeller 2. The circumferential wall portion 33 of front housing section 31 defines an air inlet nozzle 39 directing air to the air inlet opening 38.

The diffuser plate 34 is spaced from the rear wall 12 and side wall 13 of the back housing section 11 to provide a diffusion chamber or passage 42. The air flow channels 7 and 7 discharge air into the diffusion chamber 42 for final conversion of the kinetic energy into static pressure before the air enters the annular pressure chamber 41. As can be seen from the drawings, the diffusion chamber 42 communicates with the pressure chamber 41 around the entire periphery of chamber 41.

Compressed air is discharged from the pressure chamber 41 through suitable discharge openings such as opening 44 extending through the front wall 32 of front housing section 31. While only one such discharge opening has been depicted, it will be understood that any desired number may be provided from the pressure chamber 41. Furthermore, the discharge opening may be provided in either side wall 13 or front wall 32.

Having thus described the preferred embodiment of my centrifugal compressor wherein flow has been restricted to a relatively low volume by the novel air foil vane design, reference is now directed to the appended claims for a definition of the scope of my invention.

I claim:

1. A centrifugal air compressor comprising a housing enclosing an impeller, an air inlet in said housing to the air inlet zone of said impeller, said impeller having a plurality of circumferentially arranged air foil vanes extending outwardly from said air inlet zone at an angle to the impeller radius and opposite the direction of rotation, said air foil vanes gradually increase in circumferentially width from the inlet tip to beyond their mid length and then decrease in circumferentially width to the discharge tip, said air foil vanes have a free flat upper surface adjacent the housing, adjacent air foil vanes define an air flow channel therebetween, said channel gradually increasing in width from near the air intake end to the air discharge end, said width increasing linearly as a function of the channel length, said air inlet zone of said impeller being at the center portion thereof and said air foil vanes are substantially tangent to the outer circumference of said air inlet zone. the length of alternate air foil vanes is less than the adjacent air foil vane to define an air inlet pocket at the inlet to each pair of adjacent air flow channels.

2. The apparatus of claim 1 wherein an auxillary vane of substantially constant width is positioned in the discharge end of each air flow channel.

3. The apparatus of claim 2 wherein the compressor housing comprises a front housing section and a back housing section, the back housing section consists of a rear wall with a central bore receiving an impeller drive shaft, and a forwardly extending circumferential sidewall connected to the front housing section, said impeller being rotatably mounted on said drive shaft, said front housing section consists of a front wall portion connected to the front edge of the circumferential sidewall of the back housing section and extending radially inwardly therefrom to engage and connect to an axially extending circumferential wall portion, said axial extending circumferential wall portion being connected to a diffuser plate at right angles thereto, said diffuser plate enclosing the front surface of the impeller and extending parallel to said impeller vanes and spaced a small distance therefrom, said diffuser plate having an air inlet opening in the center portion thereof.

4. The apparatus of claim 3 wherein said front housing section and said circumferential sidewall of said back housing section encloses an annular pressure chamber positioned forwardly of said diffuser plate, said diffuser plate and said back housing section defining a diffusion chamber around the outside periphery of said impeller, said diffusion chamber communicating with said pressure chamber.

5. The apparatus of claim 4 wherein the axially extending circumferential wall portion defines an air inlet nozzle surrounding the air inlet opening in said diffuser plate, and wherein said pressure chamber has at least one discharge opening therefrom.

Claims (5)

1. A centrifugal air compressor comprising a housing enclosing an impeller, an air inlet in said housing to the air inlet zone of said impeller, said impeller having a plurality of circumferentially arranged air foil vanes extending outwardly from said air inlet zone at an angle to the impeller radius and opposite the direction of rotation, said air foil vanes gradually increase in circumferentially width from the inlet tip to beyond their mid length and then decrease in circumferentially width to the discharge tip, said air foil vanes have a free flat upper surface adjacent the housing, adjacent air foil vanes define an air flow channel therebetween, said channel gradually increasing in width from near the air intake end to the air discharge end, said width increasing linearly as a function of the channel length, said air inlet zone of said impeller being at the center portion thereof and said air foil vanes are substantially tangent to the outer circumference of said air inlet zone, the length of alternate air foil vanes is less than the adjacent air foil vane to define an air inlet pocket at the inlet to each pair of adjacent air flow channels.

2. The apparatus of claim 1 wherein an auxillary vane of substantially constant width is positioned in the discharge end of each air flow channel.

3. The apparatus of claim 2 wherein the compressor housing comprises a front housing section and a back housing section, the back housing section consists of a rear wall with a central bore receiving an impeller drive shaft, and a forwardly extending circumferential sidewall connected to the front housing section, said impeller being rotatably mounted on said drive shaft, said front housing section consists of a front wall portion connected to the front edge of the circumferential sidewall of the back housing section and extending radially inwardly therefrom to engage and connect to an axially extending circumferential wall portion, said axial extending circumferential wall portion being connected to a diffuser plate at right angles thereto, said diffuser plate enclosing the front surface of the impeller and extending parallel to said impeller vanes and spaced a small distance therefrom, said diffuser plate having an air inlet opening in the center portion thereof.

4. The apparatus of claim 3 wherein said front housing section and said circumferential sidewall of said back housing section encloses an annular pressure chamber positioned forwardly of said diffuser plate, said diffuser plate and said back housing section defining a diffusion chamber around the outside periphery of said impeller, said diffusion chamber communicating with said pressure chamber.

5. The apparatus of claim 4 wherein the axially extending circumferential wall portion defines an air inlet nozzle surrounding the air inlet opening in said diffuser plate, and wherein said pressure chamber has at least one discharge opening therefrom.

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