Multi-Stage Compressor with Internal Interstage Feed

Abstract

A multi-stage compressor where the refrigerant is transferred from stage to stage internally. The compressor uses a first stage impeller mounted on a first end of motor shaft and a second stage impeller mounted on a second end of the same motor shaft. The motor shaft and both impellers rotate in unison. Refrigerant discharged from the first stage impeller is transferred to the intake of the second state impeller through passages within the compressor itself.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of devices that pressurize a working fluid. More specifically, the invention comprises a multi-stage compressor with an interstage feed system that is internal to the compressor's housing.

2. Description of the Related Art

The inventive compressor can be used in a wide variety of applications—with heating, ventilation, and air conditioning (“HVAC”) systems being a good exemplary application. The invention is well suited for use in HVAC systems for large structures (high-rise buildings, civic arenas, and the like). Knowing how a compressor is used in such a system will benefit the reader's understanding. Accordingly, a basic description of such a system is provided—though the reader should bear in mind that the inventive compressor is by no means limited to use in such systems.

FIG. 1 provides a simplified depiction of a large HVAC system 10. The system includes three main loops—cold water loop 32, refrigerant loop 36, and hot water loop 20. Cold water loop 32 and hot water loop 20 are typically connected to liquid-to-air heat exchangers located throughout the structure. As an example, if cooling is needed, control valves direct the flow of cold water within cold water loop 32 through a liquid-to-air heat exchanger that is part of an air handler in a particular zone within the structure. The circulating cold water cools air that is forced through the liquid-to-air heat exchanger by a blower. The cooled air is then fed through air ducts and distributed into the zone via air registers. Likewise—if heating is needed in a particular zone—control valves direct the flow of hot water within hot water loop 20 through a liquid-to-air heat exchanger for that zone.

Those knowledgeable in the field will recognize that the cold and hot water loops of FIG. 1 are depicted in a very simplified form. Such loops often contain multiple pumps on multiple floors, along with many control valves and branch lines. These features are omitted in FIG. 1 for purposes of visual clarity. In the simplified depiction, a single pump 30 forces water around cold water loop 32 as indicated by the arrows. A single pump 22 forces water around the hot water loop as indicated by the arrows.

The compressor or compressors force circulation within refrigerant loop 36. The operation of the refrigerant loop will be explained by following a volume of refrigerant as it travels around the loop. At Point A, the refrigerant is in a low-pressure gaseous state. It is drawn into the intake of first stage compressor 12, where it is compressed to an intermediate pressure and discharged into interstage line 16 (Point B). This refrigerant at an intermediate pressure is fed by interstage line 16 into the intake of second stage compressor 14 (An economizer inlet 62 is also provided in interstage line 16—the purpose of which will be explained subsequently). Second stage compressor 14 further compresses the gaseous refrigerant. The refrigerant emerges as a hot, high-pressure gas at Point C.

The hot gas next enters condenser 18—in this example a liquid-to-liquid heat exchanger. Heat is transferred from the refrigerant circulating in refrigerant loop 36 to the water circulating within hot water loop 20. The refrigerant leaves condenser 18 as a much cooler gas (Point D)—and may in fact be a mixture of gaseous and liquid refrigerant at this point. The cooled refrigerant then passes through economizer 24. The economizer is another heat exchanger. The refrigerant traveling from Point D to Point E surrenders additional heat in the economizer so that the refrigerant is a high-pressure liquid by the time it reaches Point E.

After Point E the refrigerant flows into branch 63. One path leads from branch 63 to economizer 24. The other branch leads to evaporator 34. The branch leading toward the economizer takes the high-pressure liquid refrigerant to expansion valve 26. Expansion valve 26 expands the liquid refrigerant to an intermediate pressure gas. This phase change drops the temperature of the refrigerant. The cooler gaseous refrigerant then passes through economizer 24 on its way to economizer inlet 62 on interstage line 16.

The second path leaving branch 63 proceeds to expansion valve 28. Expansion valve 28 expands the high-pressure liquid refrigerant to a low-pressure state. This phase change drops the temperature of the refrigerant as it passes through evaporator 34. Evaporator 34 is of course another heat exchanger. The cold refrigerant within evaporator 34 absorbs heat from the water circulating within cold water loop 32. The gaseous refrigerant leaving evaporator 34 returns to Point A, where the cycle repeats.

The presence of an economizer is optional. They are commonly used in HVAC systems for large buildings because they increase the overall cooling capacity of the system, and this helps the system accommodate extreme cooling loads. The presence of an economizer also tends to reduce overall efficiency, however. For this reason, not all systems include an economizer.

Since the refrigerant loop 36 depicted in the system of FIG. 1 does include an economizer, three distinct pressure zones exist within the loop. A high-pressure zone exists from the exit of second stage compressor 14 to the expansion valves 26,28. An intermediate-pressure zone exists between expansion valve 26 and the intake side of second stage compressor 14 (including interstage line 16). A low-pressure zone exists from the output side of expansion valve 28 to the input side of first stage compressor 12.

In all these zones some flow-induced pressure losses will occur. But these will be small in comparison to the pressure differences between the zones themselves. For example, the pressure at Point E will be somewhat less than the pressure at Point C. However, the drop will be minimal in comparison to the pressure difference between the three zones.

The reader should also bear in mind that the terms high-pressure, intermediate-pressure, and low-pressure are intended to describe relative pressures within the system, rather than a reference to a pressure outside the system—such as ambient atmospheric pressure (commonly considered to be 1013 millibars, 760 mm of mercury, 29.92 inches of mercury, or 14.7 psi). As a first exemplary embodiment, the low-pressure portion of the system may have a pressure that is greater than ambient atmospheric pressure. As a second exemplary embodiment, the low-pressure portion of the system may have a pressure that is less than ambient atmospheric pressure. As a third exemplary embodiment all three pressure zones may have a pressure that is less than ambient atmospheric pressure.

Hot water loop 20 circulates heat where it is needed and also serves to remove heat from the overall system when that is needed. Hot water loop 20 transports the hot water leaving condenser 18 to another heat exchanger—such as cooling tower 24. Cooling tower 24 transfers the heat within hot water loop 24 to air outside the building. Such cooling towers are often located on the roof of a building.

Evaporator 34 is often contained within a unit known as a “chiller.” The term “chiller” is commonly used because its main purpose is to chill the water circulating within cold water loop 32. A chiller contains the heat exchanger serving as evaporator 34, and often contains one or more pumps and control valves as well.

The present invention relates to a multi-stage compressor such as used in the exemplary system of FIG. 1. Prior art systems have often used two separate compressors to create the multiple stages or a single compressor having two compression stages. There are many prior art examples of such multi-stage compressors.

FIG. 2 depicts a first prior art example of a multi-stage compressor. Two stage compressor 40 includes a first stage impeller 42 and second stage impeller 48 attached to a first end of motor shaft 54. In this example the two impellers spin at a common speed. Motor 55 drives motor shaft 54 to a desired and controlled speed. The motor shaft 54 is supported by two or more sets of bearings 57. The motor in this example is a homopolar motor supported by magnetic bearings. Such a motor and bearing arrangement is described in more detail in prior U.S. Pat. Nos. 5,857,348 and 7,240,515 to Conry (the present inventor), which are hereby incorporated by reference. Housing 56—which is depicted simplistically—houses the motor, motor shaft, and other associated hardware.

The two impellers must be enclosed within suitable housings to direct the flow of the refrigerant gas they are compressing. Inlet 44 ducts the inlet gas into first stage impeller 42. Transfer passage 46 takes the output from the first stage impeller and transfers it to the input for second stage impeller 48. Outer volute 50 collects the refrigerant gas as it exits the second stage. The gas then exits the compressor through outlet 52.

The reader will note the presence of economizer inlet 62 in transfer passage 46. Referring back to the flow diagram of FIG. 1, the reader will note the location of economizer inlet 62 between the two stages of the compressor/compressors. For a single compressor having multiple stages—as shown in FIG. 2—it is necessary to provide an economizer inlet 62 between the stages.

Looking still at FIG. 2, those skilled in the art will realize that the spinning impellers impart a tractive force—sometimes known as a thrust force—on motor shaft 54. This tractive force urges the motor shaft in the direction indicated by the arrow. It is necessary to provide a substantial thrust bearing 53 to resist this tractive force. The presence of the thrust bearing adds friction and reduces overall efficiency.

FIG. 3 depicts another prior art two-stage compressor 58 with a structure configured to balance the thrust forces and eliminate the need for a significant thrust bearing. In this design first stage impeller 42 is affixed to a first end of motor shaft 54 and second stage impeller 48 is secured to the second end of the same motor shaft. The two impellers spin at the same speed in the same direction, so the blades of the two impeller must be inclined in opposite directions.

Inlet 44 ducts the low-pressure refrigerant gas into first stage impeller 42. Outer volute 49 collects the gas compressed by the first stage impeller and directs it into interstage transfer pipe 60. Interstage transfer pipe 60 carries the refrigerant to the input side of second stage impeller 48. Outer volute 50 collects the gas leaving second stage impeller 48. Outlet 64 carries the compressed gas away from the compressor. Economizer inlet 62 is provided in interstage transfer pipe 60.

In studying the compressor of FIG. 3, those skilled in the art will realize that the two impellers produce tractive forces that oppose each other (as indicated by the two arrows shown along motor shaft 54). Such a compressor can be designed so that the opposing tractive forces very nearly cancel out. Perfect cancellation is not possible for all speeds, but the need for a large thrust bearing is eliminated in this design and overall friction is reduced. However, the presence of the large interstage transfer pipe 60 existing outside of the compressor housing introduces additional undesirable losses.

It would be preferable to provide the advantages of a compressor with balanced tractive forces for the impeller stages but without incurring the flow losses of an external transfer pipe between the stages. The present invention provides such a design.

BRIEF SUMMARY OF THE PRESENT INVENTION

The present invention comprises a multi-stage compressor where the refrigerant is transferred from stage to stage internally. The compressor uses a first stage impeller mounted on a first end of motor shaft and a second stage impeller mounted on a second end of the same motor shaft. The motor shaft and both impellers rotate in unison. Refrigerant discharged from the first stage impeller is transferred to the intake of the second state impeller through passages within the compressor itself.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic view, showing a prior art HVAC system for a large structure.

FIG. 2 is a sectional elevation view, showing a first type of mirror art multi-stage compressor.

FIG. 3 is a sectional elevation view, showing a second type of prior art multi-stage compressor.

FIG. 4 is a sectional elevation view, showing a first embodiment of the inventive compressor.

FIG. 5 is a sectional elevation view, showing a second embodiment of the inventive compressor.

FIG. 6 is a sectional elevation view, showing a third embodiment of the inventive compressor.

FIG. 7 is a perspective view, showing an exemplary exit region for an embodiment of the inventive compressor.

FIG. 8 is an elevation view, showing an exemplary exit region for an embodiment of the inventive compressor.

FIG. 9 is a sectional elevation view, showing details of the second stage transfer passages.

FIG. 10 is a sectional elevation view, showing details of the outlet transfer passages.

FIG. 11 is a sectional perspective view, showing still another embodiment of the inventive compressor.

FIG. 12 is a perspective view, showing a housing for the embodiment of FIG. 11.

FIG. 13 is a perspective view, showing a stator tube for the embodiment of FIG. 11.

FIG. 14 is a perspective view, showing a stator tube for the embodiment of FIG. 11.

FIG. 15 is a perspective view, showing a second stage diffuser support for the embodiment of FIG. 11.

FIG. 16 is a perspective view, showing a second stage diffuser support for the embodiment of FIG. 11.

FIG. 17 is a perspective view, showing an intermediate connector for the embodiment of FIG. 11.

FIG. 18 is a perspective view, showing an intermediate connector for the embodiment of FIG. 11.

FIG. 19 is a perspective view, showing a second stage labyrinth for the embodiment of FIG. 11.

FIG. 20 is a perspective view, showing a second stage labyrinth for the embodiment of FIG. 11.

FIG. 21 is a perspective view, showing a second stage inlet vane plate for the embodiment of FIG. 11.

FIG. 22 is a perspective view, showing a second stage inlet vane plate for the embodiment of FIG. 11.

FIG. 23 is a perspective view, showing a second stage inlet vane for the embodiment of FIG. 11.

FIG. 24 is a perspective view, showing a second stage inlet vane for the embodiment of FIG. 11.

FIG. 25 is a perspective view, showing an outlet diffuser for the embodiment of FIG. 11.

FIG. 26 is a perspective view, showing an outlet diffuser for the embodiment of FIG. 11.

FIG. 27 is a perspective view, showing a diffuser housing for the embodiment of FIG. 11.

FIG. 28 is a perspective view, showing a diffuser housing for the embodiment of FIG. 11.

FIG. 29 is an elevation view, showing the compressor of FIG. 11.

FIG. 30 is an elevation view, showing the compressor of FIG. 29 installed for use in a conventional HVAC system.

FIG. 31 is a simplified elevation view, showing the compressor of FIG. 29 installed in an unconventional HVAC system.

FIG. 32 is a sectional elevation view, showing yet another embodiment of the inventive compressor.

REFERENCE NUMERALS IN THE DRAWINGS

• • 10 HVAC system
  • 12 first stage compressor
  • 14 second stage compressor
  • 16 interstage line
  • 18 condenser
  • 20 hot water loop
  • 22 pump
  • 24 economizer
  • 26 expansion valve
  • 27 conduit
  • 28 expansion valve
  • 30 pump
  • 32 cold water loop
  • 34 evaporator
  • 38 economizer inlet line
  • 40 two-stage compressor
  • 42 first stage impeller
  • 44 inlet
  • 46 transfer passage
  • 48 second stage impeller
  • 49 outer volute
  • 50 outer volute
  • 52 outlet
  • 53 thrust bearing
  • 54 motor shaft
  • 55 motor
  • 56 housing
  • 57 bearing
  • 58 two-stage compressor
  • 60 interstage transfer pipe
  • 62 economizer inlet
  • 63 branch
  • 64 outlet
  • 66 compressor
  • 67 outer volute
  • 68 internal passage
  • 70 second stage transfer passage
  • 72 second stage inlet
  • 74 outer volute
  • 76 outlet transfer passage
  • 78 outlet
  • 80 cooling inlet
  • 82 cooling outlet
  • 84 cooling flow
  • 88 motor cavity
  • 86 central axis
  • 92 end casing
  • 94 axial bearing
  • 96 magnetic thrust bearing
  • 98 housing
  • 100 motor support
  • 101 flange
  • 102 foil bearing
  • 104 stator tube
  • 106 magnet
  • 108 through bolt assembly
  • 110 second stage diffuser support
  • 111 flange
  • 114 intermediate connector
  • 116 second stage labyrinth
  • 118 economizer inlet
  • 120 second stage labyrinth tube
  • 122 axial bearing
  • 124 second stage inlet vane plate
  • 126 second stage inlet vane
  • 128 outlet diffuser
  • 130 diffuser housing
  • 132 vane
  • 134 guide vane
  • 136 guide vane
  • 138 outer surface
  • 140 inner surface
  • 142 cooling outlet
  • 144 radial passage
  • 146 exit surface
  • 147 flow gap
  • 148 entrance surface
  • 150 mounting hole
  • 152 flow gap
  • 153 guide vane
  • 154 exit surface
  • 156 entrance surface
  • 158 flow gap
  • 160 exit surface
  • 162 entrance surface
  • 164 flow gap
  • 166 exit surface
  • 168 flow gap
  • 170 exit channel
  • 172 exit
  • 173 entrance surface
  • 174 entrance surface
  • 175 interstage flow
  • 176 flow gap
  • 177 second stage inlet flow
  • 178 exit surface
  • 179 second stage exit flow
  • 180 second stage impeller housing
  • 181 second stage impeller recess.
  • 182 entrance surface
  • 183 outside radius fillet
  • 184 flow gap
  • 185 inside radius fillet
  • 186 mating surface
  • 187 intake interface
  • 188 mating surface
  • 189 intake interface
  • 190 flow gap
  • 191 guide vane
  • 192 mating surface
  • 194 channel
  • 196 mating surface
  • 198 flange
  • 200 flange
  • 202 exit surface
  • 203 entrance surface
  • 204 guide vane
  • 206 outer volute
  • 208 flange assembly
  • 210 flange
  • 212 economizer manifold
  • 214 evaporator-to-compressor line
  • 216 compressor-to-condenser line
  • 218 economizer-to-compressor line
  • 220 micro chiller
  • 222 housing
  • 224 bulkhead
  • 226 bulkhead
  • 228 heat exchanger
  • 230 heat exchanger
  • 232 cold water loop
  • 234 hot water loop
  • 236 outlet transfer passage

DETAILED DESCRIPTION OF THE INVENTION

The following descriptions pertain to several exemplary embodiments of the proposed invention. Many other embodiments and combinations of embodiments will occur to those skilled in the art. The scope of the invention is accordingly much broader than the exemplary embodiments described.

FIGS. 4-6 illustrate simplified embodiments of the present invention. More operationally realistic embodiments are disclosed subsequently. FIG. 4 provides a sectional elevation view for compressor 66. The components of the compressor lie along central axis 86. In the example shown, inlet 44 and outlet 78 both lie along central axis 86, though this will not always be the case. As for prior art compressors, low-pressure refrigerant gas is drawn in through inlet 44, compressed by the compressor, and discharged through outlet 78. Axial bearings are used to support and stabilize the rotating motor shaft—thereby greatly reducing friction losses. In the example of FIG. 4 a single motor 55 is used to spin a single motor shaft 54. First stage impeller 42 is mounted on a first end of motor shaft 54—proximate inlet 44. Second stage impeller 48 is located on a second end of motor shaft 54—proximate outlet 78. The two impellers in this embodiment therefore spin in the same direction and at the same rotational velocity. The vanes of the two impellers are pitched oppositely, with the result that the tractive forces induced by operation largely cancel each other out. Some residual tractive force will remain, and a small thrust bearing is preferably provided to balance this tractive force. However, the use of the opposed impellers eliminates the need for a large thrust bearing.

The impeller configuration shown in FIG. 4 is known in the prior art—such as the example of FIG. 3. However, unlike the prior art, the refrigerant gas transferred between the first and second stage impellers in this inventive embodiment travels within the compressor itself—rather than through an external pipe. Refrigerant flowing out of first stage impeller 42 is collected in outer volute 67. The flow is then directed along internal passage 68—which generally flows outside the perimeter of motor 55 but inside the compressor's exterior housing 56. The flow continues within internal passage 68 until it reaches the vicinity of second stage impeller 48.

Refrigerant flow in the vicinity of second stage impeller 48 becomes more complex. Second stage transfer passages 70 receive the flow from internal passage 68 and turn the flow approximately 180 degrees so that the flow enters second stage inlet 72. In this disclosure the term “approximately 180 degrees” shall mean between 120 and 210 degrees, inclusive. Outer volute 74 receives the discharge flow from second stage impeller 48. Outlet transfer passages 76 take the flow from outer volute 74 and feed it to outlet 78. The passages 70,76 depicted overlap in a complex arrangement that will be described in more detail subsequently. End casing 92 is optionally provided to enclose all the passages 70,76 within a continuous exterior housing.

Thus, the reader will appreciate in the embodiment of FIG. 4 that the refrigerant passes through both compressor stages without traveling outside the compressor. Further, the reader will note how this exemplary arrangement places the inlet 44 and outlet 78 in a line—along central axis 86.

Motor 55 generates heat while operating. Some of the refrigerant flow can be channeled around or through the motor to provide adequate cooling. FIG. 5 depicts an embodiment similar to FIG. 4, but with added cooling features. Cooling inlets 80 divert some of the refrigerant flowing within internal passage 68 into motor cavity 88. The refrigerant flows around and through the motor stator (cooling flow 84) before exiting through cooling outlets 82. The exiting refrigerant flows back into internal passage 68 and on to the second stage impeller.

FIG. 6 shows a second approach to the problem of cooling the motor—using return flow from an economizer circuit. FIG. 1 shows the overall design of an HCAC system 10 using an economizer 24. The reader will recall that the flow downstream of expansion valve 26 passes through economizer 24 and returns via economizer inlet 62 to a point between the two compressor stages. Returning now to the example of FIG. 6, the reader will note the location of economizer inlet 62. Economizer inlet 62 receives the partially expanded refrigerant and feeds that flow into motor cavity 88. The refrigerant flow circulates around the motor cavity before exiting through coolant outlets 82, where it rejoins the interstage flow in interior passage 68 traveling toward the second stage impeller. The refrigerant flowing through the motor cavity serves to cool the motor.

Returning now to FIG. 4, the flow of refrigerant through this exemplary embodiment of the inventive compressor will be summarized. The refrigerant flows through inlet 44 and through first stage impeller 42. The refrigerant is collected in outer volute 67 and flows through a 90-degree transition into internal passage 68. Internal passage carries the refrigerant past the motor and to the start of second stage transfer passages 70. Second stage transfer passages 70 bend the flow through approximately 180 degree before delivering the refrigerant to second stage inlet 72. Second stage impeller 48 completes the compression of the refrigerant gas and delivers it to outer volute 74. Outlet transfer passages 76 carry the fully compressed refrigerant gas from outer volute 74 to outlet 78.

In looking at the flow paths leading into and out of the second stage impeller, it is apparent that the passages must pass close to each other without actually intersecting—since the flow paths contain refrigerant at different pressures. The physical interrelationship between second stage transfer passages 70 and outlet transfer passages 76 is complex and can be physically realized in multiple ways. FIGS. 7-9 depict an exemplary physical realization. The example of FIGS. 7-9 is convenient to visualize and understand. However, it is not necessarily practical for manufacturing. A more complex design intended for practical manufacturing will be described subsequently.

FIG. 7 provides a perspective view of the flow paths proximate outlet 78. Multiple second stage transfer passages 70 carry refrigerant coming from internal passage 68. Passages 70 are spaced in a radial array around the perimeter of the compressor housing. These transfer passages 70 redirect the flow through a roughly 180-degree transition and into the inlet of the second stage impeller.

Outer volute 74 collects the compressed refrigerant leaving the second stage impeller. Multiple outlet transition passages 76 carry the discharge refrigerant to outlet 78. As the reader will note in FIG. 7, each outlet transfer passage 76 passes through a gap between adjacent second stage transfer passages 70.

FIG. 8 provides an end view of the assembly of FIG. 7. The reader will note how second stage transfer passages 70 and outlet transfer passages 76 are both arranged in radial arrays about the compressor's central axis. The reader will also note how the passages 70,76 travel through the required pathways without interfering.

In order to further clarify the relationship between the passages 70,76, FIG. 8 includes “call outs” for sectional views provided in FIG. 9 and FIG. 10. FIG. 9 provides a sectional elevation view through two of the second stage transfer passages 70. In this simple embodiment, internal passage 68 is an annular passage just inside housing 56. The two second stage transfer passages 70 shown in the section receive the flowing refrigerant gas from internal passage 68, smoothly reverse the direction of flow, and feed the flow to the intake of second stage impeller 48. The multiple passages 70 merge into a single passage proximate the intake. Second stage impeller 48 further compresses the refrigerant and discharges it to volute 74.

Returning now to the end view of FIG. 8, the reader will note that the section for FIG. 10 is taken through two of the outlet transfer passages 76. FIG. 10 shows how two outlet transfer passages 76 take the refrigerant flow from volute 74 and direct it to outlet 78. The multiple passages 76 merge proximate the outlet 78.

The embodiment thus depicted in FIGS. 7-10 is one that performs the objectives of the invention and one that can be physically realized. It is not altogether practical, however. The interleaved construction depicted in FIG. 7 is reminiscent of known internal combustion engine intake and exhaust systems. These are often complex weldments—requiring expensive and complex components as well as considerable skilled labor. Such an assembly can also be produced by casting—though this is again a relatively labor-intensive process. It is preferable to provide embodiments using components that are easily mass produced and that are more amenable to factory assembly using unskilled or semi-skilled labor.

The embodiments of FIGS. 4-10 serve best to illustrate the general operative concepts of the invention. The embodiment of FIGS. 11-28 represents a commercially practical version of the invention. The operative concepts are essentially the same, but the physical construction is quite different.

FIG. 11 shows a sectional elevation view through a commercially practical embodiment. This view is helpful in describing the location of the components with respect to each other. This disclosure provides many additional views of the individual components found in the assembly of FIG. 11. It is advisable to follow these descriptions by looking at the views of the individual components to understand their structure in detail and looking at the overall view provided in FIG. 11 to understand how the components interrelate.

Compressor 66 depicted in FIG. 11 has its components arrayed along a central axis 86 running through the motor shaft that mounts the first and second stage impellers. The flow enters through inlet 44, flows through the compressor, and exits through outlet 78.

The term “interstage flow” in this disclosure means the refrigerant flow between the first and second stage impellers. It may include economizer return flow. It may also include some cooling flow for the motor or other components (such as motor power supply components). The term “second stage exit flow” means the refrigerant flow between the second stage impeller and outlet 78.

Directional terms in the description of the embodiment of FIG. 11 are defined with respect to inlet 44 and outlet 78. The term “inlet direction” means toward the inlet 44 and the term “outlet direction” means toward the outlet 78. “Inlet side” means the side of a component that is nearer the compressor inlet. “Outlet side” means the side of a component that is nearer the compressor outlet. “Inward” means toward central axis 86. “Outward” means away from central axis 86

Compressor 66 shown in FIG. 11 has essentially the same flow path for the refrigerant as depicted for the embodiments of FIGS. 4-10. Refrigerant flows through inlet 44 to first stage impeller 42. First stage impeller 42 compresses the refrigerant and discharges it to outer volute 67, where it flows into internal passage 68 within housing 98.

The flow of the internal passage becomes quite complex as it passes through multiple components. This complex flow path will be explained subsequently. However—while still looking at FIG. 11—the interstage flow from volute 67 to second stage inlet vane plate 124 follows a path that is generally parallel to central axis 86. Once the interstage flow passes second stage inlet vane plate 124 it is redirected into the inlet of second stage impeller 48—a course reversal of approximately 180 degrees. The flow leaving the second stage impeller is again redirected to pass through outlet diffuser 128 and exit through outlet 78. The reader will thus perceive that the overall flow path for the embodiment of FIG. 11 is analogous to that depicted in FIG. 4.

Before describing how the internal components create the desired flow path in the embodiment of FIG. 11, some other significant features of the assembly will be described. The external housing in this example is created by an assembly of three components. Housing 98 and diffuser housing 130 each include an upstanding flange. Second stage labyrinth 116 contains a corresponding flange 101. These three flanges are configured to mate. They can then be rigidly connected by any suitable means—including an array of bolts, brazing, gluing, threading, etc. From the vantage point of FIG. 11, assembly is accomplished by moving housing 98 from left to right and moving diffuser housing 130 from right to left—with these two components meeting at flange 101 of second stage labyrinth 112.

Motor shaft 54 is aligned with central axis 86. Motor 55 resides within motor cavity 88—surrounding the central portion of motor shaft 54. In this example the motor is a homopolar motor as described in my own U.S. Pat. No. 7,240,515 (which is hereby incorporated by reference). Magnet 106 is provided within the motor shaft. First stage impeller 42 is mounted on a first end of motor shaft 54 and second stage impeller 48 is mounted on a second end.

The motor shaft is preferably supported by axial bearings. Axial bearing 94 supports the end of the motor shaft that is proximate the first stage impeller. This bearing is attached to motor support 100. Axial bearing 122 supports the end of the motor shaft that is proximate the second stage impeller. Axial bearing 122 is connected to second stage labyrinth tube 120 (which in turn is supported by second stage labyrinth 116 and second stage diffuser support 110).

Foil bearing 102 is preferably provided as well. The foil bearing is supported by motor support 100. In addition, a small thrust bearing 96 is provided to counteract any residual force in a direction that is parallel to central axis 86. The tractive forces created by the first and second stage impellers largely cancel each other out. However, this cancellation is not perfect and thrust bearing 96 is provided to counteract any residual force.

The motor and bearings are part of a rigid assembly that is designed to be clamped together. Multiple though bolt assemblies 108—only one of which is visible in FIG. 11—connect motor support 100 to second stage diffuser support 110. These pass through the motor laminations of the motor stator as well. The through bolt assemblies are designed to properly locate the motor stator between motor mount 100 and second stage diffuser support 110.

The internal refrigerant flow through the components within the housing is complex. It begins with volute 67 receiving the discharge from first stage impeller 42. Motor support 100 and housing 98 both include a smooth radius proximate volute 67 that allows the refrigerant flow to bend around the corner to a direction that is roughly parallel to central axis 86. The flow then enters internal passage 68 between housing 98 and stator tube 104.

The internal passage created by stator tube 104 is not a simple annular space. FIG. 13 provides a perspective view of stator tube 104—looking at the inlet side of the component. The stator tube includes numerous guide vanes 134 and 136. Outer surface 138 on these guide vanes mates to the inward-facing surface on the interior of housing 98. The refrigerant flowing through internal passage 68 enters the gap between the stator tube and the housing on the left side of the view. The flow then proceeds between the guide vanes 134,136 as indicated by the arrows. The flow entering internal passage 68 has a high rotational component that it is imparted by the spinning of the first stage impeller. The guide vanes help to transition this flow to a parallel flow (parallel to the central axis of the compressor).

FIG. 14 shows stator tube 104 from the outlet side. Exit surface 146 of stator tube 104 mates to the entrance surface of the next component in line—second stage diffuser support 110 (see FIG. 11). The refrigerant flow passes out of the stator tube and into the next component at this point. Looking at FIG. 14, the reader will note that the refrigerant gas is able to flow past exit surface 146 through numerous flow gaps 147.

Before leaving the detailed description of the stator tube, another feature warrants explanation. Looking back at FIG. 13, the reader will note the presence of numerous cooling outlets 142. In this exemplary embodiment, some of the refrigerant flow is used to cool the motor. Cooling outlets 142 allow this refrigerant to return from the cavity surrounding the motor to the main interstage flow traveling through internal passage 68 on its way to the second stage impeller. In order to understand the route of the flow used to cool the motor, the reader's attention is directed back to the assembly of FIG. 11.

The embodiment shown is intended for use in an HVAC system that includes an economizer circuit. The return flow from the economizer enters the housing at economizer inlet 118. FIG. 12 shows a view of housing 98 by itself. The reader will note the presence of one or more economizer inlets 118 through the wall of the housing. Looking at FIG. 11, the reader will note how the economizer inlet 118 through the housing aligns with a radial passage through the stator tube. FIG. 13 labels these radial passages 144 in the stator tube 104. Returning now to FIG. 11, the reader will note how the economizer return flow travels through economizer inlet 118 (in the housing), through radial passage 144 (in the stator tube) and then to motor cavity 88. This refrigerant return flow then flows around and through the motor before leaving the motor cavity via cooling outlets 142 in stator tube 104.

The reader should note that many radial passages 144 through the stator tube may not be used. Looking again at FIG. 12, the reader will observe only a single economizer inlet 118 through housing 98. Other embodiments may include two or more economizer inlets through housing 98. Where these are provided, they will be aligned with radial passages 144 in the stator tube. It is also desirable to provide passages for power and control wiring. Actual working embodiments will therefore provide some additional passages through housing 98 in addition to the single economizer inlet 118 shown. Wiring or other components passing through these passages can use some of the additional radial passages 144 available in the stator tube.

Returning to FIG. 14, the reader will recall that the refrigerant flows over the stator tube (between the guide vanes and inside the encompassing housing 98) until it exits through flow gaps 147. The refrigerant next flows into second stage diffuser support 110. Exit surface 146 is the boundary between stator tube 104 and second stage diffuser support 110. FIG. 15 shows second stage diffuser support 110. Entrance surface 148 on second stage diffuser support 110 mates to exit surface 146 on stator tube 104.

Guide vanes 153 on second stage diffuser support 110 connect smoothly to guide vanes 134, 136 on stator tube 104. Thus, flow gaps 152 on second stage diffuser support 110 align with flow gaps 147 on stator tube 104. The outer perimeter surfaces on the guide vanes 153 seal against the inner cylindrical surface of housing 98—thereby confining the interstage flow to the flow gaps 152. The interstage flow through the second stager diffuser support is indicated in part by the arrows shown. The reader will also note that second stage diffuser support 110 includes four female-threaded mounting holes 150. These serve as attachment points for the four through bolt assemblies 108 that connect motor support 100, motor 55, and second stage diffuser support 110.

FIG. 16 shows the outlet side of second stage diffuser support 110. Exit surface 154 is a planar surface lying on the outlet side of guide vanes 153. The reader will note how the shape of guide vanes 153 directs some of the interstage flow inward as the flow approaches exit surface 154. Exit surface 154 in this instance is a plane where second stage diffuser support 110 mates to the next component in the outlet direction—intermediate connector 114.

FIG. 17 shows the inlet side of intermediate connector 114. Entrance surface 156 on intermediate connector 114 mates to exit surface 154 on second stage diffuser support. Flow gaps 158 at entrance surface 156 correspond to the shape of flow gaps 152 at exit surface 154 on second stager diffuser support 110. The interstage flow through the intermediate connector is indicated in part by the arrows shown.

FIG. 18 shows the outlet side of intermediate connector 114. The cross-sectional area of flow gaps 158 decrease as the flow gaps transition to exit surface 160. Exit surface 160 on intermediate connector 114 mates to the next component—second stage labyrinth 116.

The second stage labyrinth is a significant component in that it—in combination with other components—carries both the interstage flow and the second stage exit flow. FIG. 19 shows the inlet side of the second stage labyrinth. Entrance surface 162 of second stage labyrinth 116 mates to exit surface 160 of intermediate connector 114. The interstage flow travels through flow gaps 164—some of the interstage flow being indicated by arrows in the view.

FIG. 20 shows the outlet side of second stage labyrinth 116. The reader will note how the interstage flow passes through flow gaps 168—as indicated by the linear arrows. This side of second stage labyrinth also contains exit channels 170, which carry the discharge flow of the second stage impeller. In order to fully understand the nature of these exit channels 170, it is important to understand the cooperation between second stage labyrinth 116 and the next component encountered when traveling in the outlet direction—second stage inlet vane plate 124.

FIG. 21 shows the inlet side of second stage inlet vane plate 124. In viewing FIGS. 20 and 21 together, the reader should appreciate that entrance surface 173 on the second stage inlet vane plate 124 mates to exit surface 166 on second stage labyrinth 116. Further, outside radius fillet 183 on the outer perimeter of second stage inlet vane plate 124 mates to inside radius fillet 185 on second stage labyrinth 116. Entrance surface 173 thereby becomes the fourth side wall of each of the exit channels 170—meaning that each of the exit channels becomes a closed channel.

Looking again at FIG. 20, the reader will note that second stage labyrinth 116 includes second stage impeller recess 181. The base of the second stage impeller—the side closest to the motor shaft—rests in this impeller recess. FIG. 11 shows this interrelationship. The reader will note how second stage impeller 48 rests within the impeller recess in second stage labyrinth 116.

Returning now to FIG. 20, the reader will note how the compressed refrigerant exiting the second stage impeller is forced to travel outward through exit channels 170. The exit channels are closed by entrance surface 173 (FIG. 21) of second stage inlet vane plate 124 until the second stage exit flow reaches the outermost extent of exit channels 170. Multiple second stage exits 172 are located at the outermost extent of exit channels 170—around the perimeter of the second stage labyrinth. These exits 172 lie just outside the outermost perimeter of second stage inlet vane plate 124 (recall that outside radius fillet 183 mates to inside radius fillet 185—leaving the second stage exits 172 just outside the perimeter of the mating radii). Looking at FIG. 20, the reader will note that second stage exit flow 179 flows radially outward through exit channels 170, then bends 90 degrees toward the compressor's outlet in the region of second stage exits 172.

Components that further direct the flow leading into the second stage impeller and components that further direct the second stage exit flow leaving second stage exits 172 will be described subsequently. However—at the present point—it is significant for the reader to note and understand how the interstage flow (which shortly becomes the second stage inlet flow) and the second stage exit flow are segregated by the structure of the components shown in FIGS. 20 and 21. In FIG. 20, the interstage flow 175 passes through flow gaps 168 in the direction indicated by the arrows. The second stage exit flow 179 flows radially outward through exit channels 170 and then bends toward the compressor's outlet as it passes through second stage exits 172.

Before leaving FIG. 21, the reader should also note the presence and shape of second stage impeller housing 180 on the inlet side of second stage inlet vane plate 124. Looking again at the assembly view of FIG. 11, the reader will note how second stage inlet vane plate 124 forms part of the flow path leading into the second stage impeller—including part of the housing for the impeller itself.

FIG. 22 shows the outlet side of second stage inlet vane plate 124. Flow gaps 176 provide for the continued passage of interstage flow 175. As stated previously, second stage impeller housing 180 actually ducts the interstage flow into the second stage impeller. Intake interface 187 lies proximate the leading (nose portion) of the second stage impeller. It will therefore be apparent that interstage flow 175 as depicted in FIG. 22 must undergo an approximately 180-degree course reversal in order to pass through intake interface 187 and into the second stage impeller. The next two components in line (proceeding toward the compressor's outlet) provide the needed course reversal. In order to understand how, it is preferable to simultaneously consider and discuss FIGS. 22-25.

FIG. 23 shows the next component in line—second stage inlet vane 126. Entrance surface 182 of second stage inlet vane 126 mates to exit surface 178 of second stage inlet vane plate 124. Flow gaps 184 in second stage inlet vane 126 align with flow gaps 176 in second stage inlet vane plate 124. Looking at FIG. 23, interstage flow 175 flows into flow gaps 184.

FIG. 24 shows second stage inlet vane 126 from the opposite side (the outlet side). The curving arrows show how interstage flow 175 reverses course and becomes second stage inlet flow 177. Interstage flow 175 is forced through flow gaps 184 between adjacent guide vanes 191. Mating surface 186 on second stage inlet vane 126 (shown in FIG. 24) mates to mating surface 188 on outlet diffuser 128 (shown in FIG. 25). Mating surface 188—in combination with guide vanes 191 on second stage inlet vane 126 creates a closed flow channel that forces the course reversal for the interstage flow. Looking against at FIG. 24, the reader will realize that the channels in between guide vanes 191 are fully closed and that these closed channels force the interstage flow to follow the curved path depicted. The interstage flow becomes second stage inlet flow 177—flowing back toward the inlet side of the compressor and through intake interface 189.

Returning to FIG. 20, the reader will recall that the second stage inlet flow is further compressed by the second stage impeller, directed radially outward through exit channels 170, and emerges through second stage exits 172. Additional features are required to carry the second stage exit flow from second stage exits 172 to the compressor's outlet.

Still looking at FIG. 20, second stage exits 172 lie in the plane of exit surface 202. Turning now to FIG. 25—entrance surface 203 of outlet diffuser 128 mates to exit surface 202 on second stage labyrinth 116. Outlet diffuser 128 includes numerous guide vanes 204 on its outer surface. Flow gaps 190—between adjacent guide vanes—align with second stage exits 172 (on second stage labyrinth 116). Flow gaps 190 receive second stage exit flow 179.

Mating surface 192 on outlet diffuser 128 mates against mating surface 196 on diffuser housing 130 (shown in FIG. 27). The mating of these two surfaces creates a closed channel for second stage exit flow 179. FIG. 26 shows outlet diffuser 128 from the opposite side (outlet side). The reader will recall that the diffuser housing 130 closes the open side of channels 194 so that the second stage exit flow is forced through the closed channels—as indicated by the arrows. Guide vanes 202 gradually narrow to form thin vanes 132, which lie proximate the outlet 78 of the diffuser housing 130.

FIG. 27 shows diffuser housing 130 and the location of outlet 78. FIG. 28 shows the same component from the outlet side. Flange 198 is configured to mate to flange 101 on second stage labyrinth 116 (see assembly in FIG. 11). Still looking at FIG. 11, the reader will perceive how the assembly of housing 98, second stage labyrinth 116 and diffuser housing 130—the upstanding flanges providing a convenient assembly point in this example—creates an overall housing for the compressor. The reader will also note how the interstage flow is contained entirely within this overall housing.

A summary of the flow in, through, and out of the embodiment of FIG. 11 will now be provided. This summary is given in reference to the section assembly view of FIG. 11, though the reader may wish to refer to the detailed component view from time to time as well. It is not possible to provide a single sectional plane through the assembly that shows the entire flow path—since the flow path is curved and complex. For this reason, reference to the detailed component views is recommended.

In looking at FIG. 11, the reader will note that the compressor's components are generally aligned along central axis 86. Refrigerant enters the compressor through inlet 44. First stage impeller 42 compresses the refrigerant to an intermediate pressure and propels it out (in a radial direction) to outer volute 67. The flow between the first and second stage impellers is known as interstage flow. The interstage flow is propelled through a passage between the inlet side of motor support 100 and the inward facing side of housing 98. This passage bends through approximately 90 degrees so that the interstage flow bends around the outer perimeter of motor support 100 and assumes a direction that is approximately parallel to central axis 86.

The interstage flow next enters an annular passage—interstage passage 68—between housing 98 and stator tube 104. Guide vanes are provided as explained previously. These guide vanes assist in removing the rotational component of the flow exiting the first stage compressor and transitioning it to a more linear flow moving in the outlet direction. The reader will recall that stator tube 104 may include passages allowing some of the refrigerant flow to be diverted through motor cavity 88 for cooling purposes. In some examples the economizer return flow enters the motor cavity and the stator tube 104 includes passages allowing this economizer return flow to enter internal passage 68 and merge with the interstage flow.

The interstage flow next leaves the area of stator tube 104 and passes through flow gaps in second stage diffuser support 110 (The flow gaps are not clearly visible in FIG. 11 but may be easily seen in FIGS. 15 and 16). The interstage flow next passes through corresponding flow gaps in intermediate connector 114, second stage labyrinth 116, and second stage inlet vane plate 124 (These flow gaps are easily seen in FIGS. 17, 19, and 21).

The interstage flow then enters a curved passage between the outlet side of second stage inlet vane 126 and the inlet side of outlet diffuser 128. This passage urges the interstage flow through an approximately 180 degree change in direction. First the interstage flow is urged inward toward central axis 86 and then—continuing around the curved passage—the interstage flow is urged in the inlet direction toward the intake of second stage impeller 48.

Second stage impeller 48 further compresses the refrigerant flow and discharges it through radial exit channels 170 in second stage labyrinth 116 (FIG. 20 shows the exit channels). The assembly of second stage labyrinth 116 and second stage inlet vane plate 124 creates sealed exit channels for the second stage exit flow 179 and the interstage flow 175. These two refrigerant flows—interstage and exit—are thereby compelled to pass through the same vicinity while remaining segregated.

The second stage exit flow arrives in outer volute 206. Here it is turned in an approximately 90-degree bend to the outlet direction and forced into an annular passage between the outward side of outlet diffuser 128 and the inward side of diffuser housing 130. The second stage exit flow then moves through this passage—guided by vanes 132—until reaching outlet 78 and leaving the compressor.

The inventive compressor may be physically realized in an endless variety of embodiments. The inventive compressor may also be installed in an endless variety of applications. As it may benefit the reader's understanding, a brief discussion of two exemplary applications is provided. Returning first to FIG. 1, the reader will recall that the inventive two-stage compressor can be used in the role of compressors 12,14 in the HVAC system 10 of FIG. 1. This is a conventional HVAC system such as is commonly used in a large commercial building. The compressors are connected to the other components via pipes (though the compressors along with many other components shown in FIG. 1 may be unified in a single assembly such as a chiller).

FIG. 29 shows an elevation view of an embodiment of the inventive compressor 66—the same embodiment as depicted in a sectional view in FIG. 11. Low-pressure refrigerant is drawn in through inlet 44, compressed through the two stages within the compressor and expelled through outlet 78. Main housing 98 is attached indirectly to diffuser housing 130 across flange assembly 208. A second flange 210 is provided on the exterior of main housing 98. These two flanges are useful in attaching the compressor to other components. The reader will recall that one or more economizer inlets 118 provide a passage for the return flow of an economizer to enter the compressor 66 between the first and second stages. In this embodiment the economizer inlets are located between the two flanges.

FIG. 30 shows an exemplary installation of compressor 66 using external pipes. Evaporator-to-compressor line 214 is attached to inlet 44. This line connects the inlet 44 to the output of evaporator 34 in FIG. 1. Compressor-to-condenser line 216 is attached to outlet 78. This line connects the outlet 78 to the inlet of condenser 18. Economizer manifold 212 provides a hollow annular space that surrounds the exterior of main housing 98 between the two flanges 208, 210. Economizer-to-compressor line 218 feeds refrigerant from the economizer to economizer manifold 212. The gaseous refrigerant returning from the economizer (at an intermediate pressure) then enters the compressor through economizer inlets 118. The reader will thus perceive how the inventive compressor can be used as part of a conventional HVAC system.

The inventive compressor is also useful, however, as part of a wholly unconventional HVAC system. The inventive compressor can in fact be used as a component in a compact “microchiller”—such as seen in FIG. 8 of the commonly owned U.S. patent application Ser. No. 17/001,818 and as described in the text of the same patent. U.S. patent application Ser. No. 17/001,818 is hereby incorporated by reference.

FIG. 31 provides a schematic elevation view of micro chiller 220. Compressor 66 is an integral part of this micro chiller. As will be explained, the device depicted includes a compressor, a condenser, an economizer, an evaporator, and two heat exchangers used to exchange heat with an external heat sink or sinks. The view is deemed a “schematic” view because it uses very simple depictions to teach the fundamental concepts of such a device. In reality more complex structures would likely be used.

Housing 222 provides a sealed enclosure. Bulkheads 224 and 226 divide the interior of housing 222 into three separate, sealed compartments. Bulkhead 224 forms a tight seal with flange 210. Bulkhead assembly 226 forms a tight seal with flange assembly 208. Refrigerant can of course travel through the interior of compressor 66, but it cannot leak around the exterior of the compressor because of the gas-tight seals between the flanges and the bulkheads.

The left sealed compartment in the view of FIG. 31 comprises evaporator 34. The central sealed compartment comprises economizer 24. The right sealed compartment comprises condenser 18. Heat exchanger 228 is provided within evaporator 34. In this example, water is pumped through heat exchanger 228. This is called a cold water loop 232 because water passing through heat exchanger 228 is cooled by the operation of the micro chiller.

Heat exchanger 230 is provided within condenser 18. Water is pumped through heat exchanger 230. This is called hot water loop 234 because water passing through heat exchanger 230 is heated by the operation of the micro chiller.

The operation of micro chiller 220 will now be described by following a quantum of refrigerant around the refrigeration cycle carried on by the micro chiller. Gaseous, low-pressure refrigerant is pulled out of the upper portion of the enclosed volume serving as evaporator 34 (analogous to position “A” in FIG. 1) and into intake 44 of compressor 66. The refrigerant is compressed through both stages of the compressor and discharged as a high-pressure gas from outlet 78 (analogous to position “C” in FIG. 1).

The high-pressure refrigerant gas within condenser 18 transfers heat to the water circulating within heat exchanger 230, thereby condensing to a high-pressure liquid at the bottom of the enclosed volume serving as condenser 18. The high-pressure liquid travels out of condenser 18 through conduit 27 (analogous to position “D” in FIG. 1). A first branch off of conduit 27 leads to expansion valve 26. Expansion valves 26 allows refrigerant to flow into the intermediate-pressure volume of economizer 24. In the simplified depiction, conduit 27 is provided with attached plates that increase the surface area transferring heat between the intermediate-pressure refrigerant within economizer 24 and the high-pressure refrigerant within conduit 27, thereby enhancing the heat transfer rate between the refrigerant within the economizer and the refrigerant passing through conduit 27.

The remaining refrigerant passing through conduit 27 passes out of expansion valve 28 into evaporator 34 (returning to the low-pressure region). The refrigerant in evaporator 34 transfers heat to cold water loop 232 as it transitions to a gaseous state. The gaseous refrigerant is then pulled back into inlet 44 (corresponding to position “A” in FIG. 1) and the cycle repeats.

The simplified structure shown in FIG. 31 can be realized in a variety of ways. Heat exchangers 228, 230 can be made as a laminate of stamped (or molded or otherwise created) pieces that are brazed or glued together. In fact, the entire structure of the micro chiller can be made this way—stacking it together while simultaneously stacking together the components of compressor 66.

Thus, the reader will appreciate how the inventive compressor can be used in both conventional and unconventional HVAC systems. The inventive compressor has applications beyond the HVAC industry as well. The same general construction for the two-stage inventive compressor can be used to pump most any type of compressible or incompressible fluid. As a first additional example pertaining to a compressible fluid, the inventive compressor can be used to compress air. As an additional example pertaining to an incompressible fluid, the inventive compressor can be used as a two-stage water pump. Many other examples will occur to those skilled in the art. Thus, the term “compressor” as used in this disclosure should be understood to encompass anything that pressurizes a working fluid. The fluid may be many different substances including air, a pure gas, a refrigerant, or water.

The in-line configuration where the compressors inlet 44 and outlet 78 are aligned with the compressor's central axis is desirable in many applications. However, the in-line configuration may offer fewer advantages in others. Considering again the example of FIG. 31, the reader will note the that discharge of the second stage through a unified outlet 78 is not really needed, since there is no requirement to attach to a pipe—the compressed gas instead flowing out generally into the volume within condenser 18.

FIG. 32 shows still another embodiment. The configuration in this embodiment is generally similar to that shown in FIG. 5. Internal passage 68 carries the interstage flow to second stage transfer passage 70 and on to second stage inlet 72. However, in this embodiment, outlet transfer passages 236 lead radially outward from the outer volute of the second stage impeller housing. These second stage transfer passages then lead to multiple outlets 78—with the multiple outlet passages being radially arrayed around the centerline. Returning to the microchiller of FIG. 31, those skilled in the art will realize that multiple outlets 78—as depicted in the embodiment of FIG. 31—can evenly disperse the compressed refrigerant within condenser 18.

The reader will thereby perceive that the preferred embodiment of the invention can include and combine many advantageous features. A non-exhaustive listing of these features includes:

• • 1. An in-line configuration where the compressor's inlet and outlet lie on a common central axis;
  • 2. A configuration where the compressor's outlet is diffused about the perimeter of the compressor's housing.
  • 3. A single motor shaft that mounts a first stage impeller on a first end and a second stage impeller on a second end;
  • 4. The second stage impeller having a blade configuration that produces a tractive force in a direction opposing the tractive force created by the first stage impeller;
  • 5. The interstage flow between the first stage impeller and the second stage impeller traveling inside the compressor;
  • 6. The interstage flow passing in a direction that is parallel to the central axis, then undergoing an approximately 180-degree course reversal to enter the second stage compressor; and
  • 7. The interstage flow and the second stage exit flow passing through the same area while remaining segregated.

Of course, the invention is not limited to the preferred embodiments and will in fact include many other embodiments that will occur to those skilled in the art. Other potential features include:

• • 1. The first and second stage impellers each having multiple stages. As an example, the first stage impeller might include two separate impellers rotating in unison, with a small transfer passage in between;
  • 2. A version in which multiple shafts are provided along central axis 86, so that the second stage impeller can be rotated at a speed that is independent of the first stage impeller. Multiple motors can also be used;
  • 3. The housing can include multiple separate pieces that are joined together. As an example, the housing can include a central portion, another portion encompassing the first impeller, and still another portion encompassing the second impeller;
  • 4. The internal passage carries the interstage flow. It can include different sections, such as an annular internal passage 68 and a multitude of second stage transfer passages 70. On the other hand, the internal passage can be a single, unified passage that carries the interstage flow all the way to the second stage impeller inlet;
  • 5. The outlet transfer passage can likewise include multiple individual passages or it can be a single, unified passage that carries the second stage exit flow. The reader should bear in mind that the interstage flow and the second stage exit flow must pass by each other and must remain separate (as they exhibit significantly different pressures). If the internal passage is a single, unified passage then such an embodiment will need multiple outlet transfer passages passing through the internal passage. If the outlet transfer passage is a single, unified passage then such an embodiment will need multiple internal passages passing through the outlet transfer passage.

Although the preceding description contains significant detail, it should not be construed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. Thus, the scope of the invention should be fixed by the claims ultimately presented rather than the examples given.

Claims

1. A compressor for pressurizing a working fluid, comprising:

(a) a motor shaft having a first end, a second end, and a central axis;

(b) a motor driving said motor shaft;

(c) a first stage impeller attached to said first end of said motor shaft;

(d) a second stage impeller attached to said second end of said motor shaft;

(e) said second stage impeller in operation creating a second tractive force that opposes a first tractive force created by said first stage impeller;

(f) a housing containing said motor shaft, said first stage impeller, said second stage impeller, and said motor;

(g) said first stage impeller taking in said working fluid proximate said central axis and discharging an interstage flow;

(h) an internal passage carrying said interstage flow within said housing;

(i) said internal passage including a plurality of second stage transfer passages, with each of said second stage transfer passages receiving a portion of said interstage flow, bending said interstage flow through approximately 180 degrees, and directing said interstage flow into said second stage impeller;

(j) said second stage impeller taking in said interstage flow proximate said central axis and discharging a second stage exit flow;

(k) a plurality of outlet transfer passages, with each of said outlet transfer passages receiving a portion of said second stage exit flow and carrying it to an outlet; and

(l) said plurality of second stage transfer passages and said outlet transfer passages passing by each other in proximity to said second stage impeller, with said second stage transfer passages and said outlet transfer passages keeping said interstage flow separate from said second stage outlet flow.

2. The compressor for pressurizing a working fluid as recited in claim 1, wherein said outlet transfer passages join to form a single outlet.

3. The compressor for pressurizing a working fluid as recited in claim 2, wherein said single outlet lies proximate said central axis.

4. The compressor for a working fluid as recited in claim 1, wherein each of said outlet transfer passages flows to an individual outlet.

5. The compressor for a working fluid as recited in claim 4, wherein said individual outlets lie outward from said central axis.

6. The compressor for a working fluid as recited in claim 1, wherein a portion of said interstage flow is directed around said motor in order to cool said motor.

7. The compressor for a working fluid as recited in claim 1, further comprising an economizer inlet positioned to direct return flow from an economizer around said motor in order to cool said motor.

8. A compressor for pressurizing a working fluid, comprising:

(a) a motor shaft having a first end, a second end, and a central axis;

(b) a motor driving said motor shaft;

(c) a first stage impeller attached to said first end of said motor shaft;

(d) a second stage impeller attached to said second end of said motor shaft;

(e) said second stage impeller in operation creating a second tractive force that opposes a first tractive force created by said first stage impeller;

(f) a housing containing said motor shaft, said first stage impeller, said second stage impeller, and said motor;

(g) said first stage impeller taking in said working fluid proximate said central axis and discharging an interstage flow;

(h) an internal passage carrying said interstage flow within said housing;

(i) said internal passage bending said interstage flow through approximately 180 degrees, and directing said interstage flow into said second stage impeller;

(j) said second stage impeller taking in said interstage flow proximate said central axis and discharging a second stage exit flow;

(k) a plurality of outlet transfer passages, with each of said outlet transfer passages receiving a portion of said second stage exit flow and carrying it to an outlet; and

(l) said plurality of second stage transfer passages and said internal passage passing by each other in proximity to said second stage impeller, with said internal passage and said outlet transfer passages keeping said interstage flow separate from said second stage outlet flow.

9. The compressor for pressurizing a working fluid as recited in claim 8, wherein said outlet transfer passages join to form a single outlet.

10. The compressor for pressurizing a working fluid as recited in claim 9, wherein said single outlet lies proximate said central axis.

11. The compressor for a working fluid as recited in claim 8, wherein each of said outlet transfer passages flows to an individual outlet.

12. The compressor for a working fluid as recited in claim 8, wherein said individual outlets lie outward from said central axis.

13. The compressor for a working fluid as recited in claim 8, wherein a portion of said interstage flow is directed around said motor in order to cool said motor.

14. The compressor for a working fluid as recited in claim 8, further comprising an economizer inlet positioned to direct return flow from an economizer around said motor in order to cool said motor.

15. A compressor for pressurizing a working fluid, comprising:

(a) a motor shaft having a first end, a second end, and a central axis;

(b) a motor driving said motor shaft;

(c) a first stage impeller attached to said first end of said motor shaft;

(d) a second stage impeller attached to said second end of said motor shaft;

(e) said second stage impeller in operation creating a second tractive force that opposes a first tractive force created by said first stage impeller;

(f) a housing containing said motor shaft, said first stage impeller, said second stage impeller, and said motor;

(g) said first stage impeller taking in said working fluid proximate said central axis and discharging an interstage flow;

(h) an internal passage carrying said interstage flow within said housing;

(i) a plurality of second stage transfer passages, with each of said second stage transfer passages receiving a portion of said interstage flow, bending said interstage flow through approximately 180 degrees, and directing said interstage flow into said second stage impeller;

(j) said second stage impeller taking in said interstage flow proximate said central axis and discharging a second stage exit flow;

(k) an outlet transfer passage carrying said second stage exit flow to an outlet; and

(l) said plurality of second stage transfer passages and said outlet transfer passage passing by each other in proximity to said second stage impeller, with said second stage transfer passages and said outlet transfer passage keeping said interstage flow separate from said second stage outlet flow.

16. The compressor for pressurizing a working fluid as recited in claim 1, wherein said outlet transfer passage carries said second stage exit flow to a single outlet.

17. The compressor for pressurizing a working fluid as recited in claim 16, wherein said single outlet lies proximate said central axis.

18. The compressor for a working fluid as recited in claim 15, wherein a portion of said interstage flow is directed around said motor in order to cool said motor.

19. The compressor for a working fluid as recited in claim 16, wherein a portion of said interstage flow is directed around said motor in order to cool said motor.

20. The compressor for a working fluid as recited in claim 15, further comprising an economizer inlet positioned to direct return flow from an economizer around said motor in order to cool said motor.