System and method for unloading a multi-stage compressor

Abstract

Unloading a multi-stage compressor can include introducing a flow from a gas bypass from a condenser into a second stage inlet duct to induce a vortex in the fluid entering the second stage of compression. The unloading can be performed on a multi-stage compressor in a heating, ventilation, air conditioning, and refrigeration (HVACR) circuit that includes a gas bypass line from the condenser to a second stage inlet housing of the compressor. The multi-stage compressor can include an impeller inlet duct that includes a rectifier that receives a fluid flow from a first stage discharge, and one or more channels to introduce gas from the gas bypass into the fluid passing through the impeller inlet duct. The flow introduced by the channel can have a flow direction that includes a component opposite to the flow direction of the fluid flow discharged from the first stage through the rectifier.

Description

Technical Field

[0001] The present disclosure relates to unloading a multi-stage compressor, and in particular to introducing flow into the second stage of the compressor. Background Art

[0002] In a multi-stage compressor, the first stage of the compressor can be unloaded using guide vanes that control the mass flow entering the first stage suction inlet. When the first stage unloads without the second stage unloading accordingly, the second stage continues to draw flow, causing a drop in interstage pressure. The lower pressure at the second-stage impeller inlet reduces the mass flow enough to balance the flows. A common problem with many centrifugal compressor designs is that the unloading characteristics are not always stable. The reduction in flow and pressure can lead to instabilities in interstage flow and a phenomenon known as rotating stall or stall. This effect can be mistaken for surge, but in a stalled condition, there is no reverse flow through the compressor. Cyclic variations in mass flow and pressure occur, but the flow direction never reverses, as in a surge. The overall effect can range from unnoticeable to very objectionable noise and vibration. These effects can be particularly noticeable under high head conditions. Summary of the Invention

[0003] The present disclosure relates to unloading a multi-stage compressor, and in particular to introducing flow into the second stage of the compressor.

[0004] Introducing additional mass flow into the second-stage flow can stabilize a multi-stage compressor while the first stage is unloading. Furthermore, this mass introduction can be used to introduce swirl into the second-stage flow, thereby improving the efficiency of the second-stage unloading process. Furthermore, the introduction of mass flow can be used to adjust the velocity vector of the flow, controlling the head capacity and flow rate entering the compressor's second stage.

[0005] In one embodiment, a heating, ventilation, air conditioning, and refrigeration (HVACR) system includes a multi-stage compressor, a condenser, an expansion device, an evaporator, and a bypass line. The multi-stage compressor includes a first-stage discharge and a second-stage inlet that receives fluid from the first-stage discharge. The bypass line is a bypass line from the condenser to the second-stage inlet of the multi-stage compressor. The bypass line includes a valve. When the valve is open, the second-stage inlet receives a fluid flow. The second-stage inlet is configured to direct the fluid flow to merge with the fluid from the first-stage discharge, thereby forming a vortex in the combined fluid flow.

[0006] In one embodiment, the direction of the swirl is the same as the direction of rotation of the impeller in the multi-stage compressor.

[0007] In one embodiment, the second stage inlet is further configured to direct fluid flow in a direction having a component opposite to the direction of flow of the fluid from the first stage discharge. The component is a component of a vector of the fluid flow direction.

[0008] In one embodiment, the valve is a variable flow rate valve. In one embodiment, the valve is opened when the multi-stage compressor is unloaded.

[0009] In one embodiment, the second stage inlet does not include movable guide vanes.

[0010] In one embodiment, the multi-stage compressor further includes a first stage suction inlet and a plurality of movable guide vanes at the first stage suction inlet, wherein the plurality of movable guide vanes control mass flow into the multi-stage compressor.

[0011] In one embodiment, an inlet conduit for a multi-stage compressor includes an inlet configured to receive a first fluid flow from a first stage of the multi-stage compressor; and a plurality of channels configured to receive a second fluid flow from a bypass line and introduce the second fluid flow into the first fluid flow, thereby forming a vortex in the first fluid flow.

[0012] In one embodiment, the direction of the swirl is the same as the direction of rotation of the impeller in a multi-stage compressor.

[0013] In one embodiment, the channel is configured to introduce the second fluid flow into the first fluid in a direction having a component opposite to the direction of the first fluid flow.

[0014] In one embodiment, the channel is configured to introduce the second fluid flow into the first fluid in a direction having a component in the same direction as the direction of the first fluid flow.

[0015] In one embodiment, the passage is a through hole drilled from an outer surface of the inlet duct to an interior space of the inlet duct, and wherein the interior space of the inlet duct receives the first fluid flow from the first stage of the multi-stage compressor and through the inlet.

[0016] In one embodiment, a method for unloading a multi-stage compressor in a heating, ventilation, air conditioning, and refrigeration system includes receiving a first fluid stream from a first stage discharge of the multi-stage compressor at a second stage inlet of the multi-stage compressor; opening a bypass valve in a bypass line connecting a condenser to the second stage inlet, and directing a second fluid stream from the bypass line to merge with the first fluid stream through one or more channels in a conduit of the second stage inlet, such that the merged fluid stream has a vortex.

[0017] In one embodiment, the direction of the swirl is the same as the direction of rotation of the impeller in a multi-stage compressor.

[0018] In one embodiment, when the second fluid flow is directed to merge with the first fluid flow, the second fluid flow travels in a direction having a component opposite to the direction of the first fluid flow.

[0019] In one embodiment, when the second fluid flow is directed to merge with the first fluid flow, the second fluid flow travels in a direction having a component in the same direction as the direction of the first fluid flow.

[0020] In one embodiment, the method further includes reducing the flow velocity into the first stage of the multi-stage compressor using a plurality of movable guide vanes. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of a heating, ventilation, air conditioning, and refrigeration (HVACR) circuit according to one embodiment.

[0022] Figure 2 is a perspective view of an impeller duct according to one embodiment.

[0023] Figure 3 is a schematic diagram of an inlet housing according to one embodiment.

[0024] Figure 4 is a flow chart of a method of unloading a multi-stage compressor according to one embodiment.

[0025] Figure 5A is a graph of velocity vectors for first stage discharge flow and bypass flow within an impeller duct in a multi-stage compressor, according to one embodiment.

[0026] Figure 5B is a graph of velocity vectors from first stage discharge flow and bypass flow within an impeller duct in a multi-stage compressor according to another embodiment.

[0027] Figure 6 is a cross-sectional view of an assembled impeller duct and inlet casing according to one embodiment.

[0028] Figure 7 It is along Figure 6 Cross-sectional view taken along line AA. DETAILED DESCRIPTION

[0029] The present disclosure relates to unloading a multi-stage compressor, and more particularly, to directing flow into the second stage of the compressor.

[0030] Figure 1 is a schematic diagram of a heating, ventilation, air conditioning, and refrigeration (HVACR) circuit 100 according to one embodiment.

[0031] The HVACR circuit 100 includes a compressor 102 , a condenser 104 , an expansion device 106 , and an evaporator 108 .

[0032] The compressor 102, condenser 104, expansion device 106, and evaporator 108 may be fluidly connected to form an HVACR loop 100. The HVACR loop 100 may alternatively be configured to heat or cool a gaseous process fluid (e.g., a heat transfer medium or fluid such as, but not limited to, air), in which case the HVACR loop 100 may generally represent an air conditioner or heat pump.

[0033] The compressor 102 compresses a working fluid (e.g., a heat transfer fluid such as a refrigerant) from a relatively low-pressure gas to a higher-pressure gas. The relatively high-pressure gas is also at a higher temperature, and this gas is discharged from the compressor 102 and flows through the condenser 104. The compressor 102 is a multi-stage compressor. The compressor 102 includes a first-stage intake 110. The compressor 102 also includes a line 112 connecting the first stage to a second-stage intake 114. The line 112 can be, for example, a pipe. In the compressor 102, the working fluid is received at the first-stage intake 110, compressed for the first time, and then discharged from the first stage to the line 112. The working fluid compressed by the first stage is then received at the second-stage intake 114, compressed for a second time, and then discharged to the condenser 104.

[0034] The condenser 104 may be fluidly connected to a gas bypass line 116 . The gas bypass line 116 receives hot gas from within the condenser 104 and delivers the hot gas from the condenser 104 to the second stage inlet 114 of the compressor 102 .

[0035] Gas bypass line 116 may include a valve 118. Valve 118 regulates the flow of fluid through gas bypass line 116. In one embodiment, valve 118 is a valve having an open position and a closed position. In one embodiment, valve 118 is a variable flow rate valve, such as a valve having a plurality of discrete flow rates or a continuously variable flow rate. Valve 118 may be controlled based on unloading of the first stage of compressor 102, for example, increasing the flow through gas bypass line 116 when the first stage of compressor 102 is unloaded.

[0036] Passage 120 allows the fluid bypass flow from gas bypass line 116 to merge with the first stage discharge flow from line 112 in the second stage inlet 114 and enter the second stage of compressor 102. Passage 120 is oriented so that swirl is introduced into the combined flow of the first stage discharge flow from line 112 and the bypass flow from passage 120. In one embodiment, the direction of the swirl is the same as the direction of rotation of the rotating component within the second stage of compressor 102. In one embodiment, the combined flow can be a mass flow having a velocity less than the velocity of the first stage discharge flow when received from line 112. Example embodiments of passage 120 are described in detail in

[0028] Figure 2 is shown in and discussed below.

[0037] The HVACR circuit 100 also includes an expansion device 106. The expansion device 106 is a device configured to reduce the pressure of the working fluid. Thus, a portion of the working fluid is converted to a gaseous state. The expansion device 106 can be, for example, an expansion valve, an orifice, or other suitable expander to reduce the pressure of the refrigerant fluid (e.g., the working fluid).

[0038] Evaporator 108 is an evaporator in which the working fluid absorbs heat from the process fluid (e.g., water, glycol, air, etc.), heating the working fluid. This at least partially evaporates the working fluid. The working fluid then flows from evaporator 108 into the first-stage intake 110 of compressor 102. The circulation of the working fluid in HVACR circuit 100 continues while the refrigerant circuit is operating, for example, in cooling mode (e.g., upon starting compressor 102).

[0039] The HVACR system 100 can further include an economizer 122. The economizer 122 can introduce some of the working fluid from the condenser or near the condenser into the line 112 to deliver the fluid to the second stage inlet 114. The economizer 122 can be any standard economizer included in an HVACR circuit. In one embodiment, the economizer 122 includes a brazed plate heat exchanger.

[0040] Figure 2 FIG2 shows a perspective view of an impeller inlet duct 200 according to one embodiment. The impeller inlet duct 200 may be located at the inlet of the second stage of a multi-stage compressor, such as Figure 1 The second stage inlet 114 of the compressor 102 is shown. The impeller inlet duct includes a flow straightener 202, an interior space 204 defined by an outer wall 210, a plurality of passages 206, and an outlet 208.

[0041] The straightener 202 receives the fluid flow and is configured to smooth and straighten the received fluid flow. The straightener 202 may include a plurality of concentric circular openings connected by a plurality of blades to define a plurality of openings. The straightener 202 may guide the fluid flow entering the straightener 202 to the interior space 204 of the impeller inlet duct 200. The straightener 202 may be connected to a device such as Figure 1 The fluid line of line 112 shown and described above carries the discharge stream from the first stage of the multi-stage compressor to the rectifier 202. In one embodiment, the fluid line may further extend from Figure 1 An economizer such as economizer 122 shown and described above in FIG. 8 receives a fluid.

[0042] The interior space 204 is a hollow space within the impeller inlet duct 200. The interior space 204 may be defined by an outer wall 210 of the impeller inlet duct. The interior space 204 may receive fluid flows from the rectifier 202 and from the passage 206. The fluid flows from the rectifier 202 and from the passage 206 may merge and mix within the interior space 204. The interior space 204 may extend to an outlet 208, which allows the fluid to flow from the interior space 204 to the second stage of compression of the multi-stage compressor.

[0043] Channels 206 are one or more passages through which fluid flow can be introduced into interior space 204. In one embodiment, channels 206 are straight-through holes in outer wall 210 of impeller inlet duct 200. Non-limiting examples of channels 206 include holes, slots, or nozzles. Channels 206 can be arranged in one or more rows. The orientation of the channels is such that the fluid flow entering interior space 204 through channels 206 introduces vortexes into the fluid flow from rectifier 202 through interior space 204 to outlet 208. The number of channels can vary based on, for example, the size of channels 206 and the flow rate through channels 206, the orientation of the channels relative to interior space 204, and the characteristics of the compressor including impeller inlet duct 200. In one embodiment, channels 206 are oriented such that the flow direction L entering interior space 204 through channels 206 includes a tangential component to the direction F of the fluid flow from rectifier 202. This tangential component may induce vortexes in the combined flow in interior space 204.

[0044] In one embodiment, the passage 206 is further oriented such that the direction L of the flow entering the interior space 204 through the passage 206 includes a component in the opposite direction F of the fluid flow from the rectifier 202. As the fluid flows through the interior space 204, this velocity component reduces the velocity of the fluid flow in the direction F. Reducing the flow velocity (e.g., by reducing the volume of fluid entering the second stage of compression) can assist in unloading. In one embodiment, the passage is oriented such that the direction L of the fluid entering the interior space 204 through the passage 206 includes a component in the same direction as the direction F of the fluid flow from the rectifier 202. In this embodiment, the head can be increased by the component of the fluid flow through the passage 206 in the same direction as the direction F of the fluid flow in the passage 206.

[0045] The outlet 208 allows fluid from the interior space 204 , including fluid received at the rectifier 202 and fluid received via the passage 206 , to continue through the second stage of the compressor to be compressed.

[0046] Figure 3 FIG. 3 is a schematic diagram of an inlet housing 300 of a compressor according to one embodiment. The inlet housing 300 may surround an impeller inlet duct (e.g., Figure 2The impeller inlet duct 200 shown in FIG and described above) may include a second stage air inlet 302 and a bypass air inlet 308. The inlet housing 300 may be installed in a Figure 3 The direction of rotation R of the compressor is shown.

[0047] The second stage inlet hole 302 is a hole to which a fluid line discharged from the first stage of the multi-stage compressor can be connected. The fluid line can be, for example, Figure 1 The second stage inlet may provide a flow straightener between the fluid line from the first stage discharge and the inlet impeller conduit (e.g., as shown in FIG. Figure 2 The inlet impeller conduit 200 is in fluid communication with the rectifier 202 as shown and described above.

[0048] The bypass air inlet 308 may receive air from the condenser of the HVACR circuit (eg, Figure 1 3 and described above). Gas from the gas bypass can be delivered to a bypass inlet 308 via a gas bypass line 304. In one embodiment, the bypass gas can be supplied to the gas bypass line 304 from a compressor discharge source including the inlet housing 300. The flow through the gas bypass line 304 can be controlled by a valve 306. In one embodiment, the valve 306 is a valve having an open position and a closed position. In one embodiment, the valve 306 is a variable flow rate valve, such as a valve having multiple discrete flow rates or a continuously variable flow rate. The valve 306 can be controlled based on the unloading of the first stage of the compressor including the inlet housing 300, for example, when the first stage of the compressor is unloaded, the flow through the gas bypass line 304 is increased. In one embodiment, the valve 306 can be controlled in response to a measurement of a stall occurring in the compressor.

[0049] The fluid entering the inlet housing 300 through the bypass inlet 308 enters the space between the inlet housing and the impeller inlet duct of the compressor, for example Figure 2 The air inlet duct 200 shown in FIG and described above. This space can be separated from the path of the rectifier from the fluid line to the impeller air inlet duct provided by the second stage air inlet hole 302. The air flow can then continue through the channels, such as Figure 2 and Figure 6 The passages 206 and 614 shown then impart swirl to the airflow entering the second stage of the compressor through the second stage inlet opening 302 via an inlet duct (e.g., inlet duct 200). The direction of the swirl may be the same as the direction of rotation R of the rotating components of the second stage of the compressor.

[0050] Figure 44 is a flow chart of a method 400 for unloading a multi-stage compressor according to one embodiment. The method 400 optionally includes unloading a first stage 402 of the multi-stage compressor. The method 400 optionally includes receiving a first stage discharge flow 404, opening a bypass valve 406, directing the bypass flow to one or more passages 408, directing the bypass flow using the one or more passages 410, and combining the first stage discharge flow and the bypass flow to form a combined flow having a swirl 412.

[0051] Method 400 optionally includes unloading a first stage of a multi-stage compressor 402. At 402, unloading the first stage of the compressor may include regulating fluid flow into the first stage of the compressor using guide vanes, such as by deploying the guide vanes to restrict the fluid flow.

[0052] Method 400 includes receiving a first stage discharge stream at a second stage of a multi-stage compressor. The first stage discharge stream is a fluid stream that has been compressed by the first stage of the multi-stage compressor. In one embodiment, the first stage of the multi-stage compressor may be operated while unloading the first stage (e.g., by guide vanes at 402). In one embodiment, the first stage discharge stream may also include an economizer (e.g., Figure 1 In one embodiment, the rectifier at the impeller inlet pipe (e.g., at Figure 2 The first stage exhaust flow is received at the straightener 202 of the impeller inlet duct 200 as shown in FIG and described above. The straightener 202 can condition the first stage exhaust flow so that it flows smoothly through the inlet impeller duct in the same direction. The first stage exhaust flow is received at 404 and can continue to pass through the inlet impeller duct into the space within the inlet impeller duct, for example, as shown in FIG. Figure 2 and Figure 7 The interior spaces 204 and 700 are shown.

[0053] The method 400 also includes opening a bypass valve 406. At 406, the bypass valve is opened, which may be a valve such as Figure 1 The valve 118 shown in and described above or Figure 3 , and as described above. The valve can be along a bypass line, such as bypass line 116 or bypass line 304. Opening the bypass valve 406 allows fluid to flow through the bypass valve. In one embodiment, opening the bypass valve includes moving the bypass valve from a closed position to an open position. In one embodiment, opening the bypass valve includes increasing the flow of fluid through the bypass valve, wherein the bypass valve is a variable flow rate valve, such as a valve having multiple discrete flow rates or a continuously variable flow rate. In one embodiment, the degree to which the bypass valve is opened at 406 can be based on the degree of unloading of the multi-stage compressor, such as increasing the fluid flow in a greater amount when the unloading of the compressor is at a higher value, and / or when a compressor flow stall or instability is detected or determined to have occurred.

[0054] When the bypass valve is opened at 406, the bypass flow is directed from the bypass valve to one or more channels 408. The bypass flow can be directed to the one or more channels, for example, through a portion of the bypass line downstream of the bypass valve and / or through a housing surrounding the impeller inlet conduit that receives the bypass flow. The housing and the impeller inlet conduit can together provide a space between the housing and the impeller inlet conduit that allows fluid within the space to pass through the impeller conduit and into the channels (e.g., Figure 1 The above-mentioned channel 120 shown in Figure 2 and Figure 6 206 and channel 614) are shown in FIG.

[0055] At 410, the bypass flow is directed in one or more passages. At 410, the bypass flow is directed to the interior space of the impeller conduit at 404 (e.g., Figure 2 The first stage discharge flow received in the interior space 204 shown in FIG and described above. The fluid is directed through a channel formed in the impeller duct. The channel can direct the direction of the fluid entering the interior space of the impeller duct so that the fluid entering the impeller duct enters the interior space at a position and angle that causes a vortex when it merges with the first stage discharge flow received at 404. In one embodiment, the channel further directs the direction of the bypass flow into the interior space so that the fluid enters the interior space at a position and angle that causes a vortex when it merges with the first stage discharge flow received at 404. Figure 5A The spray angle I shown or Figure 5B The illustrated injection angle J introduces a bypass flow. In this embodiment, the vector representing the direction of the bypass flow includes a component in a direction opposite to the direction of the first stage discharge flow received at 404 .

[0056] At 410, the bypass flow directed by the one or more passages and the first-stage discharge flow received from the first stage of the compressor at 404 are combined to form a flow having swirl at 412. Due to the direction of the fluids directed by the one or more passages, the respective directions of each of the bypass and first-stage discharge flows result in a combined flow having swirl. In one embodiment, the direction of the swirl is the same as the direction of rotation of at least one rotating component of the second stage of compression of the multi-stage compressor. In one embodiment, the combined flow also has a linear velocity that is less than the linear velocity of the fluid received from the first stage of the compressor at 404. The combined flow can then enter the second stage of compression in the multi-stage compressor, where it is compressed and discharged from the multi-stage compressor.

[0057] Figure 5A FIG500 is a diagram of velocity vectors of fluid from first stage discharge and bypass flow within the impeller duct in a multi-stage compressor according to one embodiment. The velocity vectors represent the velocity vectors of the second stage impeller duct (e.g., Figure 2The velocity of the fluid flow within the impeller conduit 200 shown in and described above.

[0058] The first stage discharge flow velocity vector 502 represents the velocity of the fluid flow received from the first stage discharge of the multi-stage compressor. The first stage discharge flow is the flow received by the second stage at the impeller duct (e.g., impeller duct 200). The fluid provided by flowing through a rectifier (e.g., rectifier 202) can have a consistent direction. The fluid enters the impeller duct and travels in the direction from the first stage discharge toward the second stage compression in the multi-stage compressor.

[0059] A gas bypass flow is provided at an entry point 504. The entry point 504 is, for example, an opening at which a gas such as Figure 1 The passage 120 shown in FIG. 1 and the passage or passages 206 described above direct the fluid flow from the gas bypass into the fluid flow within the inlet conduit. The gas bypass flow has a velocity represented by the gas bypass flow velocity vector 506.

[0060] The gas bypass flow can be provided at an injection angle I relative to the first stage discharge flow velocity vector 502. In one embodiment, the injection angle I is 90 degrees. In one embodiment, the injection angle I is an acute angle. When the injection angle I is an acute angle, the component of the gas bypass flow velocity is opposite to the first stage discharge flow velocity, thereby reducing the overall velocity of the fluid flow entering the second stage of compression of the multi-stage compressor.

[0061] The total velocity of the combined first-stage discharge flow and gas bypass flow is represented by total velocity vector 508. Total velocity vector 508 includes swirl in one direction. In one embodiment, the direction of the swirl corresponds to the direction of rotation of components in the second stage of compression of the multi-stage compressor. In one embodiment, the velocity represented by total velocity vector 508 is reduced in speed compared to the first-stage discharge flow. The combined first-stage discharge flow and gas bypass flow travel into the second stage of compression of the multi-stage compressor at the velocity represented by total velocity vector 508.

[0062] Figure 5B FIG550 is a graph of velocity vectors of fluid from first stage discharge and bypass flow within the impeller duct in a multi-stage compressor according to one embodiment. The velocity vectors represent the velocity vectors of the second stage impeller duct (e.g., Figure 2 The velocity of the fluid flow within the impeller conduit 200 shown in and described above.

[0063] The first stage discharge flow velocity vector 552 represents the velocity of the fluid flow received from the first stage discharge of the multi-stage compressor. The first stage discharge flow is the flow received by the second stage at the impeller duct (e.g., impeller duct 200). The fluid provided by flowing through a rectifier (e.g., rectifier 202) can have a consistent direction. The fluid enters the impeller duct and travels in the direction from the first stage discharge toward the second stage compression in the multi-stage compressor.

[0064] A gas bypass flow is provided at entry point 554. Entry point 554 is, for example, an opening at which a channel (e.g. Figure 1 The passage 120 shown in FIG and described above (or passage 206 ) directs the fluid flow from the gas bypass to the fluid flow within the inlet conduit. The gas bypass flow has a velocity represented by the gas bypass flow velocity vector 556 .

[0065] The gas bypass flow may be provided at an injection angle J relative to the first stage exhaust flow velocity vector 552. Figure 5B In the illustrated embodiment, the injection angle J is an obtuse angle. When the injection angle J is an acute angle, the component of the gas bypass flow velocity is in the same direction as the first-stage discharge flow velocity, thereby increasing the overall velocity of the fluid flow entering the second stage of the multi-stage compressor. This can increase the head of the second stage of the compressor.

[0066] The total velocity of the combined first-stage discharge flow and gas bypass flow is represented by total velocity vector 558. Total velocity vector 558 includes swirl in one direction. In one embodiment, the direction of the swirl corresponds to the direction of rotation of the components in the second stage of compression of the multi-stage compressor. In one embodiment, the velocity represented by total velocity vector 558 is reduced in speed compared to the first-stage discharge flow. The combined first-stage discharge flow and gas bypass flow travel into the second stage of compression of the multi-stage compressor at the velocity represented by total velocity vector 558.

[0067] Figure 6 FIG2 is a cross-sectional view of an assembled impeller duct and inlet casing 600 according to one embodiment. The assembled impeller duct and inlet casing 600 receives a fluid flow from the first stage of a multi-stage compressor at a stage inlet 602 and directs the fluid flow to an impeller 616 and a second stage of the multi-stage compressor. The fluid flow is combined with a bypass flow received at a bypass inlet 608 and flowing into a space 610 defined by the inlet casing 606, where it enters a passage 614 in an impeller inlet duct body 612. The combined fluid flow and the bypass flow continue to an impeller 616.

[0068] The stage inlet 602 is defined by an inlet casing 606. The stage inlet 602 receives the fluid discharged from the previous stage of the compressor and directs it to the straightener 604 of the impeller inlet duct, which includes the assembled impeller duct and inlet casing 600. The straightener 604 may include a plurality of blades to regulate the flow of the fluid passing through it. The straightener 604 may be Figure 2 The rectifier 202 shown in FIG and described above. The fluid flowing through the rectifier 604 may enter the interior space defined by the impeller inlet duct body 612. Figure 7 The interior space 700 can be seen in the cross-sectional view provided in FIG.

[0069] The inlet housing 606 also includes a body that forms a space 610 between the inside of the inlet housing 606 and the impeller inlet duct body 612. The inlet housing 606 may be Figure 3 The inlet housing 300 shown in FIG and described above. The inlet housing 606 includes a bypass inlet 608 that allows fluid from the bypass line to be introduced into the space 610 within the inlet housing 606. In one embodiment, the bypass inlet 608 is fed from the bypass line (e.g., Figure 1 In one embodiment, the bypass inlet 608 receives fluid from a bypass line connected to the compressor discharge line. In one embodiment, the fluid received at the bypass inlet 608 can be controlled by a valve (e.g., the valves described above, respectively at Figure 1 and Figure 3 In one embodiment, the valves may be controlled based on unloading of the compressor and / or instability or stall detected or determined in the compressor.

[0070] The passage 614 may allow fluid to flow from the space 610 into the impeller inlet duct body 612. A bypass flow may enter the impeller inlet duct body 612 to join the fluid from the first stage of the multi-stage compressor that has passed through the rectifier 604. The passage 614 may be oriented to induce swirl in the combined fluid flow as it continues through the multi-stage compressor including the assembled impeller duct and inlet casing 600. The orientation of the interior space 700 within the impeller inlet duct body 612 and the passage 614 is Figure 7 shown in and described below.

[0071] The combined fluid flow from the first stage and the bypass then flows from within the impeller inlet duct body 612 to the impeller 616 and continues through the multi-stage compressor including the assembled impeller duct and inlet casing 600 .

[0072] Figure 7 It is along Figure 6 The sectional view taken along line AA in the figure. Figure 7In the cross-sectional view of FIG, the interior space 700 is visible, defined by the impeller inlet duct body 612. The interior space 700 receives fluid from the first stage discharge of the compressor through the rectifier 604. The direction of the passages 614 as they pass through the impeller inlet duct body 612 is visible. Arrow C shows the direction of rotation of the compressor receiving the fluid from the interior space 700. The passages 614 are oriented so that the velocity of the fluid flow introduced by those passages 614 has a component in a direction tangential to the flow direction of the fluid from the rectifier 604, which may flow into the compressor. Figure 7 The tangential component of the velocity of the fluid flow introduced by the passage 614 may induce vortexes in the combined fluid flow passing through the interior space 700. The vortexes induced in the combined flow passing through the interior space 700 may be in the same direction as the rotation direction C of the compressor receiving the combined fluid flow.

[0073] Implementation method:

[0074] It should be understood that any of Examples 1-9 may be combined with any of Examples 10-13 or 14-19, and any of Examples 10-13 may be combined with any of Examples 14-19.

[0075] Embodiment 1: A heating, ventilation, air conditioning, and refrigeration (HVACR) system, comprising:

[0076] a multi-stage compressor including a first stage discharge and a second stage inlet, the second stage inlet receiving fluid from the first stage discharge;

[0077] condenser;

[0078] expansion device;

[0079] evaporator; and

[0080] A bypass line from the condenser to the second stage inlet of a multi-stage compressor, the bypass line including a valve,

[0081] Wherein, when the valve is open, the second stage inlet receives a fluid flow, and the second stage inlet is configured to direct the fluid flow to merge with the fluid from the first stage discharge, thereby forming a vortex in the combined fluid flow.

[0082] Embodiment 2: The HVACR system according to embodiment 1, wherein the direction of the swirl flow is the same as the rotation direction of the impeller in the multi-stage compressor.

[0083] Embodiment 3. The HVACR system of any of embodiments 1-2, wherein the second stage inlet is further configured to direct the fluid flow in a direction having a component opposite to the flow direction of the fluid from the first stage discharge.

[0084] Embodiment 4. The HVACR system of any of embodiments 1-2, wherein the second stage inlet is further configured to direct the fluid flow in a direction having the same component as the flow direction of the fluid from the first stage discharge.

[0085] Embodiment 5. The HVACR system of any of embodiments 1-4, wherein the second stage inlet is further configured to direct the flow of the fluid in a direction having a component tangential to the flow direction of the fluid discharged from the first stage.

[0086] Example 6. The HVACR system of any one of examples 1-5, wherein the valve is a variable flow rate valve.

[0087] Embodiment 7. The HVACR system of any one of embodiments 1-6, wherein the valve is opened when the multi-stage compressor is unloaded.

[0088] Embodiment 8. The HVACR system of any one of embodiments 1 to 7, wherein the second stage inlet does not include movable guide vanes.

[0089] Embodiment 9. The HVACR system of any one of embodiments 1 to 7, wherein the multi-stage compressor further comprises a first-stage suction inlet and a plurality of movable guide vanes at the first-stage suction inlet, wherein the plurality of movable guide vanes control mass flow into the multi-stage compressor.

[0090] Embodiment 10. An inlet duct for a multi-stage compressor, comprising: an inlet configured to receive a first fluid flow from a first stage of the multi-stage compressor; and a plurality of channels configured to receive a second fluid flow from a bypass line and introduce the second fluid into the first fluid flow, thereby forming a vortex in the first fluid flow.

[0091] Embodiment 11. The inlet duct of claim 10, wherein the direction of the vortex is the same as the direction of rotation of the impeller in the multi-stage compressor.

[0092] Example 12. An inlet conduit according to any of Examples 10-11, wherein the channel is configured to introduce the second fluid flow into the first fluid in a direction having a component opposite to the direction of the first fluid flow.

[0093] Embodiment 13. An inlet duct according to any one of embodiments 10 to 12, wherein the passage is a through hole drilled from the outer surface of the inlet duct to the inner space of the inlet duct, and wherein the inner space of the inlet duct receives the first fluid flow entering from the first stage of the multi-stage compressor through the air inlet.

[0094] Example 14: A method for unloading a multi-stage compressor in a heating, ventilation, air conditioning, and refrigeration system, comprising:

[0095] receiving a first fluid stream from a first stage discharge of the multi-stage compressor at a second stage inlet of the multi-stage compressor;

[0096] opening a bypass valve in a bypass line connecting the condenser to the second stage inlet; and

[0097] A second fluid flow from the bypass line is directed through one or more passages in the conduit of the second stage inlet to merge with the first fluid flow such that the combined fluid flow has a swirl.

[0098] Embodiment 15. The method of claim 14, wherein the direction of the vortex is the same as the direction of rotation of the impeller in the multi-stage compressor.

[0099] Embodiment 16. The method of any of embodiments 14-15, wherein when the second fluid flow is directed to join the first fluid flow, the second fluid flow travels in a direction having a component opposite to the direction of the first fluid flow.

[0100] Embodiment 17. The method of any one of embodiments 14 to 15, wherein when the second fluid flow is directed to join the first fluid flow, the second fluid flow travels in a direction having the same component as the direction of the first fluid flow.

[0101] Embodiment 18. The method of any one of embodiments 14 to 17, wherein when the second fluid flow is directed to merge with the first fluid flow, the second fluid flow travels in a direction having a component tangential to the direction of the first fluid flow.

[0102] Embodiment 19. The method of any one of embodiments 14 to 18, further comprising using a plurality of movable guide vanes to reduce flow into the first stage of the multi-stage compressor.

[0103] In all embodiments, the examples disclosed in this application should be considered as illustrative rather than restrictive. The scope of the invention is indicated by the appended claims rather than the preceding description; and all changes within the meaning and equivalent range of the claims are included therein.

Claims

1. A heating, ventilation, air conditioning and refrigeration (HVACR) system, characterized in that: include: a multi-stage compressor comprising a first stage discharge and a second stage inlet, the second stage inlet receiving fluid from the first stage discharge; condenser; expansion device; evaporator; as well as a bypass line configured to deliver fluid directly from the condenser to the second stage inlet of the multi-stage compressor, the bypass line comprising a valve, wherein the second stage inlet receives a fluid flow when the valve is open, and the second stage inlet is configured to direct the fluid flow to join the fluid from the first stage discharge in a direction having a component having the same direction as the direction of flow of the fluid from the first stage discharge, and As the fluid flow joins the fluid discharged from the first stage, the head in the combined fluid flow increases before entering the second stage of compression.

2. The HVACR system according to claim 1, wherein: The second stage inlet is further configured to direct the fluid flow in a direction having a component tangential to the direction of flow of the fluid from the first stage discharge.

3. The HVACR system according to claim 1, wherein: The valve is a variable flow rate valve.

4. The HVACR system according to claim 1, wherein: When the multi-stage compressor is unloaded, the valve is opened.

5. The HVACR system according to claim 1, wherein: The second stage inlet does not include movable guide vanes.

6. The HVACR system according to claim 1, wherein: The multi-stage compressor further includes a first stage suction inlet and a plurality of movable guide vanes at the first stage suction inlet, wherein the plurality of movable guide vanes control a mass flow rate into the multi-stage compressor.

7. The HVACR system according to claim 1, wherein: The second stage inlet is further configured to direct the fluid flow to merge with fluid from the first stage discharge, thereby forming a vortex in the combined fluid flow.

8. An inlet duct for a multi-stage compressor of an HVACR system according to any one of claims 1 to 7, characterized in that: include: a rectifier configured to receive fluid discharged from a first stage of the multi-stage compressor; an outer wall defining an interior space, the outer wall extending from the rectifier to an outlet; and a plurality of channels distributed around the outer wall, each channel extending through the outer wall to the interior space, the plurality of channels being configured to receive a fluid flow from the bypass line and introduce the fluid flow into the fluid discharged from the first stage in a direction having a component, the component having a direction identical to a flow direction of the fluid discharged from the first stage, and such that when the fluid flow is introduced into the fluid discharged from the first stage, a head in the combined fluid flow is increased, wherein the outlet is configured to provide the combined fluid flow to the second stage of the multi-stage compressor.

9. The inlet pipe according to claim 8, characterized in that The passage is a through hole drilled from an outer surface of the inlet duct to an inner space of the inlet duct, and wherein the inner space of the inlet duct receives fluid discharged from a first stage of the multi-stage compressor through the rectifier.

10. The inlet pipe according to claim 8, characterized in that The plurality of channels are configured to create a vortex in the fluid discharged from the first stage.

11. A method for unloading a multi-stage compressor in a heating, ventilation, air conditioning and refrigeration system, characterized in that: include: receiving, at a second stage inlet of the multi-stage compressor, a first fluid stream discharged from a first stage of the multi-stage compressor at a rectifier of an inlet conduit; opening a bypass valve in a bypass line connecting the condenser directly to the second stage inlet; as well as A second fluid flow from the bypass line is directed to merge with the first fluid flow in the inlet conduit, the second fluid flow being in a direction having a component in the same direction as the direction of the first fluid flow when the second fluid flow is directed to merge with the first fluid flow, and the head of the combined fluid flow is increased when the second fluid flow merges with the first fluid flow.

12. The method according to claim 11, characterized in that When the second fluid flow is directed to merge with the first fluid flow, the second fluid flow travels in a direction having a component tangential to the direction of the first fluid flow.

13. The method according to claim 11 or 12, characterized in that Also included is using a plurality of movable guide vanes to reduce the flow velocity into the first stage of the multi-stage compressor.

14. The method according to claim 11 or 12, characterized in that When the second fluid flow merges with the first fluid flow, a vortex is induced in the combined fluid flow.

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