Centrifugal compressor

A centrifugal compressor includes: an impeller having full blades and splitter blades; a shroud wall forming an intake and having a shape conforming to the impeller; and a bleed chamber facing an outer surface of the shroud wall. The bleed chamber communicates with a discharge space having a pressure equal to or lower than a pressure of a working fluid at the intake. The shroud wall is provided with a slit (a bleeding passage) that directs a portion of the working fluid that has flowed into a space between the fullblade and a pressurizing surface of the splitter blade to the bleed chamber.

TECHNICAL FIELD

The present invention relates to a centrifugal compressor.

BACKGROUND ART

Conventionally, a centrifugal compressor configured to return a portion of a working fluid that passes through an impeller to an intake is known. For example, Patent Literature 1 discloses a centrifugal compressor100as shown inFIG. 7.

In this centrifugal compressor100, a cylindrical treatment chamber130is provided in a shroud wall120surrounding an impeller110. A slit-like first flow path131opens towards the impeller110at one end of the treatment chamber130, and a slit-like second flow path132opens into an intake101at the other end of the treatment chamber130.

CITATION LIST

Patent Literature

Patent Literature 1: JP 4100030 B

SUMMARY OF INVENTION

Technical Problem

Even if the configuration as described above is employed in a centrifugal compressor, there is still a lot of room for improvement in the performance of the compressor.

In view of this, it is an object of the present invention to enhance the performance of a centrifugal compressor.

Solution to Problem

The present disclosure provides a centrifugal compressor that compresses a working fluid, including: an impeller having alternately arranged full blades and splitter blades, the splitter blades being shorter than the full blades; a shroud wall forming an intake and having a shape conforming to the impeller; and a bleed chamber that communicates with a discharge space having a pressure equal to or lower than a pressure of the working fluid at the intake, the bleed chamber facing an outer surface of the shroud wall, wherein the shroud wall is provided with a bleeding passage that directs a portion of the working fluid that has flowed into a space between the full blade and a pressurizing surface of the splitter blade to the bleed chamber, and in a meridional projection obtained by rotationally projecting the full blade, the splitter blade, and the shroud wall on a meridian plane passing through a rotational axis of the impeller, a point of intersection of an upstream edge of the splitter blade and an outward edge of the splitter blade is located at a position closer to the intake than an intake-side edge of an opening of an inlet of the bleeding passage.

Advantageous Effects of Invention

According to the present disclosure, it is possible to enhance the performance of the centrifugal compressor.

DESCRIPTION OF EMBODIMENTS

First, the focus of the present disclosure is described.

An impeller of a centrifugal compressor typically has a configuration in which full blades and splitter blades shorter than the full blades are alternately arranged. A working fluid drawn into the centrifugal compressor first flows into the space between the full blades and then the flow of the fluid is split by the splitter blades. The gap between the outward edges of these blades and the shroud wall is often set to less than 10% of the height of the blades. However, in a small-sized centrifugal compressor, the gap between the outward edges of the blades and the shroud wall may be relatively large. In such a configuration, since the working fluid leaks through the gap between the outward edges of the blades and the shroud wall (in other words, the working fluid flows over the outward edges of the blades), vortices develop not only in the working fluid that has flowed into the space between the full blades but also in the working fluid that has flowed into the space between the full blade and the splitter blade. The present inventors have found that it is possible to prevent or suppress the above-described two-step development of vortices by bleeding both a portion of the working fluid that has flowed into the space between the full blades and a portion of the working fluid that has flowed into the space between the full blade and the splitter blade. Thereby, the performance of the centrifugal compressor can be enhanced.

It is possible to prevent or suppress the above-described development of vortexes even if only a portion of the working fluid that has flowed into the space between the full blade and the splitter blade. It is also possible to prevent or suppress the above-described development of vortexes even if only a portion of the working fluid that has flowed into the space between the full blades. The technique disclosed in this description has been made from this point of view.

The first aspect of the present disclosure provides a centrifugal compressor that compresses a working fluid, including: an impeller having alternately arranged full blades and splitter blades, the splitter blades being shorter than the full blades; a shroud wall forming an intake and having a shape conforming to the impeller; and a bleed chamber that communicates with a discharge space having a pressure equal to or lower than a pressure of the working fluid at the intake, the bleed chamber facing an outer surface of the shroud wall, wherein the shroud wall is provided with a bleeding passage that directs a portion of the working fluid that has flowed into a space between the full blade and a pressurizing surface of the splitter blade to the bleed chamber, and in a meridional projection obtained by rotationally projecting the full blade, the splitter blade, and the shroud wall on a meridian plane passing through a rotational axis of the impeller, a point of intersection of an upstream edge of the splitter blade and an outward edge of the splitter blade is located at a position closer to the intake than an intake-side edge of an opening of an inlet of the bleeding passage.

According to the first aspect, it is possible to bleed a portion of the working fluid that has flowed into the space between the full blade and the pressurizing surface of the splitter blade through the bleeding passage so as to prevent or suppress the development of vortices caused by the leakage of the working fluid through the gap between the outward edge of the splitter blade and the shroud wall. Thereby, the performance of the centrifugal compressor can be enhanced. In the case where the inlet of the bleeding passage is located at the position as described above, the portion of the working fluid that has flowed into the space between the full blade and the pressurizing surface of the splitter blade can be directed to the bleed chamber efficiently.

In the vicinity of the upstream edge of the full blade, there is no large difference between the pressure of the working fluid on the pressurizing surface of the full blade and the pressure of the working fluid on the non-pressurizing surface of the full blade. On the other hand, by the time the working fluid reaches the splitter blade, a relatively large difference is made between the pressure of the working fluid on the pressurizing surface of the full blade and the pressure of the working fluid on the non-pressurizing surface of the full blade. Therefore, the phenomenon in which the working fluid flows over the outward edges of the blades is more likely to occur in the splitter blades than in the full blades. In view of this, the performance of the centrifugal compressor can be enhanced effectively by forming the bleeding passage (slit) so as to direct the portion of the working fluid that has flowed into the space between the full blade and the pressurizing surface of the splitter blade to the bleed chamber.

A second aspect provides the centrifugal compressor as set forth in the first aspect, wherein the shroud wall is further provided with an additional bleeding passage that directs a portion of the working fluid that has flowed into a space between the adjacent full blades to the bleed chamber, and in the meridional projection, a point of intersection of an upstream edge of the full blade and an outward edge of the full blade is located at a position closer to the intake than an intake-side edge of an opening of an inlet of the additional bleeding passage. In the case where the inlet of the additional bleeding passage is located at the position as described above, the portion of the working fluid that has flowed into the space between the full blades can be directed to the bleed chamber efficiently.

A third aspect provides the centrifugal compressor as set forth in the second aspect, wherein a length of the additional bleeding passage in a circumferential direction of the shroud wall is shorter than a distance between the adjacent full blades at a position where the additional bleeding passage opens toward the impeller. This configuration makes it possible to avoid the simultaneous presence of the outward edges of two full blades over one additional bleeding passage and thus to cause each of the full blades to sweep the working fluid smoothly into the additional bleeding passage.

A fourth aspect provides the centrifugal compressor as set forth in the second or the third aspect, wherein in the meridional projection, the inlet of the additional bleeding passage is located at a distance ranging from 0.02 L1 to 0.4 L1 from the upstream edge of the full blade when a projected length of the outward edge of the full blade is defined as L1. In the case where the inlet of the additional bleeding passage is located at the position in this range, it is possible to prevent or suppress the development of vortices very effectively.

A fifth aspect provides the centrifugal compressor as set forth in any one of the second to fourth aspects, wherein the shroud wall is provided with a plurality of the bleeding passages and a plurality of the additional bleeding passages, and the bleeding passages and the additional bleeding passages are alternately arranged in a staggered manner in a circumferential direction of the shroud wall. This configuration makes it possible to efficiently bleed both the portion of the working fluid that has flowed into the space between the full blades and the portion of the working fluid that has flowed into the space between the full blade and the splitter blade.

A sixth aspect provides the centrifugal compressor as set forth in any one of the second to fifth aspects, wherein the number of the additional bleeding passages is equal to that of the full blades, and the additional bleeding passages are arranged at the same angular pitch as the full blades. This configuration makes it possible to avoid the simultaneous presence of the outward edges of two full blades over one additional bleeding passage and thus to cause each of the full blades to sweep the working fluid smoothly into the additional bleeding passage.

A seventh aspect provides the centrifugal compressor as set forth in any one of the first to sixth aspects, wherein a length of the bleeding passage in a circumferential direction of the shroud wall is shorter than a distance between the full blade and the splitter blade at a position where the bleeding passage opens toward the impeller. This configuration makes it possible to avoid the simultaneous presence of the outward edge of the full blade and the outward edge of the splitter blade over one bleeding passage and thus to cause the full blade and the splitter blade to sweep the working fluid smoothly into the bleeding passage.

A eighth aspect provides the centrifugal compressor as set forth in any one of the first to seventh aspects, wherein in the meridional projection, the inlet of the bleeding passage is located at a distance ranging from 0.02 L2 to 0.4 L2 from the upstream edge of the splitter blade when a projected length of the outward edge of the splitter blade is defined as L2. In the case where the inlet of the bleeding passage is located at the position in this range, it is possible to prevent or suppress the development of vortices very effectively.

A ninth aspect provides a refrigeration cycle apparatus including: a main circuit including an evaporator that retains a refrigerant liquid and evaporates the refrigerant liquid therein, a first compressor that compresses a refrigerant vapor, and a condenser that condenses the refrigerant vapor therein and retains the refrigerant liquid, wherein the evaporator, the first compressor, and the condenser are connected in this order; a first circulation path that allows the refrigerant liquid retained in the evaporator or a heat medium cooled in the evaporator to circulate via a heat exchanger for heat absorption; and a second circulation path that allows the refrigerant liquid retained in the condenser or a heat medium heated in the condenser to circulate via a heat exchanger for heat release, wherein the first compressor is the centrifugal compressor according to any one of the first to eighth aspects, and the refrigeration cycle apparatus further includes a return path that returns the refrigerant vapor from the bleed chamber of the centrifugal compressor to the evaporator.

According to the ninth aspect, the refrigerant vapor is returned from the bleed chamber of the centrifugal compressor to the evaporator through the return path. Thereby, the performance of the centrifugal compressor can be enhanced, and as a result, the performance of the refrigeration cycle apparatus can be enhanced.

A tenth aspect provides the refrigeration cycle apparatus as set forth in the ninth aspect, wherein the second compressor is a centrifugal compressor, and the first compressor and the second compressor are coupled together by a rotary shaft. The number of components of the first compressor and the second compressor can be reduced by coupling them together by the rotary shaft.

An eleventh aspect provides the refrigeration cycle apparatus as set forth in the ninth or the tenth aspect, wherein the return path is provided with a flow rate regulating valve. The efficiency of the centrifugal compressor can be optimized by regulating the flow rate of the refrigerant vapor by the flow rate regulating valve.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments.

Embodiments

FIG. 1andFIG. 2show a centrifugal compressor1A according to an embodiment of the present invention. The centrifugal compressor1A is coupled to an electric motor or to a turbine and a generator via a rotary shaft11. The centrifugal compressor1A is driven by the rotation of the rotary shaft11and compresses a working fluid.

Specifically, the centrifugal compressor1A includes an impeller2fixed to the rotary shaft11, a back plate13disposed behind the impeller2, and a housing15in which the impeller2is mounted. Hereinafter, for convenience of description, being directed to or being located on the front surface side of the back plate13and the back surface side thereof along the axial direction of the rotary shaft11may be referred to as “forward or ahead of” and “backward or behind”, respectively.

The impeller2includes: a main body20whose diameter gradually increases from the smallest diameter portion to the largest diameter portion along the axial direction of the rotary shaft11; and full blades21and splitter blades22extending from the flared outer peripheral surface of the main body20. The full blades21and the splitter blades22are arranged alternately in the circumferential direction of the impeller2. The splitter blade22is shorter than the full blade21, and as shown inFIG. 3, the downstream edge22cof the splitter blade22is located at the same position as the downstream edge21cof the full blade21, while the upstream edge22aof the splitter blade22is located behind the upstream edge21aof the full blade21. In each of the full blades21and the splitter blades22, the surface facing in the rotational direction of the impeller2is a pressurizing surface, and the surface opposite to the pressurizing surface is a non-pressurizing surface.

The housing15includes: a shroud wall3having a shape conforming to the impeller2; a flange5extending radially outwardly from the front end of the shroud wall3; a peripheral member17connected to the rear end of the shroud wall3; and a front member18interposed between the peripheral member17and the flange5. The shroud wall3extends forward beyond the impeller2so as to form an intake12, and the peripheral member17forms a volute chamber16around the impeller2. The volute chamber16communicates with a diffuser formed between the back plate13and the shroud wall3. In the present embodiment, the shroud wall3is divided into a front part and a rear part near the upstream edge21aof the full blade21of the impeller2, the front part of the shroud wall3and the flange5are integrated into a single unit, and the rear part of the shroud wall3and the peripheral member17are integrated into a single unit.

FIG. 3is a meridional projection (rotational projection) obtained by rotationally projecting the full blade21, the splitter blade22, and the shroud wall3on a meridian plane passing through the rotational axis A of the impeller2. The shape represented in the meridional projection is referred to as a “meridional shape” in the field of turbomachinery. In this description, the outer peripheral edge of the full blade21facing the intake12is defined as the upstream edge21aof the full blade21. The outer peripheral edge of the full blade21facing the shroud wall3is defined as the outward edge21bof the full blade21. Likewise, the outer peripheral edge of the splitter blade22facing the intake12is defined as the upstream edge22aof the splitter blade22. The outer peripheral edge of the splitter blade22facing the shroud wall3is defined as the outward edge22bof the splitter blade22.

The front member18and the flange5cover the space facing the outer surface of the shroud wall3. That is, the shroud wall3, the flange5, and the front member18form an annular bleed chamber4around the intake12. The front member18has a tubular surface18aextending forward beyond the flange5. The tubular surface18aforms a ring-shaped space (corresponding to a discharge space of the present invention)18bfacing the front surface of the flange5and communicating with the intake12. Since the ring-shaped space18bis filled with the working fluid, the ring-shaped space18bhas the same pressure as that of the working fluid at the intake12. As used herein, “the same pressure” refers to a concept including not only a state in which the pressure of the ring-shaped space18bis exactly equal to the pressure of the working fluid at the intake12but also a state in which the pressure of the former is higher than the pressure of the latter by the loss of pressure.

The flange5is provided with an arcuate opening51, and the bleed chamber4communicates with the ring-shaped space18bthrough this opening51.

The shroud wall3is provided with a plurality of first slits31(additional bleeding passages) and a plurality of second slits32(bleeding passages) each extending in the circumferential direction. The first slit31opens into the bleed chamber4and the space near the upstream edge21aof the full blade21of the impeller2. The second slit32opens into the bleed chamber4and the space near the upstream edge22aof the splitter blade22. The first slits31and the second slits32are alternately arranged in a staggered manner in the circumferential direction. The first slits31and the second slits32need not necessarily be exactly parallel to the circumferential direction, and they may be slightly inclined from the circumferential direction.

The first slit31directs a portion of the working fluid that has flowed into the space between the adjacent full blades21to the bleed chamber4. The second slit32directs a portion of the working fluid that has flowed into the space between the full blade21and the pressurizing surface of the splitter blade22to the bleed chamber4. For example, the number of the first slits31is equal to the number of the full blades21, and the first slits31and the full blades21are arranged at the same angular pitch. This configuration makes it possible to avoid the simultaneous presence of the outward edges21bof two full blades21over one first slit31and thus to cause each of the full blades21to sweep the working fluid smoothly into the first slit31.

As shown inFIG. 3andFIG. 4, the first slit31opens at a position behind the upstream edge21aof the full blade21and ahead of the upstream edge22aof the splitter blade22in the axial direction of the rotary shaft11. Specifically, as shown inFIG. 4, in the meridional projection, a point of intersection21tof the upstream edge21aof the full blade21and the outward edge21bof the full blade21is located at a position closer to the intake12than the intake-side edge31eof the opening of the inlet of the first slit31. In the present embodiment, the entire inlet of the first slit31faces the outward edge21bof the full blade. In the case where the inlet of the first slit31is located at such a position, a portion of the working fluid that has flowed into the space between the full blades21can be directed to the bleed chamber4efficiently.

The second slit32opens at a position behind the upstream edge22aof the splitter blade22in the axial direction of the rotary shaft11. Specifically, as shown inFIG. 4, in the meridional projection, a point of intersection22tof the upstream edge22aof the splitter blade22and the outward edge22bof the splitter blade22is located at a position closer to the intake12than the intake-side edge32eof the opening of the inlet of the second slit32. In the present embodiment, the entire inlet of the second slit32faces the outward edge22bof the splitter blade22. In the case where the inlet of the second slit32is located at such a position, a portion of the working fluid that has flowed into the space between the full blade21and the pressurizing surface of the splitter blade22can be directed to the bleed chamber4efficiently.

It is desirable that the length of the first slit31in the circumferential direction of the shroud wall3be shorter than the distance between the adjacent full blades21at a position where the first slit31opens towards the impeller2. This is because this configuration makes it possible to avoid the simultaneous presence of the outward edges21bof two full blades21over one first slit31and thus to cause each of the full blades21to sweep the working fluid smoothly into the first slit31. From the same point of view, it is desirable that the length of the second slit32in the circumferential direction of the shroud wall3be shorter than the distance between the full blade21and the splitter blade22at a position where the second slit32opens towards the impeller2.

As shown inFIG. 3, on the meridian plane passing through the rotational axis A of the impeller2(the central axis of the rotary shaft11), the inlet of the first slit31(the opening on the impeller2side) is located at a distance ranging, for example, from 0.02 L1 to 0.4 L1 (or from 0.05 L1 to 0.1 L1) from the upstream edge21aof the full blade21, when the projected length of the outward edge21bof the full blade21is defined as L1. On the other hand, the inlet of the second slit32(the opening on the impeller2side) is located at a distance ranging, for example, from 0.02 L2 to 0.4 L2 (or from 0.05 L2 to 0.1 L2) from the upstream edge22aof the splitter blade22, when the projected length of the outward edge22bof the splitter blade22is defined as L2. The width of the first slit31is, for example, three to five times the thickness of the full blade21at a position where the full blade21faces the first slit31. Likewise, the width of the second slit32is, for example, three to five times the thickness of the splitter blade22at a position where the splitter blade22faces the second slit32. As used herein, the term “projected length” refers to the length of the arc formed by the outward edge21bor22bin the meridional projection inFIG. 3.

In the centrifugal compressor1A described above, it is possible to bleed a portion of the working fluid that has flowed into the space between the full blades21through the first slit31so as to prevent or suppress the development of vortices caused by the leakage of the working fluid through the gap between the outward edges21bof the full blades21and the shroud wall3. It is also possible to bleed a portion of the working fluid that has flowed into the space between the full blade22and the pressurizing surface of the splitter blade22through the second slit32so as to prevent or suppress the development of vortices caused by the leakage of the working fluid through the gap between the outward edges22bof the splitter blades22and the shroud wall3. Thereby, the performance of the centrifugal compressor1A can be enhanced.

Vortices caused by the leakage of the working fluid through the gap between the outward edges of the blades and the shroud wall are often formed immediately downstream of the upstream edges of the blades. For this reason, when the opening (inlet) of the first slit31is located at a distance ranging from, for example, 0.02 L1 to 0.4 L1 (or 0.05 L1 to 0.1 L1) from the upstream edge21aof the full blade21, it is possible to prevent or suppress the development of such vortices very effectively. Likewise, when the opening (inlet) of the second slit32is located at a distance ranging from, for example, 0.02 L2 to 0.4 L2 (or 0.05 L2 to 0.1 L2) from the upstream edge22aof the splitter blade22, it is possible to prevent or suppress the development of such vortices very effectively.

As shown inFIG. 5, a centrifugal compressors1B according to a modification has the same configuration as the centrifugal compressor1A described above with reference toFIGS. 1 to 4, except that the shroud wall3is not provided with the first slit31. The shroud wall3is provided with at least one second slit32as a bleeding passage that directs a portion of the working fluid to the bleed chamber4. The description of the centrifugal compressor1A is applicable to the other parts of the centrifugal compressor1B.

In the vicinity of the upstream edge21aof the full blade21, there is no large difference between the pressure of the working fluid on the pressurizing surface of the full blade21and the pressure of the working fluid on the non-pressurizing surface of the full blade21. On the other hand, by the time the working fluid reaches the splitter blade22, a relatively large difference is made between the pressure of the working fluid on the pressurizing surface of the full blade21and the pressure of the working fluid on the non-pressurizing surface of the full blade21. Therefore, the phenomenon in which the working fluid flows over the outward edges of the blades is more likely to occur in the splitter blades22than in the full blades21. In view of this, the performance of the centrifugal compressor1B can be enhanced effectively by forming the bleeding passage (slit32) so as to direct the portion of the working fluid that has flowed into the space between the full blade21and the pressurizing surface of the splitter blade22to the bleed chamber4.

In the above-described embodiment, a plurality of first slits31and a plurality of second slits32are provided. One first slit31and one second slit32may be provided.

The cross-sectional shape of the bleeding passage that directs the portion of the working fluid to the bleed chamber4is not particularly limited. For example, instead of the first slit31, a through-hole having another cross-sectional shape, such as a circle, an ellipse, or a rectangle, may be provided. The bleeding passages having different cross-sectional shapes from each other may be formed in the shroud wall3along the circumferential direction thereof. The same applies to the second slit32.

In the above-described embodiment, through the opening51provided in the flange5, the bleed chamber4communicates with the ring-shaped space18bcommunicating with the intake12. However, the bleed chamber4may communicate with a space having a pressure lower than the pressure of the working fluid at the intake12. For example, the bleed chamber4may communicate with a negative pressure source (for example, the intake side of another compressor) disposed separately from the centrifugal compressor1A or1B, through a flow path penetrating the housing15.

The applications of the above-described centrifugal compressors1A and1B are not particularly limited. They may be used in stationary gas turbine generators, or gas turbine generators to be mounted in vehicles such as automobiles. Instead, the centrifugal compressors1A and1B can be used in, for example, a refrigeration cycle apparatus10as shown inFIG. 6.

The refrigeration cycle apparatus10includes: a main circuit6that allows a refrigerant to circulate; a first circulation path7for heat absorption; and a second circulation path8for heat release. The main circuit6, the first circulation path7, and the second circulation path8are filled with a refrigerant in the form of liquid at ordinary temperature. More specifically, a refrigerant whose saturated vapor pressure is a negative pressure at ordinary temperature is used as the refrigerant. Examples of such a refrigerant include refrigerants whose main component is water or alcohol. The pressure in each of the main circuit6, the first circulation path7, and the second circulation path8is a negative pressure lower than the atmospheric pressure. In this description, the term “main component” refers to a component whose content is the highest in mass ratio.

The main circuit6includes an evaporator66, a first compressor61, an intercooler62, a second compressor63, a condenser64, and an expansion valve65, and these devices are connected in this order by flow paths.

The evaporator66retains a refrigerant liquid, and evaporates the refrigerant liquid therein. Specifically, the refrigerant liquid retained in the evaporator66is circulated via a heat exchanger for heat absorption71through the first circulation path7. For example, in the case where the refrigeration cycle apparatus10is an air conditioner for cooling an indoor space, the heat exchanger for heat absorption71is placed in the indoor space, and cools the indoor air supplied by an air blower through heat exchange with the refrigerant liquid.

The refrigerant vapor is compressed in two stages by the first compressor61and the second compressor63. The above-described centrifugal compressor1A or1B is used as the first compressor61. The second compressor63may be a positive displacement compressor independent of the first compressor61. However, in the present embodiment, the second compressor63is a centrifugal compressor coupled with the first compressor61by a rotary shaft11. An electric motor67that rotates the rotary shaft11may be disposed between the first compressor61and the second compressor63, or may be disposed outside one of these compressors. The number of components of the first compressor61and the second compressor63can be reduced by coupling them together by the rotary shaft11.

The intercooler62cools the refrigerant vapor discharged from the first compressor21before the refrigerant vapor is drawn into the second compressor22. The intercooler62may be a direct contact heat exchanger, or an indirect heat exchanger.

The condenser64condenses the refrigerant vapor therein, and retains the refrigerant liquid. Specifically, the refrigerant liquid retained in the condenser64is circulated via a heat exchanger for heat release81through the second circulation path8. For example, in the case where the refrigeration cycle apparatus10is an air conditioner for cooling an indoor space, the heat exchanger for heat release81is placed outside the indoor space, and heats outdoor air supplied by an air blower through heat exchange with the refrigerant liquid.

The refrigeration cycle apparatus10need not necessarily be an air conditioner designed specifically for cooling. For example, if a first heat exchanger placed in an indoor space and a second heat exchanger placed outside the indoor space are connected to the evaporator66and the condenser64via four-way valves, an air conditioner capable of switching between cooling operation and heating operation can be obtained. In this case, both the first heat exchanger and the second heat exchanger function as the heat exchanger for heat absorption71and the heat exchanger for heat release81. In addition, the refrigeration cycle apparatus10need not necessarily be an air conditioner, and may be, for example, a chiller. Furthermore, the object to be cooled in the heat exchanger for heat absorption71and the object to be heated in the heat exchanger for heat release81may be a gas other than air or a liquid.

The expansion valve65is one example of a pressure-reducing mechanism that reduces the pressure of the refrigerant liquid resulting from condensation. However, the pressure-reducing mechanism is not limited to the expansion valve65provided in the main circuit6. For example, a configuration designed to make the level of the refrigerant liquid in the evaporator66higher than the level of the refrigerant liquid in the condenser64may be employed.

In the configuration shown inFIG. 6, the bleed chamber4(seeFIGS. 1 to 4) of the centrifugal compressor1A or1B communicates with the inner space of the evaporator66through the return path9. That is, the inner space of the evaporator66corresponds to the discharge space of the present invention. Therefore, the refrigerant vapor is returned from the bleed chamber4of the centrifugal compressor1A or1B to the evaporator66through the return path9. Thereby, the performance of the centrifugal compressor1A or1B can be enhanced, and as a result, the performance of the refrigeration cycle apparatus10can be enhanced. Desirably, the return path9is provided with a flow rate regulating valve91. The efficiency of the centrifugal compressor1A or1B can be optimized by regulating the flow rate of the refrigerant vapor by the flow rate regulating valve91.

The evaporator66need not necessarily be a direct contact heat exchanger, and it may be an indirect heat exchanger. In this case, a heat medium cooled in the evaporator66circulates through the first circulation path7. Likewise, the condenser64need not necessarily be a direct contact heat exchanger, and it may be an indirect heat exchanger. In this case, a heat medium heated in the condenser64circulates through the second circulation path8.