TURBO REFRIGERATOR

Abstract

A turbo refrigerator includes a condenser that cools and liquefies a compressed refrigerant, an evaporator that vaporizes the liquefied refrigerant and takes away heat of vaporization from a cooling object, thereby cooling the cooling object, and a turbo compressor that compresses the refrigerant vaporized by the evaporator by rotation of an impeller driven to rotate by an electric motor, and supplies the compressed refrigerant to the condenser. Moreover, the turbo refrigerator includes a braking device that operates the electric motor as a generator when the impeller is urged to rotate by the vaporized refrigerant, so as to brake the rotation of the impeller.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a turbo refrigerator.

Priority is claimed on Japanese Patent Application No. 2010-092314, filed on Apr. 13, 2010, the content of which is incorporated herein by reference.

2. Description of Related Art

As a refrigerator that cools or freezes cooling objects such as water, a turbo refrigerator having a turbo compressor that compresses and discharges a refrigerant in a gaseous state is known (for example, refer to Japanese Patent Application, Publication No. 2007-177695). The turbo compressor compresses the refrigerant by the rotation of an impeller which is driven to rotate by an electric motor.

The refrigerant compressed by the turbo compressor is supplied to a condenser and then is cooled and liquefied. The liquefied refrigerant is supplied to an evaporator and is thus vaporized by the evaporator. The refrigerant takes away heat of vaporization from a cooling object when vaporized, thereby cooling the cooling object. The vaporized refrigerant is supplied to the turbo compressor again.

And now, when the turbo refrigerator is stopped (for example, at the time of an emergency stop), the liquefied refrigerant which is stored in the condenser vaporizes and flows back to the turbo compressor. Therefore, there is a possibility of the impeller of the turbo compressor being urged to reverse by the vaporized refrigerant. When the impeller is reversed, there is a possibility of the turbo compressor breaking down due to vibration or the like caused by the reversal. In order to prevent the reversal of the impeller, a configuration in which a check valve is installed in the flow path between the condenser and the turbo compressor to prevent a flow of the refrigerant toward the turbo compressor from the condenser, is generally used.

However, when the check valve is installed in the flow path, flow resistance against the refrigerant is increased, so that a pressure drop caused by the flow of the refrigerant is increased. When the pressure drop is increased, during normal operation, the freezing capability of the turbo refrigerator is degraded.

In consideration of the problem, an object of the invention is to provide a turbo refrigerator capable of preventing or suppressing reversal of a turbo compressor, thereby reducing a pressure drop caused by the flow of the refrigerant.

SUMMARY OF THE INVENTION

In order to accomplish the object, the invention employs the following means.

A turbo refrigerator related to the invention includes a condenser that cools and liquefies a compressed refrigerant, an evaporator that vaporizes the liquefied refrigerant and takes away the heat of vaporization from a cooling object, thereby cooling the cooling object, and a turbo compressor that compresses the refrigerant vaporized by the evaporator by rotation of an impeller driven to rotate by an electric motor, and supplies the compressed refrigerant to the condenser. Moreover, the turbo refrigerator related to the invention includes a braking device that operates the electric motor as a generator when the impeller is urged to rotate by the vaporized refrigerant, so as to brake the rotation of the impeller.

As described above, when the turbo refrigerator is stopped, the liquefied refrigerant stored in the condenser vaporizes and flows back to the turbo compressor. Therefore, there is a possibility of the impeller of the turbo compressor being urged to reverse by the vaporized refrigerant. According to the invention, when the impeller is urged to reverse by the refrigerant, the braking device operates the electric motor as a generator. When the electric motor is operated as a generator, rotational resistance against the rotation of the impeller occurs. Using the rotational resistance, the reversal of the impeller is braked.

In addition, in the turbo refrigerator related to the invention, the braking device may have a regeneration circuit that recovers electrical energy generated by the electric motor.

In addition, in the turbo refrigerator related to the invention, the braking device may have a resistance circuit that converts the electrical energy generated by the electric motor into heat energy.

According to the invention, since the braking device operates the electric motor as a generator, the reversal of the impeller is braked. Accordingly, the reversal of the turbo compressor can be prevented or suppressed. Moreover, as the braking device is provided, the reversal of the turbo compressor is prevented or suppressed. Therefore, a check valve is excluded from the turbo refrigerator. Therefore, a pressure drop caused by the flow of the refrigerant is suppressed to be low, so that the freezing capability of the turbo refrigerator is enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a skeleton framework of a turbo refrigerator according to an embodiment of the invention.

FIG. 2 is a block diagram showing an operation when the turbo refrigerator is stopped according to the embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, exemplary embodiments of the invention will be described with reference to FIGS. 1 to 2. As well, in the drawings used for the following description, in order to allow each member to have a recognizable size, the scale of each member is appropriately changed.

FIG. 1 is a block diagram showing a skeleton framework of a turbo refrigerator 1 according to an embodiment of the invention.

The turbo refrigerator 1 according to this embodiment is installed, for example, at a building, a factory, or the like in order to generate cooling water for air-conditioning. In addition, the turbo refrigerator 1 in this embodiment includes a turbo compressor 2, an inverter 3 (braking device), a condenser 4, and an evaporator 5.

The turbo compressor 2 is a member that compresses a refrigerant gas X1 which is a refrigerant in a gaseous state to generate a compressed refrigerant gas X2. A first flow path R1 through which the refrigerant gas X1 flows and a second flow path R2 through which the compressed refrigerant gas X2 flows are connected to the turbo compressor 2. The turbo compressor 2 includes an impeller 21 and a motor 22 (electric motor).

The impeller 21 is an impeller used for compressing the refrigerant gas X1. The refrigerant gas X1 is introduced to the impeller 21 via an intake (not shown) formed in a rotation axis line direction (thrust direction) of the impeller 21. The introduced refrigerant gas X1 is sent outward in the radial direction by the rotating impeller 21. On the outside of the impeller 21 in the radial direction, a diffuser and a scroll chamber (not shown) are formed. In addition, the refrigerant gas X1 is compressed as flowing inside the diffuser and the scroll chamber, thereby generating the compressed refrigerant gas X2. The first flow path R1 is connected to the above-mentioned intake, and the second flow path R2 is connected to the scroll chamber.

The motor 22 is a driving device for rotating the impeller 21. The motor 22 is an AC electric motor (three phase type) that is driven as AC power is supplied thereto. In addition, the rotational speed of the motor 22 can be changed by adjusting the frequency of the supplied AC power. The motor 22 is integrally connected to the impeller 21 via a rotation shaft 23. The rotation shaft 23 is supported so as to be rotatable via a rolling bearing (a ball bearing, a roller bearing, or the like) (not shown). Moreover, the rolling bearing is a member for ensuring smooth rotation of the rotation shaft 23 in either of the forward and reverse rotation directions.

The inverter 3 is an electronic device which drives the motor 22 of the turbo compressor 2 and brakes the reversal (rotation in a direction opposite to rotation during a general cooling operation) of the impeller 21. The inverter 3 is connected to a main power supply system P that supplies power for operating the turbo refrigerator 1 and the motor 22 via the respective power supply lines. The inverter 3 includes a driving circuit 31 and a regeneration circuit 32. The driving circuit 31 and the regeneration circuit 32 have a configuration in which they are not simultaneously operated and operations thereof are switched on the basis of a signal (for example, a signal indicating a stop (an emergency stop or the like) of the turbo refrigerator 1) input to the inverter 3.

The driving circuit 31 is a circuit for driving the motor 22 by supplying the AC power to the motor 22 from the main power supply system P. In addition, the driving circuit 31 can adjust the frequency of the AC power supplied to the motor 22. As the driving circuit 31 adjusts the frequency of the AC power, the rotational speed of the motor 22 is changed. In addition, the compression capability of the turbo compressor 2 and the cooling capability of the turbo refrigerator 1 are adjusted. Moreover, the driving circuit 31 may also be a circuit that adjusts the voltage as well as the frequency of the AC power.

The regeneration circuit 32 is a circuit that brakes the reversal of the impeller 21 to prevent or suppress the reversal of the turbo compressor 2. In addition, the regeneration circuit 32 is provided in parallel with the driving circuit 31. The regeneration circuit 32 is a circuit for operating the motor 22 as a generator when the motor 22 is reversed by the reversal of the impeller 21. In addition, the regeneration circuit 32 recovers electrical energy generated by the motor 22 which is operated as a generator and supplies the electrical energy to the main power supply system P (regeneration operation). Moreover, a configuration in which the electrical energy recovered by the regeneration circuit 32 is stored in a storage batter or the like may be employed. In addition, the regeneration circuit 32 is configured as a braking device separately from the inverter 3 so as to be installed in parallel with the inverter 3.

The condenser 4 is a heat exchanger that cools and liquefies the compressed refrigerant gas X2 to generate a refrigerant liquid X3. The second flow path R2 through which the compressed refrigerant gas X2 flows and a third flow path R3 through which the refrigerant liquid X3 flows are connected to the condenser 4. Moreover, in the third flow path R3, an expansion valve 6 for reducing the pressure of the refrigerant liquid X3 is installed.

The evaporator 5 is a heat exchanger that takes away heat of vaporization from a cooling object such as water or the like by vaporizing the refrigerant liquid X3 for cooling the cooling object. Moreover, the refrigerant liquid X3 vaporized by the evaporator 5 is changed into the refrigerant gas X1. The third flow path R3 through which the refrigerant liquid X3 flows and the first flow path R1 through which the refrigerant gas X1 flows are connected to the evaporator 5.

In the turbo refrigerator 1, the first flow path R1, the second flow path R2, and the third flow path R3 form circulation flow paths of the refrigerant (the refrigerant gas X1, the compressed refrigerant gas X2, and the refrigerant liquid X3).

Next, a freezing operation of the turbo refrigerator 1 will be described with reference to FIG. 1.

The driving circuit 31 of the inverter 3 supplies the AC power to the motor 22 of the turbo compressor 2 from the main power supply system P. The motor 22 is driven as the AC power is supplied, and the impeller 21 connected thereto via the rotation shaft 23 is rotated. As the impeller 21 is rotated, the refrigerant gas X1 inside the first flow path R1 is sucked to be introduced to the impeller 21. The introduced refrigerant gas X1 is sent outward in the radial direction of the impeller 21 and then is compressed by flowing into the diffuser and the scroll chamber (not shown), and is thus changed into the compressed refrigerant gas X2. The compressed refrigerant gas X2 is sent to the second flow path R2 connected to the scroll chamber.

The compressed refrigerant gas X2 is introduced to the condenser 4 via the second flow path R2. The compressed refrigerant gas X2 is cooled and liquefied by the condenser 4 so as to be changed into the refrigerant liquid X3. The refrigerant liquid X3 is sent to the third flow path R3 and is decompressed by the expansion valve 6.

The refrigerant liquid X3 decompressed by the expansion valve 6 is introduced to the evaporator 5. The refrigerant liquid X3 is vaporized by the evaporator 5, and thus the refrigerator X3 takes away heat of vaporization from the cooling object such as water or the like, thereby cooling the cooling object. When the refrigerant liquid X3 is vaporized, the refrigerant liquid X3 is changed into the refrigerant gas X1, and the refrigerant gas X1 is sent to the first flow path R1. The refrigerant gas X1 is introduced again to the turbo compressor 2 via the first flow path R1.

As such, the freezing operation of the turbo refrigerator 1 is completed.

Subsequently, an operation performed when the turbo refrigerator 1 is stopped is described with reference to FIG. 2. FIG. 2 is a block diagram showing an operation performed when the turbo refrigerator 1 is stopped according to this embodiment.

For example, a situation in which a device included in the turbo refrigerator 1 has a problem and the turbo refrigerator 1 is stopped in an emergency will be described. When the turbo refrigerator 1 is stopped in an emergency, a signal indicating an emergency stop is input to the inverter 3. In addition, the driving circuit 31 of the inverter 3 stops supplying the AC power, so that the driving of the motor 22 is stopped. As the motor 22 is stopped, the rotation of the impeller 21 is stopped, so that discharge of the compressed refrigerant gas X2 to the second flow path R2 is stopped. Therefore, the introduction of the compressed refrigerant gas X2 to the condenser 4 is stopped.

As the introduction of the compressed refrigerant gas X2 to the condenser 4 is stopped, the refrigerant liquid X3 stored in the condenser 4 vaporizes and flows back to the second flow path R2. As well, the refrigerant gas produced by vaporization of the refrigerant liquid X3 tries to flow into the third flow path R3. However, since the flow resistance of the expansion valve 6 installed in the third flow path R3 is high, the refrigerant gas produced by vaporization of the refrigerant liquid X3 mostly flows into the second flow path R2 and is changed into a backflow refrigerant gas X4.

The backflow refrigerant gas X4 flows through the second flow path R2 toward the turbo compressor 2 and is introduced to the turbo compressor 2. The backflow refrigerant gas X4 is introduced to the impeller 21 from the outside thereof in the radial direction via the scroll chamber and the diffuser (not shown) of the turbo compressor 2. The backflow refrigerant gas X4 introduced to the impeller 21 causes the impeller 21 to be urged to reverse. Here, the rotation shaft 23 is supported via the rolling bearing (not shown), and the rolling bearing smoothly rotates the rotation shaft 23 in either of the forward and reverse rotation directions. Therefore, the rotation shaft 23 connected to the impeller 21 is smoothly reversed. Therefore, the motor 22 connected to the impeller 21 via the rotation shaft 23 is also reversed.

On the other hand, as the signal indicating an emergency stop is input to the inverter 3, the regeneration circuit 32 is operated instead of the driving circuit 31. The regeneration circuit 32 operates the motor 22 as a generator.

That is, when the impeller 21 is urged to reverse by the backflow refrigerant gas X4, the regeneration circuit 32 operates the motor 22 as a generator. When the motor 22 is operated as a generator, rotational resistance against the reversal of the impeller 21 occurs. In addition, as the rotational resistance occurs, the reversal of the impeller 21 is braked. When the urging force caused by the flow of the backflow refrigerant gas X4 is smaller than the rotational resistance against the impeller 21 caused by the motor 22, the reversal of the impeller 21 is stopped. In addition, when the urging force caused by the flow of the backflow refrigerant gas X4 is larger than the rotational resistance, the reversal of the impeller 21 is suppressed. As a result, the reversal of the turbo compressor 2 is prevented or suppressed, so that vibration or the like caused by the reversal is prevented, thereby preventing problems such as a breakdown of the turbo compressor 2 or noise.

When the impeller 21 is reversed as being urged by the backflow refrigerant gas X4, the motor 22 that is operated as a generator generates electrical energy. The regeneration circuit 32 recovers the electrical energy generated by the motor 22 and supplies the electrical energy to the main power supply system P. That is, the flow energy of the backflow refrigerant gas X4 is reused.

As well, in this embodiment, the inverter 3 has the regeneration circuit 32. However, instead of the regeneration circuit 32, the inverter 3 may have a resistance circuit. The resistance circuit is a circuit that operates the motor 22 as a generator when the impeller 21 is reversed and converts electrical energy generated by the motor 22 into heat energy. The regeneration circuit 32 supplies the electrical energy generated by the motor 22 to the main power supply system P. However, when the voltage generated by the motor 22 is lower than the voltage in the main power supply system P, the electrical energy generated by the motor 22 cannot be supplied to the main power supply system P (cancellation of regeneration). When cancellation of regeneration occurs, the rotational resistance against the impeller 21 insufficiently occurs. Therefore, it is possible to obtain a stable braking operation by using the resistance circuit. As well, when the resistance circuit is used, the electrical energy is converted into heat energy and is dissipated. In addition, a configuration in which the inverter 3 has both the regeneration circuit 32 and the resistance circuit and selects an operating circuit from the regeneration circuit 32 and the resistance circuit in response to the voltage generated by the motor 22 may also be employed.

As such, the operation performed when the turbo refrigerator 1 is stopped is completed.

As described above, the inverter 3 according to this embodiment has the regeneration circuit 32. Accordingly, the reversal of the impeller 21 is braked, so that the reversal of the turbo compressor 2 is prevented or suppressed. Therefore, the check valve installed in the second flow path R2 to prevent the flow of the backflow refrigerant gas X4 is excluded from the turbo refrigerator 1. As the check valve is excluded from the second flow path R2, the flow resistance of the second flow path R2 itself is reduced, so that a pressure drop that occurs when the compressed refrigerant gas X2 flows through the second flow path R2 is suppressed to be low. As the pressure drop caused by the flow of the compressed refrigerant gas X2 is suppressed to be low, the freezing capability of the turbo refrigerator 1 is enhanced.

Therefore, according to this embodiment, the following effects can be obtained.

According to this embodiment, as the inverter 3 operates the motor 22 as a generator, the rotation of the impeller 21 is braked. Therefore, the reversal of the turbo compressor 2 is prevented or suppressed. As the inverter 3 is provided, the reversal of the turbo compressor 2 is prevented or suppressed. Therefore, the check valve is excluded from the turbo refrigerator 1. Therefore, the pressure drop caused by the flow of the compressed refrigerant gas X2 is suppressed to be low, so that the freezing capability of the turbo refrigerator 1 is enhanced.

While the exemplary embodiments related to the invention have been described with reference to the accompanying drawings, the invention is not limited to the related embodiments. The shapes and combinations of the constituent members described in the above embodiments are only examples and can be modified in various manners depending on design requirements without departing from the spirit and scope of the invention.

For example, in the above embodiments, the turbo compressor 2 is a single-stage compressor having only the impeller 21. However, the invention is not limited to this configuration, and a multi-stage compressor having a plurality of impellers may also be employed.

While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.

Claims

1. A turbo refrigerator comprising:

a condenser that cools and liquefies a compressed refrigerant;

an evaporator that vaporizes the liquefied refrigerant and takes away heat of vaporization from a cooling object, thereby cooling the cooling object;

a turbo compressor that compresses the refrigerant vaporized by the evaporator by rotation of an impeller driven to rotate by an electric motor, and supplies the compressed refrigerant to the condenser; and

a braking device that operates the electric motor as a generator when the impeller is urged to rotate by the vaporized refrigerant, so as to brake the rotation of the impeller.

2. The turbo refrigerator according to claim 1, wherein the braking device has a regeneration circuit that recovers electrical energy generated by the electric motor.

3. The turbo refrigerator according to claim 1, wherein the braking device has a resistance circuit that converts the electrical energy generated by the electric motor into heat energy.

4. The turbo refrigerator according to claim 2, wherein the braking device has a resistance circuit that converts the electrical energy generated by the electric motor into heat energy.