EP1762793A2

EP1762793A2 - Closed type air cycle refrigerator and cooling method using the same

Info

Publication number: EP1762793A2
Application number: EP06003379A
Authority: EP
Inventors: Masato Mitsuhashi; Seiichi Okuda
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Priority date: 2005-09-09
Filing date: 2006-02-20
Publication date: 2007-03-14
Anticipated expiration: 2026-02-20
Also published as: EP1762793A3; EP1762793B1; NO20060744L; DK1762793T3; JP2007071507A; NO342771B1

Abstract

A closed type refrigerator includes a compressor (3) and an expansion turbine (4) coupled to ends of a rotation shaft of a motor (2), respectively; a refrigerant circulating pipe; a first heat exchanger (5) provided in a portion of the refrigerant circulating pipe from an outlet of the compressor to an inlet of the expansion turbine; and a second heat exchanger (6) provided in a portion of the refrigerant circulating pipe from the first heat exchanger to the inlet of the expansion turbine. The compressor compresses the refrigerant, and the first heat exchanger carries out heat exchange between the compressed refrigerant and atmosphere to generate a first cooled refrigerant. The second heat exchanger carries out heat exchange between the first cooled refrigerant and a second cooled refrigerant to generate a third cooled refrigerant, and the expansion turbine adiabatically expands the third cooled refrigerant to generate the second cooled refrigerant, which is used to cool a refrigeration storage (7) and supplied to the inlet of the compressor. The refrigerant is dehumidified.

Description

Background of the Invention

1. Field of the Invention

The present invention relates to a closed type air refrigerant refrigerator, more particularly, to a closed type air refrigerant refrigerator and a cooling method using the same.

2. Description of the Related Art

Many conventional air refrigerant refrigerators of an opened type are present, in which air is directly sucked from the atmosphere into the refrigerator and the sucked air is used as refrigerant. Fig. 1 is a schematic diagram showing a configuration of the conventional opened type air refrigerant refrigerator (direct cooling type). In the conventional opened type air refrigerant refrigerator 1, a compressor 3 compresses air refrigerant sucked from the atmosphere. A first heat exchanger 5 carries out heat exchange between the air compressed by the compressor 3 and an atmosphere, and a second heat exchanger 6 further cools the air refrigerant cooled by the first heat exchanger by carrying out heat exchange with a low temperature air refrigerant outputted from a refrigeration storage. An expansion turbine 4 adiabatically expands the cooled air cooled by the second hear exchanger 6 and further cools the cooled air. The compressor 3 and the expansion turbine 4 are fixed to a rotational shaft of a motor 2. As shown in Fig. 1, in the conventional opened type air refrigerant refrigerator 1, the air as the refrigerant sucked from the atmosphere is directly cooled and the cooled air refrigerant keeps a refrigeration target 7 such as refrigeration objects cool. Generally, the refrigeration target 7 has a door 7a, and refrigeration objects are carried in or out through the door 7a. Thus, air within the refrigeration target 7 is replaced with outside air as appropriate.
Especially, immediately after the air refrigerant is discharged from the expansion turbine 4, moisture contained in the air refrigerant forms dew and thus frost and ice are adhered to the inner wall surface of a pipe for carrying the air refrigerant. For this reason, a filter (defroster) 8 is attached in the pipe to remove the frost and the ice. When the filter is clogged because of the frost and ice adhered thereto, or in order to prevent clogging of the filter, it is necessary to stop the cooling operation to the refrigerator and remove the frost and ice accumulated on the filter (defroster) 8. As a result, a time period is generated during which the air refrigerant cannot be supplied to the refrigeration storage, thereby causing a problem that the refrigerator is unsuitable for storage of objects such as specific drugs and living bodies required to be constantly cooled in the refrigeration storage.
In conjunction with the above description, the following report is made. In "Guidelines for the Application and Design of Air Cycle Systems for Heating, Ventilating, and Air Conditioning in Buildings", a closed type air refrigerant refrigerator 10 shown in Fig. 2 is proposed. In the closed type air refrigerant refrigerator 10, prior to start of the refrigerator, air as refrigerant is taken into a circulating line 18 of the air refrigerant from the atmosphere via a shut valve 19. In the closed type refrigerant refrigerator 10, a compressor 13 compresses the air refrigerant sucked from the atmosphere. A first heat exchange system 15 carries out heat exchange between the air compressed by the compressor 13 and the atmospheric, and a second heat exchange system 16 further cools the air refrigerant cooled by the first heat exchange system 15 by carrying out heat exchange with low temperature air refrigerant outputted from a refrigeration storage 17. An expansion turbine 12 adiabatically expands the air refrigerant cooled by the second hear exchanger 16 and cools the air refrigerant to about -75°C. The compressor 13 and the expansion turbine 12 are rotated with a driving force by a motor 11. As shown in Fig. 2, in this conventional closed type air refrigerant refrigerator shown in Fig. 2, the air refrigerant is taken from the atmosphere into a pipe line and is hermetically closed in the pipe line 18 to have a pressure corresponding to an operating environment. A refrigeration storage 17 is kept due to the cooled air refrigerant via a third heat exchange system 14. Thus, the closed type air refrigerant refrigerator 10 can carry out a stable cooling operation without being affected by the operation environment such as atmospheric pressure and change in atmospheric pressure).

Summary of the Invention

An object of the present invention is to provide a closed type air refrigerant refrigerator, which uses dry air or nitrogen gas containing no moisture and has a mechanism for preventing refrigerant filled in a pipe from directly contacting atmosphere.
In an aspect of the present invention, a closed type refrigerator includes a motor having a rotation shaft; a compressor coupled to one end of the rotation shaft; an expansion turbine coupled to the other end of the rotation shaft; a refrigerant circulating pipe configured to circulate a refrigerant from an outlet of the compressor and an inlet of the expansion turbine and from an outlet of the expansion turbine to an inlet of the compressor to form a closed loop for a flow route of the refrigerant; a first heat exchanger provided in a portion of the refrigerant circulating pipe from the outlet of the compressor to the inlet of the expansion turbine; and a second heat exchanger provided in a portion of the refrigerant circulating pipe from the first heat exchanger to the inlet of the expansion turbine. The compressor compresses the refrigerant, and the first heat exchanger carries out heat exchange between the compressed refrigerant and atmosphere to generate a first cooled refrigerant. The second heat exchanger carries out heat exchange between the first cooled refrigerant and a second cooled refrigerant to generate a third cooled refrigerant, and the expansion turbine adiabatically expands the third cooled refrigerant to generate the second cooled refrigerant, which is used to cool a refrigeration storage and supplied to the inlet of the compressor. The refrigerant is dehumidified and is hermetically closed in the refrigerant circulating pipe such that the refrigerant does not condense even when the refrigerant is cooled to a minimum temperature in the refrigerant circulating pipe.
Here, the refrigerant may be dry air or dry nitrogen.
In this case, the closed type refrigerator may further include a brine heat exchanger provided in a portion of the refrigerant circulating pipe between the outlet of the expansion turbine and the second heat exchanger to carry out heat exchange between the second cooled refrigerant and a brine in a brine line. A portion the brine line is arranged in the refrigeration storage.
Also, a portion of the refrigerant circulating pipe from the outlet of the expansion turbine to the second heat exchanger may be arranged in the refrigeration storage.
In another aspect of the present invention, a method of cooling a refrigeration storage is achieved by compressing a refrigerant by compressor, wherein the compressor is coupled to one end of a rotation shaft of a motor, and the refrigerant is dehumidified and is hermetically closed in a refrigerant circulating pipe such that the refrigerant does not condense even when the refrigerant is cooled to a minimum temperature in the refrigerant circulating pipe; by circulating the compressed refrigerant in the refrigerant circulating pipe to a first heat exchanger; by carrying out heat exchange between the compressed refrigerant and atmosphere by the first heat exchanger to generate a first cooled refrigerant; by circulating the first cooled refrigerant in the refrigerant circulating pipe to a second heat exchanger; by carrying out second heat exchange between the first cooled refrigerant and a second cooled refrigerant by the second heat exchanger to generate a third cooled refrigerant; by adiabatically expanding the third cooled refrigerant by an expansion turbine to generate the second cooled refrigerant, wherein the expansion turbine is coupled to the other end of the rotation shaft of the motor; by cooling a refrigeration storage by using the second cooled refrigerant; and by circulating the second cooled refrigerant to the compressor after the second heat exchange.
Here, the refrigerant may be dry air or dry nitrogen.
Also, the cooling may be achieved by carrying out a brine heat exchange between the second cooled refrigerant and a brine in a brine line between the expansion turbine and the second heat exchanger. A portion the brine line is arranged in the refrigeration storage.
Also, a portion of the refrigerant circulating pipe from the expansion turbine to the second heat exchanger is arranged in the refrigeration storage.

Brief Description of the Drawings

Fig. 1 is a schematic diagram showing a configuration of a conventional opened type air refrigerant refrigerator;
Fig. 2 is a schematic diagram showing the configuration of another conventional closed type air refrigerant refrigerator;
Fig. 3 is a schematic diagram showing the configuration of a closed type air refrigerant refrigerator according to a first embodiment of the present invention;
Fig. 4 is a schematic diagram showing the configuration of the closed type air refrigerant refrigerator according to a second embodiment of the present invention;
Fig. 5 is a table showing cooling performance depending on refrigerants used in a -30°C cooling operation in the closed type air refrigerant refrigerator in the first embodiment;
Fig. 6 is a table showing physical values of air containing moisture and dry air containing no moisture at -30°C and -60°C; and
Fig. 7 is a schematic diagram showing the configuration of the closed type air refrigerant refrigerator according to a third embodiment of the present invention.

Description of the Preferred Embodiments

Hereinafter, a closed type air refrigerant refrigerator according to the present invention will be described in detail with reference to the attached drawings.

[First Embodiment]

Fig. 3 is a schematic diagram showing the configurations of the closed type air refrigerant refrigerator according to the first embodiment of the present invention. The air refrigerant refrigerator 20 is provided with a compressor 3 and an expansion turbine 4. The compressor 3 is coupled to an end of a shaft of a motor 2 and the expansion turbine 4 is coupled to the other end of the shaft. A refrigerant circulating pipe 21 is connected to the inlet of the compressor 3, and connects the outlet of the compressor 3 to the inlet of the expansion turbine 4 through a first heat exchanger 5 and a second heat exchanger 6. Also, the refrigerant circulating pipe 21 connects the outlet of the expansion turbine 4 to the inlet of the compressor 3 through a brine cooler (heat exchanger) 22 and the second heat exchanger 6. In the refrigerant circulating pipe 21, dry air or dry nitrogen is hermetically sealed.
The compressor 3 compresses air refrigerant taken into the refrigerant circulating pipe 21 from the atmosphere and supplied thereto, and outputs the compressed air to the first heat exchanger 5. The first heat exchanger 5 is supplied with the atmospheric air by a pump P and carries out heat exchange between the air refrigerant compressed by the compressor 3 and an atmospheric air to cool the compressed air refrigerant. The compressed air refrigerant cooled by the first heat exchanger 5 is supplied to the second heat exchanger 6. The second heat exchanger 6 carries out heat exchange between the air refrigerant cooled by the first heat exchanger 5 and low temperature air refrigerant in the refrigerant circulating pipe 21 outputted from the brine cooler 22. The air refrigerant cooled by the second heat exchanger 6 is supplied to the expansion turbine 4. The expansion turbine 4 adiabatically expands the air refrigerant cooled by the second hear exchanger 6, resulting in the air refrigerant being further cooled to about -80°C. The air refrigerant cooled by the expansion turbine 4 is supplied to the brine cooler 22. Brine circulated in a brine line 23 is cooled in the brine cooler 22 with the air refrigerant cooled by the expansion turbine 4. The cooled brine is circulated in the brine line 23 by a pump P and cools a refrigeration storage 7, in which refrigeration objects are stored. The air refrigerant outputted from the brine cooler 22 is used to carry out the heat exchange in the second heat exchanger 6 and then is supplied to the inlet of the compressor 3.
In the present embodiment, prior to start of the refrigerator 20, the refrigerant circulating pipe 21 is filled with dry air or dry nitrogen. The dry air or dry nitrogen is taken into the refrigerant circulating pipe 21. At this time, the air or nitrogen is dehumidified to the extent that condensation does not occur in the refrigerant circulating pipe 21 even when its temperature becomes lowest. Thus, the dry air or dry nitrogen is introduced in the refrigerant circulating pipe 21. Here, the following method is employed as a method of replacing normal air with the dry air or dry nitrogen in the refrigerant circulating line 21. That is, the dry air or the dry nitrogen is introduced from a valve (not shown) provided in a lower pressure portion of the refrigerant circulating pipe 21, for example, in front of the second heat exchanger 6, and is circulated in the refrigerant circulating pipe 21. Then, air mixed with the dry air or dry nitrogen is discharged from a valve (not shown) provided in a higher pressure portion of the refrigerant circulating pipe 21, for example, in front of an inlet of the expansion turbine 4. Using a hygrometer, the above-mentioned procedure is repeatedly carried out until a humidity in the refrigerant circulating pipe 21 reaches a predetermined value at which condensation does not occur in the refrigerant circulating pipe 21 even under the lowest temperature of the air or nitrogen.
It should be noted that in the closed type air refrigerant refrigerator 20 in the first embodiment, the refrigeration storage 7 may be any of the following storages:

(A) a refrigerator for freezing refrigeration objects;
(B) a freezing-drying furnace for freezing-drying refrigeration objects;
(C) a chemical reactor for keeping specific chemical and medical products;
(D) a low-temperature laboratory;
(E) a container box when the closed type air refrigerant refrigerator is formed to be transportable as a reflex container; and
(F) a car-mounted refrigerator when the closed type air refrigerant refrigerator is formed of a car-mounted refrigerator.

Next, the refrigeration performance when the dry air or the dry nitrogen is used as the refrigerant will be described in comparison with that in the conventional example where air containing moisture is used as the refrigerant.
Hereinafter, the refrigeration performance when the dry air or the dry nitrogen is used as the refrigerant in the closed type air refrigerant refrigerator 20 for -30°C refrigeration storage 7 will be described. The following parameter values are assumed as a condition to be considered (pipe pressure loss is not considered).
Stockroom temperature: -30 [°C]
Compressor efficiency: 0.80
Turbine efficiency: 0.85
Compressor inlet temperature: 36 [°C]
Expansion turbine inlet temperature: -24 [°C] (Compressor/expansion turbine) pressure ratio: 1.99 The following values are used as physical property values of air and nitrogen.
[Air physical property values]
Specific heat: 1.005 [kJ/kgK]
Density: 1.293 [kg/m³]
Specific heat ratio: 1.4
[Nitrogen physical property values]
Specific heat: 1.040 [kJ/kgK]
Density: 1.250 [kg/m³]
Specific heat ratio: 1.4
Here, compressor power Wc [kW], turbine power Wt [kW], refrigeration performance Wc [kW] and turbine outlet temperature Tt [°C] are represented by the following equations (1) to (3). $Wc = \frac{1}{0.80} \times Cp \times (273.15 + 36) \times ({1.99}^{\frac{K - 1}{K}} - 1) [kW / kg]$
$Wt = 0.85 \times Cp \times (273.15 - 24) \times (1 - {(\frac{1}{1.99})}^{\frac{K - 1}{K}}) [kW / kg]$
$\begin{matrix} Wt = Cp \times (- 24 - T_{t}) & ∴ T_{t} = - (\frac{Wt}{Cp} + 24) [°C] \end{matrix}$
A Coefficient of Performance (COP) in the closed type air refrigerant refrigerator 20 in the first embodiment is shown in the following equation (4). $COP = \frac{Cp \times (- 30 - t_{t})}{Wc - Wt}$

Also, a refrigerant flow rate G necessary for 10 RT is shown by the following equation (5). $\begin{matrix} 38.6 = Cp \times (- 30 - T_{t}) G, & ∴ G = \frac{38.6}{Cp \times (- 30 - t_{t})} [kg / s] \end{matrix}$

(Cp: specific heat, G: flow rate, k: specific heat ratio, p: density)
When the above-mentioned physical property values for each refrigerant are substituted into the above-mentioned equations, calculation results shown in Fig. 5 are obtained. However, in calculation of the refrigeration performance of the dry air, the specific heat is assumed to be constant.
Also, the refrigeration performance when air containing moisture as the conventional refrigerant is used, can be obtained by calculating a quantity of heat required to lower the air temperature from -30 [°C] to -62 [°C] and regarding the quantity of heat as degradation in refrigeration performance. Thus, calculation results shown in Fig. 6 are obtained. That is, the quantity of heat [per unit refrigerant low rate (1 [kg/s])] required to lower the air temperature from -30 [°C] to -62 [°C] is as follows in each of saturated wet air and the dry air:

Saturated wet air: -29.57 - (-62.29) = 32.72 [kW]
Dry air: -30.14 - (-62.29) = 32.15 [kW].

0.57 / 32.15 \times 100 = 1.78 [%]

It could be understood from the above-mentioned results that even if the air refrigerant containing moisture used as the conventional refrigerant is replaced with the dry air or nitrogen containing no moisture, the refrigeration performance is almost unchanged. Furthermore, in the first embodiment, by removing the moisture from the refrigerant, no frost is adhered to the refrigerant circulating pipe 21 and other components in the refrigerator, thereby preventing degradation in functions of the refrigerator due to rust. As a result, reliability of the closed type air refrigerant refrigerator according to the present embodiment can be improved.
As described above, the closed type air refrigerant refrigerator in the first embodiment invention has a mechanism to prevent refrigerant filled in a refrigerant circulating pipe in the refrigerator from directly contacting atmosphere. Also, dry air or dry nitrogen as the refrigerant is dehumidified to the extent that condensation does not occur in the refrigerant circulating pipe even when its temperature becomes lowest. Thus, it is unnecessary to install a filter for removing frost and ice generated through condensation of moisture contained in the air refrigerant, which occurs during the cooling operation of the air refrigerant in a conventional air refrigerant refrigerator. Thus, manufacturing and maintenance costs of the air refrigerant refrigerator can be reduced. In addition, in the air refrigerant refrigerator of the first embodiment, it is not necessary to stop the operation of the refrigerator because of cleaning of the filter and defrosting. Furthermore, manufacturing and maintenance costs of the air refrigerant refrigerator can be reduced. For these reasons, a continuous cooling operation of refrigeration targets such as specific drugs and living bodies becomes possible, which must be kept under a cooling condition at all times. Furthermore, in the first embodiment, by using the refrigerant containing no moisture, generation of rust in the refrigerator can be prevented and the reliability of the refrigerator itself can be improved.

[Second Embodiment]

Fig. 4 is a schematic diagram showing the configuration of the closed type air refrigerant refrigerator according to the second embodiment of the present invention. The closed type air refrigerant refrigerator of the second embodiment is different from that of the first embodiment in a cooling method of the refrigeration storage 7. In the second embodiment, a brine line 24 is used in addition to the brine line 23 in the first embodiment. The brine line 24 is connected to the brine line 23 through shut valves.
The operation and advantages of the closed type air refrigerant refrigerator in the second embodiment are the same as those of the refrigerator in the first embodiment. Therefore, the description is omitted.

[Third Embodiment]

Fig. 7 is a schematic diagram showing the configuration of the closed type air refrigerant refrigerator 40 according to the third embodiment of the present invention. The basic configuration and operating principle of the closed type air refrigerant refrigerator 40 in the third embodiment are the same as those of the refrigerator in the first embodiment. Therefore, the description thereof is omitted. In the third embodiment, however, the brine cooler 22 provided in the first embodiment is not provided. Instead, the refrigerant circulating pipe 21 is directly arranged in the refrigeration storage 7. By circulating the cooled air refrigerant in the refrigerant circulating pipe 21 disposed in the refrigeration storage 7, the temperature in the refrigeration storage 7 is lowered, thereby keeping the refrigeration objects stored in the refrigeration storage 7 cool.
Also, in the third embodiment, a refrigerant is filled in the refrigerant circulating pipe 21 prior to start of the refrigerator 40, as in the first embodiment. The dry air or the dry nitrogen is used as the refrigerant filled in the refrigerant circulating pipe 21. In the third embodiment, since the inside of the refrigeration storage 7 is directly cooled, manufacturing and maintenance costs can be further reduced as compared with the first embodiment.
Also, in the third embodiment, as in the first embodiment, it is unnecessary to install a filter for removing frost and ice generated through condensation of moisture contained in the air refrigerant. Thus, the operation of the refrigerator is not stopped because of cleaning of the filter and defrosting. For these reasons, a continuous cooling operation of the refrigeration objects such as specific drugs and living bodies becomes possible, which must be kept under cooling condition at all times. In addition, in the third embodiment, manufacturing and maintenance costs of the air refrigerant refrigerator can be reduced. Also, by using the refrigerant containing no moisture, rust can be prevented from occurring in the refrigerator and thus the reliability of the refrigerator itself can be improved.
It should be noted that in the closed type air refrigerant refrigerator 40 according to the third embodiment, the refrigeration storage 7 may be the objects described in the first embodiment.

Claims

A closed type refrigerator comprising:
a motor (2) having a rotation shaft;

a compressor (3) coupled to one end of said rotation shaft;

an expansion turbine (4) coupled to the other end of said rotation shaft;

a refrigerant circulating pipe configured to circulate a refrigerant from an outlet of said compressor and an inlet of said expansion turbine and from an outlet of said expansion turbine to an inlet of said compressor to form a closed loop for a flow route of said refrigerant;

a first heat exchanger (5) provided in a portion of said refrigerant circulating pipe from the outlet of said compressor to the inlet of said expansion turbine; and

a second heat exchanger (6) provided in a portion of said refrigerant circulating pipe from said first heat exchanger to the inlet of said expansion turbine,
wherein said compressor compresses said refrigerant,
said first heat exchanger carries out heat exchange between the compressed refrigerant and atmosphere to generate a first cooled refrigerant,
said second heat exchanger carries out heat exchange between the first cooled refrigerant and a second cooled refrigerant to generate a third cooled refrigerant,
said expansion turbine adiabatically expands the third cooled refrigerant to generate the second cooled refrigerant, which is used to cool a refrigeration storage (7) and supplied to the inlet of said compressor, and
said refrigerant is dehumidified and is hermetically closed in said refrigerant circulating pipe such that said refrigerant does not condense even when said refrigerant is cooled to a minimum temperature in said refrigerant circulating pipe.
The closed type refrigerator according to claim 1, wherein said refrigerant is dry air.
The closed type refrigerator according to claim 1, wherein said refrigerant is dry nitrogen.
The closed type refrigerator according to any of claims 1 to 3, further comprising:
a brine heat exchanger provided in a portion of said refrigerant circulating pipe between the outlet of said expansion turbine and said second heat exchanger to carry out heat exchange between said second cooled refrigerant and a brine in a brine line,
wherein a portion said brine line is arranged in said refrigeration storage.
The closed type refrigerator according to any of claims 1 to 3, wherein a portion of said refrigerant circulating pipe from the outlet of said expansion turbine to said second heat exchanger is arranged in said refrigeration storage.
A method of cooling a refrigeration storage, comprising:
compressing a refrigerant by compressor,
wherein said compressor is coupled to one end of a rotation shaft of a motor, and said refrigerant is dehumidified and is hermetically closed in a refrigerant circulating pipe such that said refrigerant does not condense even when said refrigerant is cooled to a minimum temperature in said refrigerant circulating pipe;
circulating the compressed refrigerant in said refrigerant circulating pipe to a first heat exchanger;
carrying out heat exchange between the compressed refrigerant and atmosphere by said first heat exchanger to generate a first cooled refrigerant;
circulating the first cooled refrigerant in said refrigerant circulating pipe to a second heat exchanger;
carrying out second heat exchange between the first cooled refrigerant and a second cooled refrigerant by said second heat exchanger to generate a third cooled refrigerant;
adiabatically expanding the third cooled refrigerant by an expansion turbine to generate the second cooled refrigerant, wherein said expansion turbine is coupled to the other end of said rotation shaft of said motor;
cooling a refrigeration storage by using the second cooled refrigerant; and
circulating the second cooled refrigerant to said compressor after said second heat exchange.
The method according to claim 6, wherein said refrigerant is dry air.
The method according to claim 6, wherein said refrigerant is dry nitrogen.
The method according to any of claims 6 to 8, wherein said cooling comprises:
carrying out a brine heat exchange between the second cooled refrigerant and a brine in a brine line between said expansion turbine and said second heat exchanger,
wherein a portion said brine line is arranged in said refrigeration storage.
The method according to any of claims 6 to 8,
wherein a portion of said refrigerant circulating pipe from said expansion turbine to said second heat exchanger is arranged in said refrigeration storage.