JP2009002564A - Refrigerant cooling circuit - Google Patents

Description

  The present invention relates to a coolant cooling circuit that forms a coolant circulation path for cooling, for example, electronic equipment or cooling in a heat insulating housing.

Conventionally, for example, a refrigerant cooling circuit is used to cool an electronic device having a large calorific value, or to cool the interior of a vending machine, a refrigerator, an air conditioner or the like. The refrigerant cooling circuit forms a refrigerant circulation path (refrigeration cycle) that circulates the refrigerant mainly through the compressor, radiator, constrictor, and evaporator, and uses the latent heat of vaporization by the evaporator to heat the evaporator and heat. Connect to cool electronic equipment, or attach a fan to the evaporator and circulate the air in the refrigerator to cool.
The heat transfer coefficient between the evaporating refrigerant and the evaporator tube wall in the evaporator is related to the gas-liquid ratio (hereinafter referred to as the void ratio) of the refrigerant as shown in FIG. This example qualitatively shows the change in the heat transfer mode in the case where uniform heating is applied to an evaporation pipe with a vertical pipe line and liquid is supplied from the lower end. The heat transfer coefficient is low when the void ratio is 0 at the lower end and the liquid is in a liquid single-phase flow in which the refrigerant is completely in a liquid state. It increases linearly up to about 0.3. And when the void ratio is about 0.3 to 0.7, the heat transfer coefficient is constant, and when the void ratio exceeds about 0.7, it further increases when it becomes an annular spray flow from the bubble flow, and finally It will be highest just before the dryout when it becomes completely gaseous. (For example, refer nonpatent literature 1).
On the other hand, as a refrigerant cooling circuit that efficiently uses a refrigeration cycle, for example, in the refrigerant control of an air conditioner that uses carbon dioxide as a refrigerant, the superheat degree of the evaporator becomes a constant value (for example, 5 ° C.). A circuit that controls the opening degree of the expansion valve and controls the temperature and pressure on the high-pressure side to have predetermined values using a refrigerant amount adjusting means is known. (For example, refer to Patent Document 1).
Issued by Yasuhiro Ueda “Gas-liquid two-phase flow” September 20, 1981 JP 2006-153349 A

However, controlling the degree of superheat of the evaporator at a constant level means that the downstream part of the evaporator will be in a gas phase, so it will be used in a dryout state as described above, and the evaporator will be used efficiently. This is disadvantageous in that it requires the use of an evaporator that is larger than necessary.
Therefore, the present invention has been considered in view of the above points, and it is possible to efficiently use the evaporator, and thus, the size of the evaporator that can effectively use the equipment in which the evaporator is mounted and the space in the refrigerator. An object of the present invention is to provide a refrigerant cooling circuit that achieves the above.

In order to achieve the above object, a refrigerant cooling circuit according to a first aspect of the present invention includes a compressor that compresses a refrigerant, a radiator that dissipates heat from the refrigerant that is supplied from the compressor, and a radiator that is supplied from the radiator. A refrigerant cooling circuit having a refrigerant circulation path having a throttle part for adjusting a flow rate of the refrigerant and an evaporator for evaporating the refrigerant supplied from the throttle part and returning the refrigerant to the compressor;
Gas-liquid detection means for detecting the gas-liquid ratio of the refrigerant flowing upstream and downstream of the evaporator is provided, and the flow rate of the refrigerant is determined by the opening of the throttle unit according to the gas-liquid ratio detected by the gas-liquid detection means. It is characterized by controlling.
A refrigerant cooling circuit according to a second aspect of the invention includes a compressor that compresses the refrigerant, a radiator that dissipates the refrigerant supplied from the compressor, and a throttle unit that adjusts the flow rate of the refrigerant supplied from the radiator. And a refrigerant cooling circuit that forms a refrigerant circulation path with an evaporator that evaporates the refrigerant supplied from the throttle and returns it to the compressor.
Gas-liquid detection means for detecting the gas-liquid ratio of the refrigerant flowing upstream and downstream of the evaporator is provided, and the flow rate of the refrigerant is determined by the rotation speed of the compressor according to the gas-liquid ratio detected by the gas-liquid detection means. It is characterized by controlling.
A refrigerant cooling circuit according to a third aspect of the present invention is the refrigerant cooling circuit according to the first or second aspect, wherein the refrigerant is carbon dioxide.

According to the refrigerant cooling circuit of the present invention, the compressor for compressing the refrigerant, the radiator for radiating the refrigerant supplied from the compressor, and the flow rate of the refrigerant supplied from the radiator are adjusted. Refrigerant flowing in the upstream and downstream sides of the evaporator in a refrigerant cooling circuit that forms a refrigerant circulation path having a throttle section that performs and an evaporator that evaporates the refrigerant supplied from the throttle section and returns it to the compressor The gas-liquid detection means for detecting the gas-liquid ratio is provided, and the flow rate of the refrigerant is controlled by the opening of the throttle portion according to the gas-liquid ratio detected by the gas-liquid detection means. Since heat is exchanged with the evaporator wall without drying out, the heat exchange rate of the evaporator can be increased while maintaining a high heat transfer rate. As a result, the evaporator can be reduced in size.
According to the refrigerant cooling circuit of the present invention, the compressor for compressing the refrigerant, the radiator for radiating the refrigerant supplied from the compressor, and the flow rate of the refrigerant supplied from the radiator are adjusted. Refrigerant flowing in the upstream and downstream sides of the evaporator in a refrigerant cooling circuit that forms a refrigerant circulation path having a throttle section that performs and an evaporator that evaporates the refrigerant supplied from the throttle section and returns it to the compressor The gas-liquid detection means for detecting the gas-liquid ratio is provided, and the flow rate of the refrigerant is controlled by changing the rotation speed (compression ratio) of the compressor according to the gas-liquid ratio detected by the gas-liquid detection means. As a result, since the refrigerant can be operated while maintaining a high heat transfer rate without drying out, the evaporator can be downsized. Furthermore, since the flow rate of the refrigerant is controlled by the rotation speed of the compressor, the controllability is improved.

  According to the vending machine according to the third aspect of the present invention, since the refrigerant uses carbon dioxide, it can be cooled without increasing the global warming potential. Therefore, it is possible to provide a highly safe refrigerant cooling circuit.

(Embodiment 1)
Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. The present invention is not limited to the first embodiment.
FIGS. 1-6 is the figure explaining Embodiment 1 which concerns on this invention of Claim 1. FIG. 1 is a circuit diagram of a cooling refrigerant circuit according to Embodiment 1. FIG. 2 is an explanatory diagram of an optical sensor that is the gas-liquid detection means shown in FIG. 1, and FIG. 3 (a) is an explanatory diagram of an optical sensor arranged upstream of the evaporator. (B) is explanatory drawing of the optical sensor arrange | positioned in the downstream part of the evaporator. FIG. 4 is a block diagram of control means relating to the first embodiment. FIG. 5 is an explanatory diagram showing the results of measuring the heat transfer coefficient of the evaporator according to the first embodiment. FIG. 6 is a flowchart of control relating to the first embodiment.
As shown in FIG. 1, the refrigerant cooling circuit in the first embodiment mainly includes a two-stage compression compressor 1, a gas cooler (heat radiator) 2, an electronic expansion valve (throttle portion) 3, and an evaporator 4. 6 to form a refrigeration cycle in which refrigerant can be circulated. An intermediate heat exchanger 10 that dissipates heat of the intermediate pressure refrigerant discharged from the two-stage compression compressor 1 and an oil separator 11 that returns the refrigeration oil to the compressor 1 are connected to the compressor 1. Furthermore, optical sensors 51 and 52 as gas-liquid detection means for detecting the gas-liquid ratio of the refrigerant are connected to the upstream side and the downstream side of the evaporator 4, and the electronic expansion valve 3, A control device 70 for controlling the compressor 1 and the like is provided. In the first embodiment, the refrigerant is carbon dioxide that has non-flammability, safety, and non-corrosion properties, and has little influence on the ozone layer.

More specifically, the compressor 1 compresses the carbon dioxide returned from the evaporator 4 to a high temperature and high pressure state, and performs a two-stage compression operation using the intermediate heat exchanger 10. To do. Specifically, in the two-stage compression operation, the compressor 1 has an intermediate heat between the first compressor 1a that performs the first-stage compression operation and the second compressor 1b that performs the second-stage compression operation. An exchanger 10 is provided. Then, after the first stage compression operation by the first compressor 1a, the intermediate heat exchanger 10 cools the carbon dioxide compressed by the first compressor 1a and returns it to the second compressor 1b. In this way, the compressor 1 performs a two-stage compression operation via the intermediate heat exchanger 10, thereby obtaining high compression efficiency with low power consumption and compressing carbon dioxide to a desired high temperature and high pressure state. It becomes possible to do. The compressor 1 is driven by an inverter (not shown), and can control the refrigerant circulation amount, the high-pressure side pressure, and the like by changing the rotation speed.
The gas cooler 2 is for radiating the high-temperature and high-pressure carbon dioxide supplied from the compressor 1 to cool the carbon dioxide. As the gas cooler 2 in this embodiment, for example, a fin tube type composed of a copper tube and an aluminum fin is used. The gas cooler 2 is provided with a fan 21, and the fan 21 is for blowing the gas cooler 2.

The electronic expansion valve 3 is for reducing the pressure of carbon dioxide supplied from the gas cooler 2 and controlling the evaporation temperature and flow rate. The electronic expansion valve 3 is directly connected to a pulse motor (not shown), and the opening degree of the expansion valve is changed by controlling the rotation angle of the pulse motor by the control device 70.
The evaporator 4 is for cooling the ambient temperature using latent heat obtained by evaporating the liquid phase carbon dioxide supplied from the electronic expansion valve 3. The evaporator 4 in the present embodiment uses a fin tube type composed of, for example, a copper tube and an aluminum fin.
The evaporator 4 is connected to a cooling load (not shown). For example, in the case of an electronic device, the evaporator 4 is thermally connected to a heating element such as an IGBT. If it is a vending machine, a refrigerator, a refrigerated showcase / refrigerated showcase, a beverage dispenser, etc., the evaporator 4 is disposed with a fan inside the cooler of the heat insulating casing, and cools the interior with circulating air.
The intermediate heat exchanger 10 is for cooling the intermediate-pressure refrigerant compressed by the first compressor 1a and returning it to the second compressor 1b. The intermediate heat exchanger 10 is constituted by, for example, a so-called fin-and-tube type condenser in which a copper tube passes through an aluminum fin that is an aluminum plate, and is provided side by side with the gas cooler 2.

The oil separator 11 is for returning the refrigeration oil discharged from the compressor 1 to the compressor 1. The refrigerating machine oil prevents friction and refrigerant leakage in the compressor 1, but it is difficult to completely seal the refrigerating machine oil inside the compressor 1. In particular, as described above, the compressor 1 compresses carbon dioxide to a high pressure, and this pressure is much higher than when, for example, an HFC refrigerant (hydrofluorocarbon) is used. The discharge amount of machine oil increases. Therefore, in the first embodiment, in the compressor 1, the oil separator 11 is connected between the outlet side of the second compressor 1b and the inlet side of the first compressor 1a, and the second compressor 1b. The refrigerating machine oil discharged from is returned to the first compressor 1a.
The internal heat exchanger 14 is for exchanging heat between the high pressure side and the low pressure side of the refrigerant circulation path. The high pressure side of the refrigerant circulation path is from the outlet side of the compressor 1 through the gas cooler 2 to the inlet side of the electronic expansion valve 3. The low pressure side of the refrigerant circulation path is from the outlet side of the electronic expansion valve 3 to the inlet side of the compressor 1 through the evaporator 4.
The fan 21 is for exhausting heat from the compressor 1, the gas cooler 2, and the intermediate heat exchanger 10. The fan 21 is disposed between the gas cooler 2 and the compressor 1, and blows air to the intermediate heat exchanger 10 and the gas cooler 2 in a mode of sucking and pushes the compressor 1. To blow air.

The optical sensor 51 is disposed between the electronic expansion valve 3 and the evaporator 4 and detects the void ratio of the refrigerant on the upstream side of the evaporator 4. As shown in FIG. 2, the optical sensor 51 includes a light projecting unit 51 a and a light receiving unit 51 b, and is installed at opposed positions via detection windows 51 c and 51 c installed on the upper and lower surfaces of the pipe 6. Yes. The light projecting unit 51a is for projecting light, and the light receiving unit 51b receives the light projected from the light projecting unit 51a, detects the amount of light, converts it into a signal, and controls the control device. 70.
The detection windows 51c and 51c are formed of sight glass at the center, and are installed on the upper and lower surfaces of the pipe 6 in a manner that matches the temperature and pressure of the refrigerant.
The optical sensor 52 is disposed on the downstream side of the electronic expansion valve 3 and detects the void ratio of the refrigerant on the downstream side of the evaporator 4. Similarly to the above, the optical sensor 52 has the light receiving unit 52b, and is installed at a facing position via detection windows 52c and 52c installed on the upper and lower surfaces of the pipe 6.
As shown in FIG. 3, the optical sensors 51 and 52 measure the amount of light that has passed through the gas-liquid two-phase refrigerant. The light that passes through the refrigerant has a high absorption rate when the refrigerant is in a liquid phase state and a low absorption rate when the refrigerant is in a gas phase state. Therefore, by measuring the amount of light at the light receiving unit 51b, The gas-liquid ratio (void ratio) can be detected.

In addition, although the optical sensors 51 and 52 were used as a gas-liquid detection means which detects a void rate, the same effect can be acquired even if it uses an ultrasonic sensor.
As shown in FIG. 4, the control device 70 includes a main control unit 71, a memory 72, and the like, detects the void ratio of the refrigerant from the optical sensors 51, 52, and the electronic expansion valve 3, the compressor 1, etc. Is to control.
The inventors manufactured an experimental circuit equivalent to the circuit shown in FIG. 1, connected a simulated load (specifically, a heater that generates a certain amount of heat) to the evaporator 4, and further used a mass flow rate for measurement. The heat transfer coefficient of the evaporator 4 was measured by connecting a meter, a precooler, and a sight glass. The mass flow rate (mass velocity) of the circulating refrigerant is controlled to be constant according to the rotation speed by the inverter of the compressor 1 and the opening of the electronic expansion valve 3, and the refrigerant temperature of the evaporator 4 is changed by the precooler. Void rate and heat transfer rate were measured. The heat transfer coefficient was calculated from the difference between the surface temperature of the evaporator 4 and the refrigerant temperature and the heating amount of the simulated load.
The result is shown in FIG. The void fraction on the downstream side of the evaporator 4 is shown in parentheses in the figure. As can be seen from the figure, the heat transfer rate decreases drastically in the dryout state where the void rate is 1 even when the mass velocities are different. Therefore, it is evaporated by maintaining the void rate in the vicinity of 1 and operating. The unit can be operated with a high heat transfer coefficient.

In the experiment, the gas-liquid state of the refrigerant was observed with a sight glass. The annular spray flow in the case of the vertical pipe shown in FIG. 8 has a liquid phase on the wall surface, but since the experiment uses a horizontal pipe, rather it is shown in FIGS. 3 (a) and 3 (b). It was confirmed visually that the upper part was separated into the gas phase and the lower part into the liquid phase.
In such a configuration, when the compressor 1 is operated, the refrigerant compressed by the first compressor 1a of the two-stage compressor 1 is radiated once by the intermediate heat exchanger 10 as shown in FIG. The second compressor 1b is compressed to a high pressure. The compressed refrigerant is radiated by the gas cooler 2 through the oil separator 11, performs heat exchange in the internal heat exchanger 14, and flows into the electronic expansion valve 3. The electronic expansion valve 3 is expanded to a low temperature and a low pressure, becomes a gas-liquid two-phase, and flows into the evaporator 4 through the optical sensor 51. The refrigerant evaporates in the evaporator 4 and returns to the inlet of the first compressor 1 a of the two-stage compressor 1 through the optical sensor 52 and the low-pressure side pipe of the internal heat exchanger 14.
On the other hand, in the oil separator 11, only the refrigeration oil in the refrigerant is separated and returned to the inlet of the two-stage compressor 1.
Next, a control method will be described using the flowchart of FIG. The control device 70 confirms whether the compressor is operating (S1), and returns to the standby state if it is not operating (S1 branch N). If it is operating, the void ratio of the refrigerant on the upstream side of the evaporator 4 is read from the sensor 51 (S2).

If the void ratio of the upstream refrigerant is 0.5 or more, it is determined that the refrigerant is excessively throttled and the opening of the electronic expansion valve is increased (S4). If the void ratio is 0.5 or less, next, the void ratio of the refrigerant on the downstream side of the evaporator 4 is read from the sensor 52 (S5).
If the void ratio of the downstream refrigerant is 0.95 or more (S6 branch Y), it is determined that the refrigerant is insufficiently throttled and the opening of the electronic expansion valve 3 is reduced (S7). If the void ratio is 0.95 or less, the control is returned to the beginning and the same control is repeated, and the void ratio from the inlet portion to the outlet portion in the evaporator is appropriately maintained.
Thus, it can be seen that the evaporator can be operated with a high heat transfer rate by controlling the flow rate of the refrigerant so that the void rate is slightly lower than 1.
(Embodiment 2)
Next, a second embodiment according to the invention of claim 2 will be described with reference to a flowchart shown in FIG. The difference between the second embodiment and the first embodiment is that control is performed by changing the rotation speed of the compressor instead of controlling the electronic expansion valve 3 by the void ratio. Other configurations are substantially the same as those of the first embodiment, and thus description thereof is omitted.
As shown in FIG. 7, the control device 70 confirms whether the compressor 1 is operating (S1), and returns to the standby state if not operating (S1 branch N). If it is operating, the void ratio of the refrigerant on the upstream side of the evaporator 4 is read from the sensor 51 (S2).

If the void ratio of the upstream refrigerant is 0.5 or more, it is determined that the refrigerant is excessively throttled and the rotation speed of the compressor 1 is increased (S4a). If it is 0.5 or less, the void ratio of the refrigerant on the downstream side of the evaporator 4 is read from the sensor 52 (S5).
If the void ratio of the downstream refrigerant is 0.95 or more (S6 branch Y), it is determined that the refrigerant is insufficiently throttled and the rotational speed of the compressor 1 is reduced (S7a). If it is 0.95 or less, the control is returned to the beginning and the same control is repeated, and the void ratio from the inlet portion to the outlet portion in the evaporator is appropriately maintained.
In such a cooling refrigerant circuit, the same effects as those of the first embodiment can be obtained, and the mass flow rate of the refrigerant can be increased in proportion to the rotation speed of the compressor as compared with the electronic expansion valve 3. Therefore, there is an effect that the controllability becomes easy.
Moreover, if the electronic expansion valve 3 and the rotation speed of the compressor 1 are combined and controlled, the flow rate of the refrigerant can be easily controlled more finely.
In addition, the use of carbon dioxide as a refrigerant reduces the impact on global warming, unlike chlorofluorocarbon refrigerants, and has the effect of operating the cooling device safely because it is less flammable than HC refrigerants. .

  As described above, the cooling refrigerant circuit according to the present invention is useful for cooling an electronic device or cooling a heat-insulating housing by using latent heat of an evaporator of a refrigeration cycle.

1 is a circuit diagram of a cooling refrigerant circuit according to Embodiment 1. FIG. Explanatory drawing of the optical sensor part shown in FIG. It is explanatory drawing of the optical sensor part shown in FIG. 1, (a) is a sensor arrange | positioned in the upstream part of an evaporator, (b) is explanatory drawing of the optical sensor arrange | positioned in the downstream part of an evaporator. FIG. 3 is a block diagram of control means relating to the first embodiment. Explanatory drawing which shows the result of having measured the heat transfer rate regarding Embodiment 1. FIG. 5 is a flowchart of control related to the first embodiment. 10 is a flowchart of control related to the second embodiment. Explanatory drawing which shows the change of a heat transfer mode about the flow of the refrigerant | coolant in an evaporation pipe.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Compressor 1a 1st compressor 1b 2nd compressor 2 Gas cooler (heat radiator)
3 Electronic expansion valve (throttle part)
4 Evaporator 10 Intermediate Heat Exchanger 11 Oil Separator 14 Internal Heat Exchanger 21 Fan 51, 52 Light Sensor 51a, 52a Light Emitting Part 51b, 52b Light Receiving Part 51c, 52c Detection Window 70 Control Device

Claims (3)

A compressor that compresses the refrigerant; a radiator that dissipates the refrigerant supplied from the compressor; a throttle that adjusts a flow rate of the refrigerant supplied from the radiator; and a refrigerant supplied from the throttle In a refrigerant cooling circuit that forms a refrigerant circulation path with an evaporator to be returned to the compressor,
Gas-liquid detection means for detecting the gas-liquid ratio of the refrigerant flowing upstream and downstream of the evaporator is provided, and the flow rate of the refrigerant is determined by the opening of the throttle unit according to the gas-liquid ratio detected by the gas-liquid detection means. The refrigerant cooling circuit characterized by controlling. A compressor that compresses the refrigerant; a radiator that dissipates the refrigerant supplied from the compressor; a throttle that adjusts a flow rate of the refrigerant supplied from the radiator; and a refrigerant supplied from the throttle In a refrigerant cooling circuit that forms a refrigerant circulation path with an evaporator to be returned to the compressor,
Gas-liquid detection means for detecting the gas-liquid ratio of the refrigerant flowing upstream and downstream of the evaporator is provided, and the flow rate of the refrigerant is determined by the rotation speed of the compressor according to the gas-liquid ratio detected by the gas-liquid detection means. The refrigerant cooling circuit characterized by controlling. The refrigerant cooling circuit according to claim 1 or 2, wherein the refrigerant is carbon dioxide.

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