JP2000088371A - Heat pump device using non-azeotrope refrigerant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve heat exchanging capacity of a non-azeotrope refrigerant in a low temperature side evaporating step by changing a concentration ratio of the refrigerant in the low temperature side evaporating step and a high temperature side evaporating step to become a value near an optimum in each step, thereby suppressing generation of an excess operating pressure in the high temperature step. SOLUTION: A gas-liquid separator 5 for separating a gas-liquid two phase flow supplied from an evaporator 1 to a gas phase and a liquid phase and a sub-expansion valve 8 for evaporating the liquid phase flow from the separator 5 to supply it to a compressor 4 and heat exchangers 10, 9 are connected to a refrigerant circulating passage 21 between the evaporator 1 and the compressor 4. A gas-liquid mixer 6 for mixing a gas phase flow supplied from the separator 5 via a refrigerant bypass passage 13 with a liquid phase flow from the compressor 4 to supply the mixture to the evaporator 1 is connected to a refrigerant circulating passage 22 between the compressor 4 and the evaporator 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat pump device such as a refrigerating device or a heat pump which constitutes a heat cycle for transferring heat between a low-temperature side heat source and a high-temperature side heat source. The present invention relates to a heat pump device using an azeotropic mixed refrigerant.

[0002]

2. Description of the Related Art As shown in FIG. 5, a vapor compression type refrigeration system comprises an evaporator (1), a compressor (4), a condenser (3) and an expansion valve.
(2) are connected to each other by piping to realize a refrigeration cycle as shown in FIG. That is, the evaporator
Refrigerant gas from (1) is compressed by compressor (4) (→)
Then, the refrigerant gas becomes a high-temperature, high-pressure gas, and the refrigerant gas discharged from the compressor (4) is sent to the condenser (3), where a high-temperature heat source (outside air)
Condenses (→) by releasing heat to The high-temperature, high-pressure refrigerant liquid liquefied by condensation is supplied to the expansion valve (2), and becomes a low-temperature, low-pressure refrigerant liquid by expansion (→). The refrigerant liquid from the expansion valve (2) is sent to the evaporator (1), deprives the heat from the low-temperature heat source (freezing room) and evaporates (→),
The refrigerant gas is supplied to the compressor (4). By repeating the above refrigeration cycle (→→→→), heat is transferred from the low-temperature heat source to the high-temperature heat source, and the low-temperature heat source is cooled.

[0003] As a refrigerant, generally, CFC, HCFC,
Freon (trade name of DuPont) such as HFC has been adopted, and further adoption of a natural refrigerant such as carbon dioxide and ammonia has been studied. Also, to obtain an appropriate saturation pressure for the set heat source temperature, the density, viscosity, thermal conductivity, specific heat,
Refrigeration that uses a mixed refrigerant made by mixing two types of refrigerants for the purpose of improving thermal or dynamic characteristics such as latent heat, reducing the flammability and toxicity of the refrigerant, and improving safety. Equipment is being developed. In such a refrigerating apparatus, it is necessary to select the combination and concentration ratio (composition ratio) of the two types of refrigerants to be mixed in order to obtain the best performance as a whole heat cycle.

[0004]

Generally, a heat cycle of a refrigeration system includes a plurality of processes having different temperature ranges and conditions, and a desired concentration ratio exists for each process. However, in a conventional refrigeration system using a mixed refrigerant, the mixed refrigerant mixed at a specific concentration ratio circulates through the entire heat cycle at a constant concentration ratio.
Optimal concentration ratios cannot be achieved for all processes. For example, as a result of reducing the operating pressure in the high-temperature side condensation process, the heat exchange capacity in the low-temperature side evaporation process may be impaired. Further, when the temperature difference between the heat sources is large, there is a problem that the loss in the compression process increases due to an increase in the pressure ratio. Further, it is difficult to obtain good refrigerant characteristics at both operating temperatures in the low-temperature side evaporation process and the high-temperature side condensation process.

The numerical values in FIG. 5 exemplify a state change in a vapor compression refrigeration system using a mixed refrigerant (non-azeotropic mixed refrigerant) of carbon dioxide (50%) and isobutane (50%). Carbon dioxide has a higher heat exchange rate and lower viscosity than other natural refrigerants in the low temperature range, especially in the freezing temperature range, and exhibits extremely excellent heat exchange capacity, but because of its low critical temperature,
When a thermal cycle is formed by itself, there is a disadvantage that the operating pressure is increased. In contrast, isobutane has a lower saturation pressure than carbon dioxide, and the working pressure can be reduced by mixing isobutane with carbon dioxide. However, in a heat cycle in which a mixed refrigerant of carbon dioxide and isobutane is circulated throughout the entire heat cycle at a constant concentration ratio, as shown in FIG. 5, for example, as shown in FIG. When the concentration ratio is set to 50%, the operating pressure is 50% in the high temperature side condensation process because the concentration ratio of carbon dioxide is as high as 50%.
There is a problem that reaches bar.

Accordingly, an object of the present invention is to provide a heat pump apparatus using a non-azeotropic mixed refrigerant, wherein the concentration ratio of the mixed refrigerant in the low-temperature side evaporation process and the high-temperature side condensation process becomes an optimum or nearly optimum value in each process. Thus, the generation of excessive operating pressure in the high-temperature side condensation process is suppressed, and the heat exchange capacity of the mixed refrigerant in the low-temperature side evaporation process is improved.

[0007]

In the non-azeotropic refrigerant mixture, the saturation line and the vapor line change depending on the temperature, but at the same time, these boundary lines also change depending on the concentration ratio. For example, when it is desired to reduce the operating pressure in the high-temperature side condensation process, the concentration ratio (composition ratio) of the refrigerant having a low saturation pressure (for example, isobutane) may be increased. Further, in order to increase the heat exchange capacity of the refrigerant in the low temperature side evaporation process, the concentration ratio (composition ratio) of the refrigerant having a high saturation pressure (for example, carbon dioxide) may be increased.

Therefore, in the heat pump device according to the present invention, the refrigerant circulation path for flowing the refrigerant from the evaporator (1) to the compressor (4) so as to change the concentration ratio of the mixed refrigerant in both the condensation and evaporation processes. Then, a gas-liquid separator (5) for separating the gas-liquid two-phase flow supplied from the evaporator (1) into a gas phase and a liquid phase, and the liquid phase flow from the gas-liquid separator (5) is vaporized. Evaporation means for supplying to the compressor (4) is connected. Also, evaporator from compressor (4)
In the refrigerant circulation path for flowing the refrigerant to (1), a vapor phase flow supplied from the gas-liquid separator (5) via the refrigerant bypass path and a liquid phase flow from the compressor (4) are mixed to form an evaporator. A gas-liquid mixer (6) for supplying to (1) is connected.

In the heat pump device of the present invention, the gas-liquid two-phase flow flows out of the evaporator (1), and the gas-liquid separator
(5). In the gas-liquid separator (5), the gas-liquid two-phase flow is separated into a gas phase and a liquid phase, and the liquid phase flow is supplied to the vaporizing means, while the gas phase flow is supplied to the gas-liquid mixer (6). You. here,
The liquid phase flow has a high concentration ratio of the refrigerant having a low saturation pressure (isobutane), whereas the gas phase flow has
The refrigerant (carbon dioxide) having a high saturation pressure has a high concentration ratio. Therefore, a vapor phase stream having a high concentration ratio of the refrigerant (isobutane) having a low saturation pressure is obtained from the vaporizing means, and the vapor phase stream is supplied to the condenser (3), and the high-temperature side condensation is performed. The working pressure of the process will be reduced.

The gaseous phase flow from the gas-liquid separator (5) has a high concentration ratio of refrigerant (carbon dioxide) having a high saturation pressure, and the gaseous phase stream is condensed by the condenser (3). Refrigerant that has a higher saturation pressure than the
A gas-liquid two-phase flow with a higher concentration ratio of (carbon dioxide)
It is supplied to the evaporator (1). As a result, a gas-liquid two-phase mixed refrigerant consisting of a gas phase and a liquid phase flows out of the evaporator (1). That is, in the high temperature side condensation process, the concentration ratio (composition ratio) of the refrigerant (isobutane) having a low saturation pressure increases, and the operating pressure decreases. In the low-temperature side evaporation process, the concentration ratio (composition ratio) of the refrigerant (carbon dioxide) having a high saturation pressure increases, the operating pressure increases, and the thermal and dynamic characteristics of the mixed refrigerant are improved.

In a specific configuration, the vaporizing means includes a sub-expansion valve (8) for expanding the liquid-phase flow from the gas-liquid separator (5), and a refrigerant that flows out of the sub-expansion valve (8) for vaporization. Heat exchanger. According to this specific configuration, the liquid phase flow from the gas-liquid separator (5) can be completely vaporized and supplied to the compressor (4).

A second gas-liquid separator is connected to the outlet of the vaporizing means, and the gas-phase flow from the gas-liquid separator is supplied to the compressor (4), while the gas-liquid separator is connected to the second gas-liquid separator. Is supplied to the gas-liquid mixer (6) via the second refrigerant bypass. According to the specific configuration, even if the refrigerant from the gas-liquid separator (5) may not be completely vaporized, the refrigerant may
Is separated into a gas phase and a liquid phase, and only the gas phase stream is supplied to the compressor (4). The liquid phase flow is a gas-liquid mixer
Is supplied to (6).

In a further specific configuration, the gas-liquid separator (5)
There is a sub-compressor in the refrigerant bypass between
(7) is connected. According to this specific configuration, the gas-phase flow from the gas-liquid separator (5) is boosted to a pressure equivalent to the liquid-phase flow from the condenser (3) and supplied to the gas-liquid mixer (6). And
When mixed with the liquid phase flow from the condenser (3), the concentration ratio (composition ratio) of the refrigerant (carbon dioxide) having a high saturation pressure increases.

In a more specific configuration, a heat exchanger for removing heat from the refrigerant flowing through the refrigerant bypass is connected to the refrigerant bypass between the sub-compressor (7) and the gas-liquid mixer (6). Have been. According to the specific configuration, the heat taken out by the heat exchange is supplied to the high-temperature side heat source, so that the heat can be effectively used.

[0015]

According to the heat pump apparatus using a non-azeotropic mixed refrigerant according to the present invention, the concentration ratio of the non-azeotropic mixed refrigerant in the high-temperature side condensation process and the low-temperature side evaporation process is set to an optimum or near optimum value, respectively. By suppressing the generation of excessive operating pressure in the high-temperature side condensation process, the heat exchange capacity of the mixed refrigerant in the low-temperature side evaporation process can be improved.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment in which the present invention is applied to a vapor compression type refrigeration apparatus will be specifically described with reference to the drawings. The refrigeration apparatus of the present invention shown in FIG. 1 employs a non-azeotropic mixed refrigerant obtained by mixing carbon dioxide and isobutane as a refrigerant.
At the same time as lowering the operating pressure by setting it as low as about 0%, in the low temperature expansion process, the carbon dioxide concentration ratio is set as high as about 50% to realize excellent heat exchange capacity. The heat cycle realized by the refrigeration system is 80
It supplies heat to a high-temperature heat source of 50 ° C. to 50 ° C., and at the same time, removes heat from a low-temperature heat source of 0 ° C. to generate cold heat. It has both functions of a refrigerating device and a heat pump, and has an operating pressure of 30 bar or less. It is suppressed to.

The refrigerating apparatus includes an evaporator (1) in which heat exchange with a low-temperature side heat source causes the refrigerant to evaporate and absorb at about 0 ° C.
Immediately before that, an expansion valve (2) that expands the mixed refrigerant, a condenser (3) in which heat exchange with the high-temperature side heat source causes condensation and heat dissipation of the refrigerant at around 80 ° C to 50 ° C, and compression and compression of the refrigerant immediately before that. And a compressor (4) for compression. Then, in order to change the concentration ratio of the mixed refrigerant between the evaporation and compression temperatures, the refrigerant circulation path (2) between the evaporator (1) and the compressor (4) is changed.
In 1), the concentration ratio of the gas-liquid two-phase flow supplied from the evaporator (1)
A composition adjusting expansion valve (11) for adjusting (composition ratio), and a gas-liquid separator (5) for separating a gas-liquid two-phase flow from the composition adjusting expansion valve (11) into a gas phase and a liquid phase And are connected. Also, condenser
An internal heat exchanger (10) and a gas-liquid mixer (6) are connected to a refrigerant circuit (22) between (3) and the evaporator (1). The liquid phase flow from the gas-liquid separator (5) is supplied to the sub-expansion valve (8), internal heat exchanger.
It is supplied to the compressor (4) via (10) and the intermediate heat exchanger (9). On the other hand, the gas-phase flow from the gas-liquid separator (5) is guided to the refrigerant bypass passage (13) and passes through the sub-compressor (7) to the gas-liquid mixer.
Is supplied to (6).

FIG. 1 exemplifies the states S1 to S11 (temperature, pressure, carbon dioxide concentration ratio, phase state) of the mixed refrigerant flowing at each point in the refrigeration apparatus. FIG. 4 (a)
(b) and (c) show the mass ratio (concentration ratio) and pressure of carbon dioxide at each point (states S1 to S11) in the vapor-liquid equilibrium diagram. In FIG. 4, (L) is a liquid state,
(L + G) indicates a gas-liquid two-phase state, and (G) indicates a gas-phase state.

FIG. 4A shows an evaporator (1) and a gas-liquid separator (5).
Represents the change in the state of the refrigerant at the time of. Inside the evaporator
In (state S1), the carbon dioxide concentration ratio of the mixed refrigerant (hereinafter, referred to as
50%, temperature 0 ° C, pressure 17
bar, and in this state, the refrigerant is in a liquid phase state. The refrigerant having a 50% concentration ratio evaporates in the evaporator (1) and removes heat from the low-temperature heat source. However, the refrigerant does not completely become a vapor but as a liquid-gas two-phase flow via the expansion valve (11) for adjusting the composition. Gas-liquid separator (5)
Flows into. Here, the refrigerant flows from 17 bar to 15 b due to the pressure loss in the evaporator (1) and the composition adjusting expansion valve (11).
ar (state S2), and since the liquid is a non-azeotropic mixture, the temperature also changes from 0 ° C. to 10 ° C. As a result, the mixed refrigerant is separated into a liquid phase (state S3) having a concentration ratio of 20% and a gas phase (state S9) having a concentration ratio of 70% in the gas-liquid separator (5).

The liquid phase flow having a concentration ratio of 20% (state S3) further passes through the sub-expansion valve (8) and the internal heat exchanger (10), is expanded and heated to reach the state S4, and a part thereof is evaporated. It becomes a gas-liquid two phase.
The gas-liquid two-phase flow having a concentration ratio of 20% is further supplied to an intermediate heat exchanger (9).
And finally receives a heat from a medium temperature heat source at 40 ° C., and finally enters a complete gas phase state (state S5) with a concentration ratio of 20%, a temperature of 40 ° C. and a pressure of 5 bar, and the compressor (4) ).

FIG. 4B shows the compression and condensation processes of the refrigerant. The mixed refrigerant having a concentration ratio of 20% is compressed from 5 bar to 25 bar by the compressor (4), and its temperature is 4 bar.
The temperature changes from 0 ° C. to a high temperature of 80 ° C. (state S6). Compressor
The gas-phase mixed refrigerant flowing out of (4) radiates heat to a high-temperature heat source in the condenser (3), and at the same time its temperature drops to about 40 ° C. As described above, since the non-azeotropic refrigerant mixture is used as the refrigerant, a temperature change of the refrigerant occurs even in the condensation process, and the heat medium from the high-temperature heat source flows in a direction opposite to the flow of the mixed refrigerant. Thereby, good heat exchange is realized. In this example, the refrigerant having a concentration ratio of 20% is completely condensed into a liquid phase (state S7) in the condenser. The high-pressure liquid phase flow (state S7) from the condenser (3) flows in the internal heat exchanger (10) in the opposite direction to the flow in the low-pressure state, is cooled to 20 ° C., and further exchanges the internal heat. Due to the pressure drop in the vessel (10), 20.5
The pressure is reduced to bar (state S8).

Most of the heat of the refrigerant that has absorbed heat through the evaporator (1) is transported by the gas phase (state S9) separated by the gas-liquid separator (5). In order to establish a refrigeration cycle, it is necessary to cool this gas phase flow. As will be described later, this cooling is performed by dissipating heat to a high-temperature heat source in the condenser (3) and further in the internal heat exchanger (10). This is performed by a cooled refrigerant having a concentration ratio of 20% (state S8).

The concentration ratio obtained from the gas-liquid separator (5) is 70%.
The gaseous phase refrigerant in (state S9) is compressed by the sub-compressor (7), and has a temperature of 40 ° C. and a pressure of 20.5 bar (phase S1).
0). On the other hand, the mixed refrigerant having the concentration ratio of 20% in the state S8 is cooled by the internal heat exchanger (10) to have a temperature of 20 ° C., which is lower than the gas phase flow having the 70% concentration ratio in the state S10. Therefore, it is possible to cool the gas phase flow in this state S10. The cooling is performed by mixing the 20% concentration liquid phase flow of the state S8 and the 70% concentration gas phase flow of the state S10 with each other in the gas-liquid mixer (6).
That is, as shown in FIG. 4C, a liquid phase flow having a concentration ratio of 20% in the state S8 and a gaseous phase flow having a concentration ratio of 70% in the state S10 are mixed to form a gas phase having a concentration ratio of 70%. Flow is a gas-liquid mixer
(6) The gas-liquid 2 having a concentration ratio of 50%, which is cooled and absorbed in
It becomes a refrigerant in a phase (state S11) and flows out of the gas-liquid mixer (6). This 50% concentration refrigerant is supplied to the expansion valve
After passing through (2), it becomes a gas-liquid two-phase refrigerant in the state S1, and the evaporator (1)
And the same cycle is repeated.

The refrigeration temperature and the refrigeration load are controlled by the opening degree of the expansion valve (2) and the composition adjusting expansion valve (11) arranged before and after the evaporator (1), the compressor (4) and the sub-compressor. It is controlled by adjusting the rotation speed in (7). Further, the gas-liquid mixer (6) is designed to have a sufficient length necessary for sufficiently mixing the two incoming refrigerants.

In the above-described heat cycle of the refrigerating apparatus,
The carbon dioxide concentration ratio in the high-temperature side condensation process is as low as 20%, and the operating pressure is 25 bar, which is sufficiently lower than the cycle of carbon dioxide alone. Further, since the carbon dioxide concentration ratio in the low-temperature side evaporation process becomes as high as 50%, better low-temperature heat exchange capacity can be obtained than when a refrigerant having a concentration ratio of 20% is circulated by itself.

The refrigeration apparatus shown in FIG. 2 is intended to make more effective use of heat than the above-described heat cycle, and has a low-temperature side heat exchange tube having an evaporator (1) as a heat absorption side heat transfer tube as a low-temperature side heat source. A condenser (12) is installed, and a condenser
A high-temperature heat exchanger (15) with (3) as a heat-radiating heat transfer tube is installed. A first intermediate heat exchanger (16) is provided at the outlet of the auxiliary expansion valve (8).
Are connected, the heat-radiation-side heat transfer tubes of the heat exchanger (16) are connected to the heat-radiation-side heat transfer tubes of the high-temperature-side heat exchanger (15), and both ends of both heat transfer tubes are connected to the cooling water pipe (17). . In addition, a second intermediate heat exchanger (14) is connected to the refrigerant bypass passage (13) between the sub-compressor (7) and the gas-liquid mixer (6). The heat-absorbing-side heat transfer tube of (1) is connected to the heat-absorbing-side heat transfer tube of the high-temperature-side heat exchanger (15), and both ends of both heat transfer tubes are connected to the hot water supply pipe (18).

Therefore, the cooling water flowing through the cooling water pipe (17) is first passed through the first intermediate heat exchanger (16) to a temperature of about 30.degree.
After being cooled to 0 ° C, it is further cooled from about 20 ° C to 10 ° C via the low-temperature side heat exchanger (12). On the other hand, the hot water flowing through the hot water supply pipe (18) is first heated from about 30 ° C. to 40 ° C. through the second intermediate heat exchanger (14), and then further passed through the high temperature side heat exchanger (15) to about 40 ° C. C. to about 70.degree.

In the refrigerating apparatus shown in FIG. 3, an intermediate heat exchanger (19) is connected to outlets of the sub-expansion valve (8) and the sub-compressor (7), and the refrigerant flows out of the sub-expansion valve (8). The gas-liquid two-phase refrigerant is heated by the gas-phase refrigerant flowing out of the sub-compressor (7). The heated refrigerant is further supplied to the auxiliary gas-liquid separator (20), And only the gas phase flow is supplied to the compressor (4), and the liquid phase flow is supplied to the gas-liquid mixer (6) via the second refrigerant bypass passage (23). If the gas-liquid two-phase refrigerant flowing out of the auxiliary expansion valve (8) can be completely vaporized by the intermediate heat exchanger (19), the auxiliary gas-liquid separator (20) is omitted. Can be done.

In any of the refrigeration systems described above, the concentration ratio of the mixed refrigerant in the high-temperature side condensation process and the low-temperature side evaporation process can be intentionally changed, thereby lowering the pressure in the high-temperature side condensation process and lowering the low-temperature side evaporation. Increasing the pressure of the process,
It is possible to lower the compression ratio, thereby reducing the loss of the compressor and increasing the efficiency of the heat cycle. In addition, the thermal and dynamic characteristics of the refrigerant in the high-temperature side condensation process and the low-temperature side evaporation process can be changed to ones suitable for each process, thereby increasing the efficiency of the heat cycle.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a configuration and a state change of a refrigeration apparatus using a non-azeotropic mixed refrigerant according to the present invention.

FIG. 2 is a system diagram showing another example of a heat cycle of the present invention.

FIG. 3 is a system diagram showing still another example of a heat cycle of the present invention.

FIG. 4 is a diagram illustrating a state change of the thermal cycle of FIG. 1 in a vapor-liquid equilibrium diagram of a non-azeotropic mixture of carbon dioxide and isobutane.

FIG. 5 is a system diagram showing a configuration of a conventional refrigeration apparatus.

FIG. 6 is a pressure-enthalpy diagram showing a heat cycle of the refrigeration apparatus.

[Explanation of symbols]

 (1) Evaporator (2) Expansion valve (3) Condenser (4) Compressor (5) Gas-liquid separator (6) Gas-liquid mixer (7) Sub-compressor (8) Sub-expansion valve (9) Intermediate Heat exchanger (10) Internal heat exchanger (11) Composition adjustment expansion valve

Claims (5)

[Claims] An evaporator (1), a compressor (4), a condenser (3), and an expansion valve (2) are connected to each other by a pipe to form a refrigerant circulation path through which a non-azeotropic mixed refrigerant circulates. In the heat pump device, a gas-liquid two-phase flow supplied from the evaporator (1) is separated into a gas phase and a liquid phase in a refrigerant circuit for flowing the refrigerant from the evaporator (1) to the compressor (4). Separator (5) and gas-liquid separator (5)
A vaporizer is connected to a vaporizer that vaporizes the liquid-phase flow from the compressor and supplies the vapor to the compressor (4), and the refrigerant circulation path for flowing the refrigerant from the compressor (4) to the evaporator (1) has a gas-liquid separator ( A gas-liquid mixer (6) for mixing the gas-phase flow supplied from 5) through the refrigerant bypass and the liquid-phase flow from the compressor (4) and supplying the mixture to the evaporator (1) is connected. A heat pump device using a non-azeotropic mixed refrigerant characterized by the above-mentioned. The vaporizing means includes a sub-expansion valve (8) for expanding the liquid phase flow from the gas-liquid separator (5), and a heat exchange for heating and vaporizing the refrigerant flowing out of the sub-expansion valve (8). The heat pump device according to claim 1, comprising a heat exchanger. 3. A second gas-liquid separator is connected to an outlet of the vaporizing means, and a gas-phase flow from the gas-liquid separator is supplied to a compressor (4), and a second gas-liquid separator is supplied from the gas-liquid separator. 2. The liquid phase flow of claim 1 is supplied to a gas-liquid mixer (6) via a second refrigerant bypass.
Or the heat pump device according to claim 2. 4. The sub-compressor (7) is connected to a refrigerant bypass between the gas-liquid separator (5) and the gas-liquid mixer (6). A heat pump device according to item 1. 5. A refrigerant bypass between the sub-compressor (7) and the gas-liquid mixer (6) is connected to a heat exchanger for removing heat from the refrigerant flowing through the refrigerant bypass. Item 5. The heat pump device according to item 4.