JP2006038283A - Working fluid and refrigeration cycle using working fluid as refrigerant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the working fluid of high stability, high safety and high compression efficiency, and to provide a refrigeration cycle using the working fluid as the refrigerant and being easily designed and controlled. <P>SOLUTION: This working fluid is composed of a mixture including carbon dioxide and hydrocarbon of over 10 mol%, and this refrigeration cycle uses the working fluid as the refrigerant. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a working fluid composed of a mixture of carbon dioxide and hydrocarbons and a refrigeration cycle using the working fluid.

In recent years, carbon dioxide and hydrocarbons such as ammonia and propane have been used as alternative chlorofluorocarbons. At present, carbon dioxide (CO ₂ ), hydrocarbons, and the like are put into practical use as so-called natural refrigerants. Carbon dioxide is harmless at low concentrations, is nonflammable, inexpensive and stable. For this reason, it has desirable characteristics as a working fluid (for example, a refrigerant). However, since the critical temperature of carbon dioxide is 304 K (31 ° C.) and the critical pressure is 73.8 bar, when operating a refrigeration cycle using carbon dioxide as a refrigerant in the critical state, the high-pressure side pressure reaches 100 bar or more. . For this reason, in order to ensure pressure resistance and sealing performance, there is a possibility that the design of the refrigeration cycle and control during operation may become difficult. That is, in the refrigeration cycle in which the refrigerant is in a supercritical state, it is necessary to provide piping and a sealing material that can withstand high temperatures and high pressures. However, in this case, it is difficult to avoid an increase in the cost of the apparatus. Therefore, the refrigeration cycle is preferably configured as a cycle in which the refrigerant does not reach critical temperature and pressure (hereinafter referred to as a normal refrigeration cycle). However, in order to increase the refrigeration efficiency in the refrigeration cycle, Operation in a state close to the state is preferable. Moreover, it cannot be said that the compression efficiency of carbon dioxide is good during the freezing operation.

  On the other hand, although hydrocarbon is flammable, even when used as a refrigerant in the refrigeration cycle, the high-pressure side pressure of the refrigeration cycle can be suppressed to about 20 bar, and the design and control of the refrigeration cycle can be facilitated. Also, the compression efficiency of hydrocarbons is good during refrigeration operation.

  For this reason, the proposal of the refrigerating cycle using the working fluid which made the working medium the mixture of a carbon dioxide and a hydrocarbon, and compensated each other's weakness is also made | formed (for example, patent documents 1 and 2). .

However, to make use of the advantages of carbon dioxide and hydrocarbons, to make up for each other's disadvantages, and to obtain a working fluid that can constitute a normal refrigeration cycle at a wide range of outside temperatures, the criticality that changes with the mixing ratio of both is obtained. It is necessary to fully consider the temperature and critical pressure.
JP 2002-235072 A JP 2003-279181 A

  Therefore, an object of the present invention is to provide an excellent working fluid that makes use of the advantages of carbon dioxide and hydrocarbons as the working fluid and compensates for each other's disadvantages, that is, a working fluid that is stable, safe, and has good compression efficiency. In addition, an object of the present invention is to provide a refrigeration cycle in which a normal refrigeration cycle can be configured and a cycle can be easily designed and controlled by using the working fluid in a wide range of outside air conditions.

  In order to solve the above-mentioned problems, the working fluid according to the present invention comprises a mixture containing carbon dioxide and hydrocarbons exceeding 10 mol%.

  The critical temperature of the working fluid is preferably 60 ° C. or higher. If the critical temperature of the working fluid is set to 60 ° C. or higher, a normal refrigeration cycle can be configured in a wide range of outside air temperatures.

  The hydrocarbon content is preferably 10 mol% or more. If it is less than 10 mol%, the effect of raising the critical temperature cannot be sufficiently expected, and the range in which a normal refrigeration cycle can be constructed is narrowed, and it may not be possible to achieve easy refrigeration cycle design and control. On the other hand, if the hydrocarbon content exceeds 30 mol%, there is a risk that the non-flammability as the working medium cannot be sufficiently secured. Further, if it exceeds 30 mol%, the critical pressure of the refrigerant starts to drop sharply and the range in which a normal refrigeration cycle can be constructed is narrowed. Therefore, the hydrocarbon content may be 10 mol% or more and 30 mol% or less. preferable.

  The hydrocarbon is not particularly limited as long as it can achieve the above object, and preferred examples include propane, butane, and isobutane.

  Moreover, in order to solve the said subject, the refrigerating cycle which concerns on this invention consists of what uses the working fluid as described in any one of Claim 1 thru | or 3 of a claim for a refrigerant | coolant.

  As described above, the refrigeration cycle is preferably operated at a critical temperature and a critical pressure of the working fluid. By mixing carbon dioxide and hydrocarbons, the critical temperature can be maintained at a high pressure while raising the critical temperature compared to the case of carbon dioxide alone. A cycle can be configured. Therefore, the design and control of the refrigeration cycle can be facilitated.

  When a mixture having different boiling points such as carbon dioxide and hydrocarbon is used as the refrigerant, the refrigeration cycle is preferably configured as a two-way refrigeration cycle having a plurality of evaporators. As described above, if a plurality of evaporators are provided, carbon dioxide is mainly vaporized by one of the evaporators, and hydrocarbons are vaporized by the other evaporator, so that the entire refrigerant can be efficiently vaporized. it can. However, when a hydrocarbon having a boiling point close to that of carbon dioxide is used, a normal refrigeration cycle having only one evaporator may be used.

  The working fluid according to the present invention as described above can realize a working fluid that makes use of the advantages of carbon dioxide and hydrocarbons and compensates for each other's disadvantages, that is, a working fluid that is stable, safe, and has good compression efficiency. . Further, when the working fluid is used, a normal refrigeration cycle can be configured under a wide range of outside air temperature conditions, so that a refrigeration cycle that is easy to design and control the cycle can be provided.

Hereinafter, a working fluid according to the present invention and a refrigeration cycle using the working fluid will be described with reference to the drawings.
FIG. 1 shows a refrigeration cycle in which a working fluid according to the present invention is used. In FIG. 1, 1 indicates a refrigeration cycle. The refrigeration cycle 1 is formed in a cycle having a compressor 2, a condenser 3, a first evaporator 4 and a second evaporator 5.

  A first expansion valve 6 is provided on the inlet side of the first evaporator 4. A throttle valve 8 is provided on the outlet side of the first evaporator 4. On the other hand, a second expansion valve 7 is provided on the inlet side of the second evaporator 5.

  In the present embodiment, the working medium as the refrigerant is composed of a mixture of carbon dioxide and hydrocarbons having different boiling points. By providing two evaporators 4 and 5 in this way, Carbon dioxide is mainly evaporated, and hydrocarbons are mainly evaporated in the other evaporator. Therefore, the refrigerant can be efficiently and reliably vaporized.

  The working medium as a refrigerant used in this embodiment is composed of a mixture of carbon dioxide and hydrocarbon. FIG. 3 shows the change in critical temperature with respect to the content (mol%) of each hydrocarbon, and FIG. 4 shows the change in critical pressure with respect to the content (mol%) of each hydrocarbon. The results are shown in Table 1. FIG. 5 shows the change in pressure in the gas phase with respect to the content (mol%) of each hydrocarbon, and FIG. 6 shows the change in pressure in the liquid phase with respect to the content (mol%) of each hydrocarbon. .

  As can be seen from FIG. 3, butane and isobutane are effective in raising the critical temperature of the refrigerant. However, as shown in FIG. 4, when the content of butane and isobutane exceeds 30%, the critical pressure starts to decrease, so that the condition range in which a normal refrigeration cycle can be configured may be narrowed. Therefore, the content of butane and isobutane is preferably limited to about 30%.

  As shown in Table 1, in the case of substantially pure carbon dioxide, the critical temperature is 304 K (31 ° C.), and the critical pressure is 73.8 bar. However, when the butane content is 10 mol%, the critical temperature becomes 318 K (45 ° C.) and the critical pressure becomes 65 bar. By the way, the refrigerant condensing temperature is generally the outside air temperature + 15 ° C. Therefore, assuming that the outside air temperature in summer in Japan is about 30 ° C., the condensation temperature of the refrigerant can be set to 45 ° C., and a substantially normal refrigeration cycle can be configured even in the mid summer. The operating state of the cycle at this time is shown in FIG.

  Further, as can be seen from FIGS. 5 and 6, each hydrocarbon has a rich liquid phase at the same pressure. Therefore, even when the condensation temperature (outside air temperature) in the capacitor 3 is high, the refrigerant can be sufficiently liquefied.

  In this embodiment, the working medium as the refrigerant is composed of a mixture of carbon dioxide and hydrocarbons having different boiling points. For this reason, as shown in FIG. 1, the refrigeration cycle 1 is provided with two evaporators 4 and 5. By providing the two evaporators 4 and 5, carbon dioxide is mainly evaporated in one evaporator, and hydrocarbons are mainly evaporated in the other evaporator. However, when using a hydrocarbon having a boiling point close to that of carbon dioxide, the number of evaporators may be one.

  The working fluid according to the present invention can be used, for example, as a refrigerant for a refrigeration cycle of a vehicle air conditioner, a showcase, a vending machine, or the like. The refrigerating cycle according to the present invention is particularly suitable for a refrigerating cycle of an automotive air conditioner among vehicle air conditioners.

It is a schematic block diagram of the refrigerating cycle which concerns on this invention. It is a pressure-enthalpy diagram of the refrigerating cycle of FIG. FIG. 2 is a relationship diagram illustrating a relationship between a hydrocarbon content of a refrigerant in the refrigeration cycle of FIG. 1 and a critical temperature. FIG. 2 is a relationship diagram illustrating a relationship between a hydrocarbon content of a refrigerant in the refrigeration cycle of FIG. 1 and a critical pressure. FIG. 2 is a relationship diagram illustrating a relationship between a hydrocarbon content and pressure when the refrigerant in the refrigeration cycle in FIG. 1 is in a gas phase state. FIG. 2 is a relationship diagram illustrating a relationship between a hydrocarbon content and a pressure when a refrigerant in the refrigeration cycle in FIG. 1 is in a liquid phase state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Refrigeration cycle 2 Compressor 3 Condenser 4 1st evaporator 5 2nd evaporator 6 1st expansion valve 7 2nd expansion valve 8 Throttle valve

Claims (5)

  A working fluid comprising a mixture containing carbon dioxide and more than 10 mol% hydrocarbon.   The working fluid according to claim 1, wherein the critical temperature is 60 ° C. or higher.   The working fluid according to claim 1 or 2, wherein the hydrocarbon is propane, butane, or isobutane.   The working fluid according to any one of claims 1 to 3, wherein the hydrocarbon content is 10 mol% or more and 30 mol% or less. A refrigeration cycle using the working fluid according to any one of claims 1 to 5 as a refrigerant.

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