JP4154454B2 - Refrigeration equipment - Google Patents

Description

The present invention relates to a refrigeration apparatus using a composition for a refrigeration cycle using a hydrofluorocarbon-based refrigerant .

  Fluorocarbon containing chlorine such as dichlorodifluoroethane (hereinafter referred to as CFC12), monochlorodifluoromethane (hereinafter referred to as HCFC22), or R-502, which is an azeotropic mixture of HCFC22 and CFC115, is used as a refrigerant that leads to destruction of the ozone layer. become unable. Therefore, as alternative fluorocarbons, difluoromethane (hereinafter referred to as HFC32), pentafluoroethane (hereinafter referred to as HFC125), 1,1,1,2-tetrafluoroethane (hereinafter referred to as HFC134a), 1,1,1-tri Hydrofluorocarbon refrigerants that do not destroy the ozone layer, such as fluoroethane (hereinafter referred to as HFC143a) and 1,1-difluoroethane (hereinafter referred to as HFC152a), have been studied as a single substance or a mixture. At the same time, the development of a refrigeration system using this hydrofluorocarbon refrigerant is urgently needed.

The refrigeration apparatus is represented by an air conditioner, a refrigerator, or the like in which a refrigeration cycle having four actions of evaporation, compression, condensation, and expansion is incorporated. In the refrigeration cycle, the refrigerant circulates while repeating changes from liquid to gas and from gas to liquid. Also, refrigeration oil and desiccant are included in the system. Here, the refrigeration oil is used particularly for lubrication in the compression mechanism, but is required as a characteristic that requires compatibility with the refrigerant because of oil return in the cycle. However, since the above-mentioned alternative chlorofluorocarbon hardly dissolves in mineral oil, which is a conventional refrigerator oil, attempts have been made to use refrigerator oils such as polyol ester oils and polyether oils that are soluble in hydrofluorocarbon refrigerants. Yes. In addition, there are polyalkylene glycol oils and polyalkylbenzene oils. In addition, the desiccant is filled in the dryer for the purpose of reducing the moisture concentration in the cycle and mounted in the refrigeration cycle. Conventionally, this desiccant is a sodium A-type zeolite, which is called type 4A, and has been used in a refrigeration cycle composed of CFC12, R-502, HCFC22 refrigerant and mineral oil (for example, see Patent Document 1).
Kawahira, Y., “Enclosed Refrigerator”, Japan Refrigeration Association, April 30, 1993, p. 189-191

  Both the above-mentioned alternative chlorofluorocarbons and refrigeration oils such as polyester-based oils and polyether-based oils suitable for these alternative chlorofluorocarbons have characteristics of high water absorption, and a large amount of water may be mixed in the refrigeration cycle. If moisture is mixed in, it is expected to freeze in the capillary tube, hydrolyze refrigerant / refrigerant oil, material deterioration due to acid components generated in the cycle, generation of contamination, etc. Water removal is an important issue in refrigeration cycles using polyester oils or polyether oils.

  However, when conventional sodium A-type zeolite is used in a refrigeration cycle using alternative chlorofluorocarbons for the purpose of reducing the moisture concentration in the cycle, HFC32 alone or HFC32-containing mixed chlorofluorocarbons are decomposed, and at the same time, A-type zeolite is also affected. However, there is a problem that moisture removal is not sufficient.

The present invention has been made to cope with such a problem, and can reduce the moisture concentration in the refrigeration cycle without decomposing alternative chlorofluorocarbons and does not adversely affect the sliding mechanism. It aims at providing the freezing apparatus using the composition for refrigerating cycles .

In the present invention, the composition for a refrigeration cycle refers to an aggregate of refrigerant, refrigeration oil, desiccant and the like used in the refrigeration cycle.

The refrigerating apparatus of the present invention includes a refrigerant, a refrigerating machine oil, and a desiccant, a compression mechanism that compresses the refrigerant, a condensing mechanism that cools the compressed refrigerant, and an expansion mechanism that expands the condensed refrigerant. In the refrigeration apparatus having a closed refrigeration cycle comprising an evaporation mechanism for evaporating the expanded refrigerant, the refrigerant is hydrofluorocarbon containing difluoromethane , and the desiccant is sodium / potassium A-type zeolite. The amount of sodium is 6% by weight or more, the amount of potassium is 5% by weight or more, and the total amount of sodium and potassium is 13 to 20% by weight.

The composition for a refrigeration cycle used in the present invention is a sodium / potassium A-type zeolite desiccant having a sodium content of 6% by weight or more, a potassium content of 5% by weight or more, and a total of sodium and potassium. Since the amount is 13 to 20% by weight and the average pore diameter is 0.3 nm or less, the amount of adsorption of HFC32 is particularly small, and thermal decomposition of HFC32 hardly occurs. As a result, it is useful as a composition for a refrigeration cycle containing at least HFC32.

ADVANTAGE OF THE INVENTION According to this invention, a deposit etc. are not produced | generated in a refrigerating cycle, but the refrigeration apparatus excellent in durability can be obtained.

  The hydrofluorocarbon refrigerant according to the present invention is a compound composed of carbon, fluorine and hydrogen, which can replace the conventional refrigerants CFC12 and HCFC22. For example, HFC32, HFC125, HFC134a, HFC143a, HFC152a, etc. can be illustrated. These hydrofluorocarbons can be used alone or as a mixture of two or more. Among these refrigerants, a hydrofluorocarbon having a small molecular diameter is preferable, and a hydrofluorocarbon containing at least HFC32 is particularly preferable. Preferred hydrofluorocarbons include mixed refrigerants such as HFC32 / HFC125, HFC32 / HFC152a, HFC32 / HFC134a, HFC32 / HFC125 / HFC134a, HFC32 / HFC125 / HFC134a / R290, and HFC32 single refrigerant.

  A preferred desiccant according to the present invention is a sodium / potassium A type pure synthetic zeolite comprising sodium aluminosilicate. In general, A-type zeolite is a pure synthetic zeolite that is not found in nature, and has a fixed pore size close to a relatively simple molecular size, and is characterized by adsorbing only molecules whose molecular size is smaller than this pore size. Have For this reason, it is also called molecular sieve or molecular sieve and is used as a desiccant for refrigerants. The A type zeolite includes sodium A type zeolite called 4A type mainly containing sodium as a cation in zeolite, and potassium A type zeolite called 3A type mainly containing potassium as a cation.

  The molecular sieve pore diameter is limited by metal ions (Na, K, Ca, etc.) located near the maximum oxygen ring, and the number and position of metal ions or the change in ion radius due to ion exchange As it happens, the pore size changes accordingly. For example, the pore size in sodium A type is about 0.4 nm, but potassium A type substituted with K (theoretical radius: 0.152 nm) having a larger ionic radius than the ionic radius of Na (theoretical radius: 0.116 nm). Has a pore diameter of about 0.3 nm. Comparing the theoretical molecular diameters of hydrofluorocarbon and water, HFC32 having the smallest theoretical molecular diameter among hydrofluorocarbons is 0.33 nm and water is 0.28 nm. Therefore, potassium A-type zeolite has been considered suitable as a desiccant used in the hydrofluorocarbon refrigeration cycle composition.

  However, as a result of using potassium A-type zeolite desiccant in the composition for hydrofluorocarbon refrigeration cycle, a preferable result was not necessarily obtained. On the other hand, as a result of various investigations on the ratio of sodium cation to potassium cation of conventional sodium A-type zeolite, the use of sodium-potassium A-type zeolite containing a predetermined amount of sodium and potassium cation reduces the amount of HFC32 adsorbed and decomposes. Did not occur. The present invention has been made based on such findings.

The desiccant according to the present invention is a substance having an HFC32 adsorption amount of less than 2.77% by weight according to the McBain method. When the amount of adsorption is 2.77% by weight or more, decomposition of HFC32 is likely to occur, which is not preferable. A more preferable amount of adsorption that does not cause decomposition of HFC32 is 1.5% by weight or less. Examples of such a desiccant include sodium / potassium A-type zeolite .

  The sodium / potassium A-type zeolite according to the present invention is a pure synthetic zeolite made of sodium aluminosilicate, the amount of sodium is 6% by weight or more, the amount of potassium is 5% by weight or more, and the total amount of sodium and potassium is When the amount is in the range of 13 to 20% by weight, the adsorption amount of HFC32 can be lowered, and the water concentration in the refrigeration cycle can be lowered. More preferable ranges for lowering the adsorption amount and the water concentration are a sodium amount of 7% by weight or more, a potassium amount of 6% by weight or more, and a total amount of sodium and potassium of 13 to 16% by weight.

  The refrigeration apparatus of the present invention has a refrigeration cycle using a desiccant having an HFC32 adsorption amount of less than 2.77% by weight according to the McBain method. By using such a desiccant, only moisture can be adsorbed and removed without adsorbing the refrigerant in the refrigeration cycle, so that icing in the capillary tube, hydrolysis of refrigerant / refrigerant oil, generated in the cycle Material deterioration due to acid components, generation of contamination, etc. can be suppressed. Examples of the refrigeration apparatus of the present invention include a refrigerator, an air conditioner, a showcase, an in-vehicle refrigerator, a vending machine, a beer server, and the like.

  The refrigerating machine oil according to the present invention can be used as long as it has compatibility with a hydrofluorocarbon refrigerant. Preferred refrigerating machine oils include polyol ester oils, polyether oils, fluorine oils, polyalkylene glycols and the like. Alkylbenzene oils and mineral oils with low compatibility can also be used.

  There are metal ions (cations: Na, K, Ca, etc.) in zeolite that are located where they do not participate in molecular sieving, and those that exist in pores that affect molecular sieving. The latter metal ion species is considered to cause a change in pore diameter. The sodium / potassium A-type zeolite according to the present invention is considered to be capable of exchanging Na ions, which affect molecular sieving action, with K ions. For this reason, it has a pore diameter (0.3 nm or less) equal to or less than that of potassium A-type zeolite. Therefore, only moisture can be adsorbed and removed without adsorbing the refrigerant in the refrigeration cycle. Further, since the adsorption is difficult to occur, the thermal decomposition of the HFC 32 is difficult to occur. As a result, deterioration of the refrigeration cycle constituent material, generation of contamination, etc. can be suppressed.

Example 1
The amount of HFC32 adsorbed on the sodium / potassium A-type zeolite according to the present invention was measured by the McBain method. The measurement results are shown in Table 1 together with the amounts of Na and K of the test sodium / potassium A-type zeolite. In addition, the measurement result of sodium A type zeolite (4A type) and potassium A type zeolite (3A type) is shown simultaneously as a comparative example.

  From the results shown in Table 1, it can be seen that sodium-potassium A-type zeolite has a significantly small amount of adsorption of HFC32. This indicates that the sodium / potassium A-type zeolite according to the present invention easily adsorbs only water, and HFC32 is hardly decomposed.

  Table 2 shows the measurement results of the decomposition rate of HFC32 by the autoclave test. The autoclave test is a thermostatic bath in which about 10 g of ester-based refrigeration oil, 10 g of refrigerant HFC32, and about 100 g of zeolite sample are sealed in a stainless pressure vessel (240 ml), and the temperatures are kept at 60, 120, and 175 ° C., respectively. Aged for 500 hours. After aging for 500 hours, a zeolite sample was taken out and the decomposition rate of the refrigerant HFC32 was measured. The decomposition rate of the refrigerant HFC32 is expressed as a percentage by dividing F ions contained in the zeolite sample by the amount of F atoms in the refrigerant HFC32.

  From the results in Table 2, the sodium / potassium A-type zeolites of Samples C to E are less likely to decompose the refrigerant HFC32 even at a high temperature of 175 ° C. compared to the zeolites of Samples A and B. In particular, Sample C and Sample D in which the amount of sodium is 7% by weight or more, the amount of potassium is 6% by weight or more, and the total amount of sodium and potassium is 14.4% by weight and 13% by weight are 175 ° C. Also in the autoclave test, it can be seen that the decomposition rate of HFC32 is as low as about 2%, which is particularly excellent. Among sample C and sample D, sample C is most suitable in which the amount of sodium is 7.9% by weight or more, the amount of potassium is 6.5% by weight or more, and the total amount of sodium and potassium is 14.4% by weight. ing.

  Therefore, in the refrigeration cycle of HFC-based refrigerants, particularly HFC32 alone or a mixed refrigerant containing HFC32, the water in the refrigeration cycle is removed by using the sodium / potassium A-type zeolite according to the present invention as a desiccant. Thus, the reliability of the refrigeration cycle can be improved.

  Next, the fracture strength and wear rate of the above zeolite samples were measured by the following test methods. The fracture strength was determined by compressive strength measurement, and the wear rate was determined by the weight ratio reduced by the paint shaker method. The results are shown in Table 3.

  From the results in Table 3, sodium / potassium A-type zeolite has a high average fracture strength and a low wear rate. This indicates that destruction of the desiccant in the refrigeration cycle hardly occurs and fine powder is hardly generated. As described above, the composition for a refrigeration cycle of the present invention has the characteristics of adsorbing moisture without decomposing HFC32, excellent thermal stability, and strong mechanical strength.

Example 2
The refrigerator according to the present invention will be described with reference to FIG. 1, taking a refrigerator as an example. FIG. 1 is a diagram showing a refrigeration cycle. The hydrofluorocarbon refrigerant is compressed by a compressor 3 as a compression mechanism, cooled through a receiving pipe 4, a heat radiating pipe 5, and a clean pipe 6 as a condensation mechanism, and then passes through a capillary tube 1 as an expansion mechanism via a dryer 8. It expands and evaporates in the evaporator 2 which is an evaporation mechanism, and the inside of the refrigerator 7 is cooled. Thereafter, it is compressed again by the compressor 3.

  In this example, HFC32 / HFC134a was used as the refrigerant, polyol ester was used as the refrigerating machine oil, and sodium / potassium A-type zeolite having an HFC32 adsorption amount of 1.0 wt% or less by the Macbain method was filled in the dryer 8. The sodium / potassium A-type zeolite had a sodium content of 7.9% by weight and a potassium content of 6.5% by weight. This refrigerator was operated at 2000C for 2000 hours.

  During operation, no abnormal noise was generated from the compressor 3, and the compressor sliding part was not damaged. In addition, after the operation was completed, the capillary tube in the refrigeration cycle was disassembled and the deposit generation state was investigated, but almost no deposit was found in the capillary tube. Furthermore, the amount of water in the refrigeration oil did not change compared to when the operation was started.

It is a figure which shows a refrigerating cycle.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Capillary tube, 2 ... Evaporator, 3 ... Compressor, 4 ... Receptacle pipe, 5 ... Radiation pipe, 6 ... Clean pipe, 7 ... Refrigerator, 8 ... Dryer

Claims (1)

A compression mechanism for compressing the refrigerant; a condensation mechanism for cooling the compressed refrigerant; an expansion mechanism for expanding the condensed refrigerant; and evaporating the expanded refrigerant. In a refrigeration apparatus having a closed refrigeration cycle comprising an evaporation mechanism
The refrigerant is a hydrofluorocarbon containing difluoromethane, said drying agent is a sodium-potassium A zeolite, sodium weight of 6 wt% or more, the potassium content is 5 wt% or more and the sodium and potassium The total amount is 13 to 20% by weight.

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