Low-temperature and average-temperature refrigeration

Abstract

The invention relates to the use of binary compositions of 2,3,3,3-tetrafluoropropene and difluoromethane as a heat transfer fluid in compression, low-temperature and average temperature refrigeration systems, with exchangers operating in counterflow mode or in split flow mode with counterflow tendency. The invention also relates to a heat transfer method.

Description

[0001] The present invention relates to the use of binary compositions of 2,3,3,3-tetrafluoropropene and difluoromethane as heat transfer fluids.

[0002] The problems posed by ozone-depleting substances (ODPs) were addressed in Montreal, where a protocol was signed mandating a reduction in the production and use of chlorofluorocarbons (CFCs). This protocol has since been amended, requiring the phasing out of CFCs and extending regulations to other products, including hydrochlorofluorocarbons (HCFCs).

[0003] The refrigeration and air conditioning production industry has invested heavily in substituting these refrigerants, and that is how hydrofluorocarbons (HFCs) were commercialized.

[0004] In the automotive industry, air conditioning systems in vehicles sold in many countries have switched from chlorofluorocarbon (CFC-12) refrigerant to hydrofluorocarbon (HFC-134a), which is less harmful to the ozone layer. However, in light of the objectives set by the Kyoto Protocol, HFC-134a (GWP = 1300) is considered to have a high global warming potential. A fluid's contribution to the greenhouse effect is quantified by a criterion called the GWP (Global Warming Potential), which summarizes its warming potential using a reference value of 1 for carbon dioxide.

[0005] Carbon dioxide, being non-toxic, non-flammable, and having a very low GWP, has been proposed as a refrigerant for air conditioning systems to replace HFC-134a. However, the use of carbon dioxide presents several drawbacks, particularly related to the very high pressure required for its use as a refrigerant in existing equipment and technologies.

[0006] Furthermore, the R-404A blend, consisting of 44% by weight pentafluoroethane, 52% by weight trifluoroethane, and 4% by weight HFC-134a, is widely used as a refrigerant in large retail spaces (supermarkets) and in refrigerated transport. However, this blend has a GWP of 3900.

[0007] Document JP 4110388 describes the use of hydrofluoropropenes of formula C3HmFn, with m, n representing an integer between 1 and 5 inclusive and m + n = 6, as heat transfer fluids, in particular tetrafluoropropene and trifluoropropene.

[0008] Document WO2004 / 037913 discloses the use of compositions comprising at least one fluoroalkene having three or four carbon atoms, in particular pentafluoropropene and tetrafluoropropene, preferably having a GWP of no more than 150, as heat transfer fluids.

[0009] Document WO 2006 / 094303 discloses an azeotropic composition containing 7.4 wt% of 2,3,3,3-tetrafluoropropene (HFO-1234yf) and 92.6 wt% of difluoromethane (HFC-32). This document also discloses quasi-azeotropic compositions containing from 1 to 57 wt% of 2,3,3,3-tetrafluoropropene and from 43 to 99 wt% of difluoromethane.

[0010] US 2008 / 314073 describes a method for detecting leakage of a heat transfer composition in a closed circuit equipped with a device for measuring the internal pressure of the system.

[0011] FR 2182956 describes a specific cross-counterflow heat exchanger.

[0012] FR 2256381 describes a heat transmission device comprising a heat pump assembly.

[0013] A heat exchanger is a device that transfers thermal energy from one fluid to another without mixing them. The heat flows through the exchange surface that separates the fluids. This method is most often used to cool or heat a liquid or gas that cannot be cooled or heated directly.

[0014] In compression systems, heat exchange between the refrigerant and the heat sources occurs via heat transfer fluids. These heat transfer fluids are in a gaseous state (air in air conditioning and direct expansion refrigeration), a liquid state (water in domestic heat pumps, glycol water) or a two-phase state.

[0015] There are different transfer methods: The two fluids are arranged parallel and flow in the same direction: co-current (counter-current) flow; the two fluids are arranged parallel but flow in opposite directions: counter-current (counter-current) flow; the two fluids are positioned perpendicularly: cross-flow flow. The cross-flow can be co-current or counter-current; one of the two fluids makes a U-turn in a wider conduit, which the second fluid then passes through. This configuration is comparable to a co-current heat exchanger for half its length, and to a counter-current heat exchanger for the other half: pinhead flow.

[0016] The applicant has now discovered that binary compositions of 2,3,3,3-tetrafluoropropene and difluoromethane are of particular interest as heat transfer fluids in compression systems for low and medium temperature refrigeration, with exchangers operating in counter-current mode or in cross-flow mode with a counter-current tendency.

[0017] Thus, these compositions can be used as a heat transfer fluid in refrigeration of refrigerated vehicles, in food preservation and in industry (chemical, food etc.) with counter-current or cross-flow mode heat exchangers with a counter-current tendency.

[0018] A first object of the present invention relates to the use of binary compositions of 2,3,3,3-tetrafluoropropene and difluoromethane as a heat transfer fluid in compression systems for low and medium temperature refrigeration, with exchangers operating in counter-current mode or in cross-flow mode with a counter-current tendency.

[0019] Low and medium temperature refrigeration refers to the range of -45°C to -10°C at the evaporator.

[0020] Preferably, the binary compositions of 2,3,3,3 tetrafluoropropene and difluoromethane contain essentially 61 to 85% by weight of 2,3,3,3-tetrafluoropropene and 15 to 39% by weight of difluoromethane.

[0021] Advantageously, the binary compositions contain essentially 70 to 79% by weight of 2,3,3,3 tetrafluoropropene and 21 to 30% by weight of difluoromethane.

[0022] The binary compositions used in the present invention have both a zero ODP and a low GWP. The coefficient of performance (COP: the ratio of cooling capacity to electrical consumption of a refrigerator) of these binary compositions in counterflow heat exchangers is higher than that of compositions currently used in low- and medium-temperature refrigeration. Given the condenser pressure level, it is not necessary to develop new compressors; existing commercially available compressors are suitable.

[0023] The binary compositions used in the present invention can replace R-404A and R-407C (ternary mixture containing 52 wt% of HFC-134a, 25 wt% of pentafluoroethane and 23 wt% of difluoromethane) in compression heat transfer systems with exchangers operating in counter-current mode or in cross-flow mode with a counter-current tendency.

[0024] The binary compositions implemented according to the present invention can be stabilized. The quantity of stabilizer preferably represents at most 5% by weight relative to the binary composition.

[0025] Examples of stabilizers include nitromethane, ascorbic acid, terephthalic acid, azoles such as tolutriazole or benzotriazole, phenolic compounds such as tocopherol, hydroquinone, t-butyl hydroquinone, 2,6-di-ter-butyl-4-methylphenol, epoxides (alkyl, possibly fluorinated or perfluorinated, alkenyl or aromatic) such as n-butyl glycidyl ether, hexanediol diglycidyl ether, allyl glycidyl ether, butylphenyl glycidyl ether, phosphites, phosphates, phosphonates, thiols and lactones.

[0026] A second object of the present invention relates to a heat transfer process in compression systems for low and medium temperature refrigeration, in which the binary compositions of 2,3,3,3 tetrafluoropropene and difluoromethane, as defined above, are used as refrigerant with exchangers operating in counter-current mode or in cross-flow mode with a counter-current tendency.

[0027] The process according to the present invention can be implemented in the presence of lubricants such as mineral oil, alkylbenzene, polyalkylene glycol, polyol ester and polyvinyl ether. EXPERIMENTAL SECTION Calculation tools

[0028] The RK-Soave equation is used to calculate the densities, enthalpies, entropies, and liquid-vapor equilibrium data of mixtures. Using this equation requires knowledge of the properties of the pure substances used in the mixtures in question, as well as the interaction coefficients for each binary component.

[0029] The data required for each pure substance are: Boiling point, critical temperature and pressure, pressure-temperature curve from boiling point to critical point, saturated liquid and saturated vapor densities as a function of temperature. HFC-32:

[0030] Data on HFC-32 is published in the ASHRAE Handbook 2005 chapter 20, and is also available under Refrop (Software developed by NIST for calculating the properties of refrigerants) HFO - 1234yf:

[0031] The temperature-pressure curve data for HFO-1234yf are measured using the static method. Critical temperature and pressure are measured using a C80 calorimeter commercially available from Setaram. Densities at saturation as a function of temperature are measured using vibrating tube densitometer technology developed by the laboratories of the École des Mines de Paris. Binary interaction coefficient of HFC-32 / HFO-1234yf:

[0032] The RK-Soave equation uses binary interaction coefficients to represent the behavior of products in mixtures. The coefficients are calculated based on experimental liquid-vapor equilibrium data. The technique used for liquid-vapor equilibrium measurements is the analytical static cell method. The equilibrium cell consists of a sapphire tube and is equipped with two electromagnetic ROLSITM samplers. It is immersed in a cryo-thermostat bath (HUBER HS40). Variable-speed rotating magnetic field-driven stirring is used to accelerate the achievement of equilibrium. Sample analysis is performed by gas chromatography (HP5890 series II) using a thermal conductivity detector (TCD).

[0033] Liquid-vapor equilibrium measurements on the HFC-32 / HFO-1234yf binary system are performed for the following isotherms: -10°C, 30°C and 70°C Compression system

[0034] Consider a compression system equipped with a counter-current evaporator and condenser, a screw compressor and an expansion valve.

[0035] The system operates with 15°C of superheat and 5°C of subcooling. The minimum temperature difference between the secondary fluid and the refrigerant is considered to be around 5°C.

[0036] The isentropic efficiency of compressors is a function of the compression ratio. This efficiency is calculated using the following equation: η isen = a − b τ − c 2 − d τ − c

[0037] For a screw compressor, the constants a, b, c, d and e of equation (1) of isentropic efficiency are calculated according to the standard data published in the Handbook "Handbook of air conditioning and refrigeration, page 11.52".

[0038] The coefficient of performance (COP) is defined as the useful power supplied by the system divided by the power supplied or consumed by the system.

[0039] The Lorenz coefficient of performance (COPLorenz) is a reference coefficient of performance. It is a function of temperature and is used to compare the COPs of different fluids.

[0040] The Lorenz coefficient of performance is defined as follows: (Temperatures T are in K)

[0041] T moyenne condenseur = T entrée condenseur − T sortie condenseur T moyenne évaporateur = T sortie évaporateur − T entrée évaporateur

[0042] The Lorenz COP in the case of air conditioning and refrigeration: COPlorenz = T moyenne évaporateur T moyenne condenseur − T moyenne évaporateur

[0043] The Lorenz coefficient of performance (COP) in the case of heating: COPlorenz = T moyenne condenseur T moyenne condenseur + T moyenne évaporateur

[0044] For each composition, the Lorenz cycle performance coefficient is calculated based on the corresponding temperatures.

[0045] The %COP / COPLorenz is the ratio of the system's COP to the COP of the corresponding Lorenz cycle. Results in low-temperature refrigeration mode

[0046] In low-temperature mode, the compression system operates between a refrigerant inlet temperature at the evaporator of -30°C and a refrigerant inlet temperature at the condenser of 40°C. The system provides cooling at -25°C.

[0047] The performance of the compositions according to the invention under low temperature operating conditions is given in Table 1. The values ​​of the constituents (HFO-1234yf, HFC-32) for each composition are given as a percentage by weight. Results in medium temperature refrigeration mode

[0048] In medium temperature mode, the compression system operates between a refrigerant inlet temperature at the evaporator of -15°C and a refrigerant inlet temperature at the condenser of 35°C. The system provides cooling down to -10°C.

[0049] The performance of the binary compositions under medium temperature operating conditions is given in Table 2. The values ​​of the constituents (HFO-1234yf, HFC-32) for each composition are given as a percentage by weight.

Claims

1. Use of a binary composition containing 2,3,3,3-tetrafluoropropene and difluoromethane as heat transfer fluid in compression-type, low- and medium-temperature refrigeration systems, with exchangers operating in countercurrent mode or in crossed-current mode with countercurrent tendency.

2. Use according to Claim 1, characterized in that the composition contains essentially from 61 to 85 wt.% of 2,3,3,3-tetrafluoropropene and from 15 to 39 wt.% of difluoromethane.

3. Use according to Claim 1, characterized in that the composition contains essentially from 70 to 79 wt.% of 2,3,3,3-tetrafluoropropene and from 21 to 30 wt.% of difluoromethane.

4. Method of heat transfer in which a binary composition containing 2,3,3,3-tetrafluoropropene and difluoromethane is used as refrigerant in compression-type low- and medium-temperature refrigeration systems, with exchangers operating in countercurrent mode or in crossed-current mode with countercurrent tendency.

5. Method according to Claim 4, characterized in that the composition contains essentially from 61 to 85 wt.% of 2,3,3,3-tetrafluoropropene and from 15 to 39 wt.% of difluoromethane.

6. Method according to Claim 4, characterized in that the composition contains essentially from 70 to 79 wt.% of 2,3,3,3-tetrafluoropropene and from 21 to 30 wt.% of difluoromethane.

7. Method according to Claims 4 to 6, characterized in that the binary composition is stabilized.

8. Method according to any one of Claims 4 to 7, characterized in that it is implemented in the presence of a lubricant.