HK1085505A - Refrigerant compositions - Google Patents

Description

Refrigerant composition

The present invention relates to refrigerant compositions, particularly low temperature refrigerants for cold storage.

There is a need for a cryogenic refrigerant for cold storage that has been met by R502 and the azeotropic mixtures of R115 and R22 prior to the Montreal Protocol. Such refrigerants are particularly attractive at low temperatures where either R12(CCl2F2) or R22 reach their effective operating limits, where a dramatic increase in refrigeration capacity is possible, and the main advantage of using R22 is the ability to operate at suitably lower discharge temperatures, but are not currently available because R502 contains the severe ozone depleting agent R115.

It has surprisingly been found that this need can be partially met by using two mixtures containing R143a, the first being R404A, which consists of R125 (44% w/w), R143a (52% w/w) and R134a (4% w/w). The second is R507A, which consists of an azeotrope of R125 (50% w/w) and R143a (50% w/w).

The problem with using the above mixtures is that they have very high Global Warming Potentials (GWPs).

The concept of Global Warming Potential (GWP) is presented to compare the ability of greenhouse gases and other gases to capture heat in the atmosphere. Mixing carbon dioxide (CO)₂) Selected as the reference gas. Because GWP's are proportional, there is no dimension. GWP's cited below were obtained from IPCC-1995 at a time of 100 years. The GWP's of the mixtures are calculated by the product of the total mass fraction and the GWP of the individual components.

Greenhouse gases are gases that cause the earth's atmosphere to capture heat. Greenhouse gases allow solar radiation to reach the earth's surface. The earth's surface is heated by this radiation and emits longer wavelength infrared radiation due to this heating. Greenhouse gases prevent this radiation from escaping to space by absorbing it, thus sealing the heat to the atmosphere.

The GWP of R507 is 3300, and slightly lower R404A is 3260. These higher GWP's are due to the presence of R143 a. The GWP of pure R143a compared to the other main component R125 was 3800, and the GWP of R125 was only 2800.

R22 was also used alone, but it was an ozone depleting substance and will be rejected the next decade. While R22 is not efficient at the low temperatures required for cold storage.

There is currently considerable concern over global warming and it is therefore important to use mixtures of as low GWP as possible. It is clearly desirable to find an alternative to R502 that is non-ozone depleting, has a low GWP, and can operate more efficiently at lower temperatures than required for R22, R404A, or R507.

The present invention provides a refrigerant composition comprising:

(a) pentafluoroethane, trifluoromethoxydifluoromethane or hexafluoro-cyclopropane, or a mixture of two or more thereof, in an amount of at least 75% based on the weight of the composition,

(b)1, 1, 1, 2-or 1, 1, 2, 2-tetrafluoroethane, trifluoromethoxy pentafluoroethane, 1, 1, 1, 2, 3, 3-heptafluoropropane or a mixture of two or more thereof in an amount of from 5 to 24% by weight, based on the weight of the composition, and

(c) an ethylenically unsaturated or saturated hydrocarbon, optionally containing one or more oxygen atoms, having a boiling point of from-50 ℃ to +35 ℃, or mixtures thereof, in an amount of from 1% to 4% by weight, based on the weight of the composition, the weight ratio of component (a) to component (b) being at least 3: 1.

The percentages mentioned above refer in particular to the percentages in the liquid phase. The corresponding ranges for the vapor phase are as follows: (a) at least 85%, (b)2 to 12% and (c)0.8 to 3%, all by weight of the composition. The percentages are preferably used in the liquid and vapor phases.

The present invention also provides a method of producing refrigeration comprising condensing a composition of the present invention and thereafter evaporating said composition in the vicinity of the cooled body portion. The present invention also provides a refrigeration device comprising as a refrigerant a composition of the present invention.

Component (a) is present in an amount of at least 75% by weight of the composition. In practice, the concentration is generally at least 80% by weight, preferably in the range 80 to 90% by weight, especially 83 to 88% by weight, more especially about 85% by weight. Preferably component (a) is R125 (pentafluoroethane) or a mixture containing at least half, especially at least 3/4 (mass), of R125. The most preferred component (a) is R125 (alone). Generally, the refrigeration capacity of the composition increases with increasing R125 content; the best cooling capacity and effect is achieved at about 85% R125.

Component (b) is present in the composition in an amount of from 5 to 24% by weight, based on the weight of the composition. Typically, the amount of this component is from 7.5% to 20%, typically from 10% to 15% by weight, especially about 11.5% by weight. Component (b) preferably comprises at least half, in particular at least 3/4 (by mass), of a mixture of R134a (1, 1, 1, 2-tetrafluoroethane). Most preferably component (b) is R134a (alone).

The weight ratio of component (a) to component (b) is at least 3: 1, usually at least 4: 1, preferably from 5: 1 to 10: 1, in particular from 7: 1 to 9: 1.

Component (c) is a saturated or ethylenically unsaturated hydrocarbon, optionally containing one or more oxygen atoms, in particular an oxygen atom, having a boiling point of from-50 ℃ to +35 ℃, or a mixture thereof. Preferred hydrocarbons which may be used have from 3 to 5 carbon atoms and may be cyclic or acyclic. Acyclic hydrocarbons which may be used include propane, n-butane, isobutane, pentane, isopentane and dimethyl ether and ethyl methyl ether, and propane. Cyclic hydrocarbons that may be used include cyclobutane, cyclopropane, methylcyclopropane, and oxetane. Preferred hydrocarbons include n-butane and isobutane, with isobutane being particularly preferred. Isobutane is particularly suitable for producing non-combustible mixtures in the worst case of predetermined leak-off fractionation.

The presence of at least one further component in the composition is not excluded, and thus although the composition typically comprises three main components, at least a fourth component may be present. Typical fourth components include additional fluorocarbons, and especially hydrofluorocarbons, for example boiling points at atmospheric pressure of up to-40 ℃, preferably up to-49 ℃, especially those in which the F/H ratio in the molecule is at least 1, preferably R23, trifluoromethane, most preferably R32, difluoromethane. Usually the maximum concentration of the above-mentioned further components is not more than 10%, in particular not more than 5%, more in particular not more than 2% by weight, based on the sum of the weights of components (a), (b) and (c). The presence of hydrofluorocarbons generally has a neutral effect on the desired properties of the formulation. It is desirable that the butane or butanes, especially n-butane or isobutane, represent at least 70%, preferably at least 80%, more preferably 90% by weight of the total weight of hydrocarbons in the composition. It will be appreciated that it is preferred to avoid the use of perhalogenated carbons in order to reduce any greenhouse effect and to avoid the use of hydrogen-containing halocarbons with one or several halogen atoms heavier than fluorine. The total amount of the above halocarbons is advantageously not more than 2%, in particular 1% and more particularly not more than 0.5% by weight.

The compositions of the present invention have also been found to be extremely compatible with mineral oil lubricants that are conveniently used with CFC refrigerants. The compositions of the invention can therefore be used not only with completely synthetic lubricants such as esters of polyhydric alcohols (POE), polyalkylene glycols (PAG) and polyoxypropylene glycols or fluorinated oils as described in EP-A-399817, but also with mineral and alkylbenzene lubricants including naphthalene, paraffin and silicone oils and mixtures of said oils and completely synthetic lubricants and fluorinated oils.

Typical additives which may be used include "extreme pressure" and antiwear additives, oxidation and thermal stability improvers, corrosion inhibitors, viscosity index improvers, pour point depressants, detergents, antifoams and viscosity modifiers. Examples of suitable additives are included in table D of US-A-4755316.

The following examples further illustrate the invention.

Examples

Determination of the vapor pressure/temperature relationship of the mixtures used for the tests

The samples used for the tests are detailed in table 1.

Apparatus and test

The apparatus for determining the vapour pressure/temperature relationship consisted of a 1 liter Parr reactor (Parr reactor) completely immersed in a thermally stable controlled water bath. The bath temperature was measured using a graduated platinum resistance thermometer with an isotechti 1 indicator. The resolution of the thermometer was 0.01 ℃. The pressure was read using a graduated pressure transducer with a test accuracy of 0.01 bar and read on a Druck DR1 instrument.

Approximately 1.2kg of refrigerant was added to the parr reactor, which was cooled overnight and when the temperature was reached, the pressure and temperature were recorded every ten minutes until constant.

The data obtained do not give dew point and therefore no glide (glide). A rough estimate of slip is obtained using the REFPROP 6 program, and the slip versus bubble point is generally nearly linear and can be expressed in a linear equation. In the case of R407C, a binomial equation must be used. The equation can be used to give an approximate slip for the experimentally determined bubble point. It is effective to normalize the calculated slip to experimentally determined data. The dew point can then be estimated using the temperature/pressure relationship, and the bubble point can again be found. The slip equations obtained are also shown in Table 2. The equation can be used to derive a vapor pressure/temperature table.

Determination of refrigerant Performance on Low Temperature (LT) calorimeter

Equipment and general operating conditions

The performance of the refrigerant was measured on a Low Temperature (LT) calorimeter. The LT calorimeter was equipped with a Bitzer semi-sealed condensing unit containing Shell SD oil. The hot vapor exits through the compressor, passes through an oil separator, and enters the condenser. The discharge pressure at the compressor outlet is kept constant by closing the valve of the filling plug. The refrigerant then passes along the liquid line to the evaporator.

The evaporator consisted of 15mm Cu tubes wrapped around the edge of an insulated 32 liter SS bath well. The bath was filled with a 50: 50 glycol: aqueous solution and heat was supplied by a 3X 1kW heater controlled by a PID controller. The large blade agitator ensures even heat distribution. The evaporation pressure is controlled by an automatic expansion valve.

The refrigerant vapor is returned to the compressor through the suction line heat exchanger.

The Dasylab was used to automatically record all 12 temperature readings, 5 pressure readings, compressor power and heat input.

The test was carried out at a condensation temperature of 40 ℃ and an evaporator superheated to 8 ℃ (± 0.5 ℃).

The temperature at the end of the evaporator was maintained at 8 c above the temperature corresponding to the evaporation pressure for R22.

The temperature at the end of the evaporator is maintained at a temperature of 8 c, corresponding to a temperature above the evaporation pressure (dew point), for the other refrigerants.

The average evaporator temperature (ev. temp) of the refrigerant is calculated as follows: the temperature corresponding to the evaporator pressure from the bubble point table is added to the half slip temperature at that temperature.

The pressure was set roughly initially and then the temperature of the bath was set. The pressure was then adjusted to ensure a superheat of 8 c, measured at the outlet of the third evaporator. No adjustments are made during operation, except that the valve at the compressor outlet may be changed slightly to keep conditions as stable as possible. The test was continued for at least 1 hour, during which 6 readings were taken, i.e. recorded every ten minutes. If the readings are stable, the average is calculated.

Specific test details for each refrigerant

The refrigerants are given in the order, and the measurement is performed in the order.

R22: r22(3.477kg) was added to the liquid receiver, since the LT calorimeter was used for the first time, the main base data needed to be modified for R22. Thus 8 data points were obtained between the evaporation temperature-33 ℃ and-21 ℃.

75% of R125: about 3.54kg was added to the liquid receiver, and 4 data points were obtained between the average evaporation temperature of-31 c and-23 c, respectively, and the expansion valve was fully opened at the average evaporation temperature of-23 c.

85% of R125: about 3.55kg was added to the liquid receiver, 4 data points were obtained between-31 ℃ and-25 ℃ average evaporation temperature, and the expansion valve was fully opened at-26 ℃ average evaporation temperature.

85% R125(R600 a): approximately 3.56kg was added to the liquid receiver and 5 data points were obtained between the average evaporation temperature-44.5 ℃ and-28 ℃.

R407C: approximately 3.59kg was added to the liquid receiver and 5 data points were obtained between the average evaporation temperature-32 ℃ and-20 ℃.

70% of R125: approximately 3.5kg was added to the liquid receiver and 5 data points were obtained between the average evaporation temperature-32 ℃ and-21 ℃.

R404A: approximately 3.51kg was added to the liquid receiver and 5 data points were obtained between the average evaporation temperature-33 ℃ and-25 ℃.

Results

The results obtained are listed in tables 3-8, average ev. Air on the condenser, which is the air temperature at room temperature, was blown through an air-cooled condenser, measured just before the air was blown through the condenser; press is pressure.

Description and discussion of test results

Figure 1 shows a comparison of the (refrigeration) capacity at an average evaporation temperature of-30 c and R404A. This evaporation temperature is considered to be the temperature at which operation of the cryogenic refrigerant is expected to be typical. It can be seen that 85% of R125 and 85% of R125(R600a) have relatively slightly better capacity than R404A, while other tested refrigerants have poorer capacity, with R22 and 75% of R125 being the next best. At this temperature R407C is the least good, but relatively improved as the average evaporation temperature increases. Generally, the refrigeration capacity improves with increasing R125 content.

Figure 2 shows the COP results obtained, indicating that 85% R125 and 85% R125(R600a) give the best efficiency at-30 ℃, being the only refrigerant better than R404A.

Figures 3 and 4 show the capacity and COP for any given refrigerant relative to R22, again indicating the similarity of 85% R125 and 85% R125(R600a) to R404A, all exceeding R225-10% and above.

Thus the preferred formulations are 85% R125 and 85% R125(R600 a). Assuming that n-butane and isobutane have the same GWP as methane (21), it is 22% lower than R404a and 23% lower than R507.

Preferred compositions are 85% w/w R125, 11.5% w/w R134a and 3.5% w/w butane or isobutane which have a vapour pressure/temperature relationship very close to that of R404A, for example the vapour pressure of the R404A liquid is 0.209MPa (30.3psia) at-30 ℃ and preferred compositions have a vapour pressure for butanes which is higher than 0.218MPa (31.6psi) for the liquid and 0.223MPa (32.3psia) for isobutane, i.e. only 4-6% higher.

Table 1 details of test refrigerants

Description of the invention	Composition comprising a metal oxide and a metal oxide
		70％R125	R125/134a/600(70.0/26.5/3.5)
75％R125	R125/134a/600(75.0/21.5/3.5)
		85％R125	R125/134a/600(85.0/11.5/3.5)
85％R125(R600a)	R125/134a/600a(85.0/11.5/3.5)
		R407C	R32/125/134a(23.0/24.0/52.0)
R404A	R125/143a/134a(44.1/51.9/4.0)

TABLE 2 Experimental SVP assay results and glide from REFPRUP6

Description of the invention	SVP equation (see note 1)	Slip equation (see note 2)
			70％R125	y＝-2357.53678x+13.02249	y＝-0.02391x+3.22225R2＝0.99786
75％R125	y＝-2318.71536x+12.93301R2＝1.00000	y＝-0.02122x+2.84478R2＝0.99704
			85％R125	y＝-2318.35322x+12.98687R2＝0.99998	y＝-0.01305x+1.85013R2＝0.99456
85％R125(R600a)	y＝-2307.282362x+12.964359R2＝0.999973	y＝-0.0157x+1.7337R2＝0.998
			R407C(3)	y＝-2422.08237x+13.27060	y＝-0.000118x2-0.027343x+6.128020R2＝0.998575
R404A	y＝-2367.62611x+13.14935R2＝0.99994	y＝-0.005014x+0.547125R2＝0.995941
			R22	(see note 4)	Is not applicable

And annotating:

(1) where x is 1/T, where T is the bubble point (K): y ═ 1n (p), where p is the saturated vapor pressure (psia).

(2) In this formula, x is t, where t is the liquid temperature (c) (bubble point) and y is glide (c) (at the bubble point temperature).

(3) The data used are from Refprop, but are consistent with the data of the Ashrae manual and ICI.

(4) The vapor pressure of R22 was obtained by interpolation from the Ashrae handbook.

TABLE 3 condensation of R22 at 40 ℃ in a Low temperature calorimeter
												Mean evaporation temperature	Discharge temperature	Air in condenser	Discharge absolute pressure (MPa)	Condensation temperature	Absolute inlet pressure (MPa) of evaporator	Evaporation temperature bubble point	Dew point of evaporation temperature	Compressor power kwh	Refrigerating capacity (Heat input kwh)	C.O.P.	Evaporative superheating
												-33.0	159.5	24.2	1.532	40.0	0.144	-33.0	-33.0	1.339	1.224	0.91	8.5
-30.2	153.1	18.9	1.545	40.3	0.163	-30.2	-30.2	1.412	1.367	0.97	8.5
												-27.8	152.4	20.6	1.538	40.1	0.180	-27.8	-27.8	1.486	1.653	1.11	8.5
-27.5	156.6	24.4	1.516	39.5	0.182	-27.5	-27.5	1.482	1.704	1.15	7.7
												-25.4	155.6	24.3	1.547	40.4	0.199	-25.4	-25.4	1.606	2.020	1.26	8.4
-25.0	155.2	24.2	1.538	40.1	0.205	-25.0	-25.0	1.660	2.139	1.29	8.8
												-22.5	154.5	26.3	1.551	40.5	0.223	-22.5	-22.5	1.686	2.323	1.38	7.9
-20.7	150.5	24.7	1.555	40.6	0.238	-20.7	-20.7	1.729	2.526	1.46	8.1

Note: all temperatures are expressed in DEG C

TABLE 470% condensation of R125 (69.98% R125/26.51% R134 a/3.51% R600) at 40 ℃ with a low temperature calorimeter (ITS 7694)
												Mean evaporation temperature	Discharge temperature	Air in condenser	Discharge absolute pressure (MPa)	Condensation temperature	Absolute inlet pressure (MPa) of evaporator	Evaporation temperature bubble point	Dew point of evaporation temperature	Compressor power kwh	Refrigerating capacity (Heat input kwh)	C.O.P.	Evaporative superheating
												-32.4	117.7	23.4	1.697	40.5	0.160	-34.4	-30.4	1.302	1.148	0.88	8.3
-29.6	115.6	24.8	1.690	40.3	0.180	-31.6	-27.6	1.384	1.389	1.00	7.9
												-26.1	108.8	21.2	1.686	40.2	0.207	-28.1	-24.2	1.499	1.768	1.18	8.0
-23.5	108.1	23.4	1.691	40.3	0.230	-25.4	-21.6	1.589	2.046	1.29	8.2
												-21.5	107.3	24.4	1.691	40.3	0.248	-23.4	-19.6	1.657	2.260	1.36	8.0

Note: all temperatures are expressed in DEG C

TABLE 575 condensation of R125 (75.02% R125/21.48% R134 a/3.50% R600) at 40 ℃ in a low temperature calorimeter (ITS 7616)
												Mean evaporation temperature	Discharge temperature	Air in condenser	Discharge absolute pressure (MPa)	Condensation temperature	Absolute inlet pressure (MPa) of evaporator	Evaporation temperature bubble point	Dew point of evaporation temperature	Compressor power kwh	Refrigerating capacity (Heat input kwh)	C.O.P.	Evaporative superheating
												-30.7	115.2	25.0	1.736	40.0	0.187	-32.4	-28.9	1.421	1.403	0.99	8.1
-27.8	112.4	25.7	1.746	40.3	0.210	-29.5	-26.0	1.476	1.644	1.11	7.7
												-25.0	110.9	28.1	1.733	39.9	0.234	-26.7	-23.3	1.610	1.981	1.23	7.6
-23.3	108.0	26.7	1.731	39.9	0.250	-25.0	-21.6	1.653	2.190	1.33	7.6

Note: all temperatures are expressed in DEG C

TABLE 685% condensation of R125 (85.05% R125/11.45% R134 a/3.50% R600) at 40 ℃ with a low temperature calorimeter (ITS 7677)
												Mean evaporation temperature	Discharge temperature	Air in condenser	Discharge absolute pressure (MPa)	Condensation temperature	Absolute inlet pressure (MPa) of evaporator	Evaporation temperature bubble point	Dew point of evaporation temperature	Compressor power kwh	Refrigerating capacity (Heat wh)	C.O.P.	Evaporative superheating
												-31.4	109.3	20.3	1.839	40.1	0.197	-32.6	-30.3	1.462	1.501	1.03	8.1
-28.7	109.8	22.6	1.844	40.2	0.219	-29.8	-27.6	1.567	1.724	1.10	8.4
												-26.6	107.2	23.1	1.823	39.7	0.238	-27.7	-25.5	1.626	1.970	1.21	7.8
-25.2	103.9	20.4	1.845	40.2	0.251	-26.3	-24.1	1.688	2.190	1.30	8.2

Note: all temperatures are expressed in DEG C

TABLE 7 condensation of R407C (23.02% R32/25.04% R125/51.94% R134a) at 40 ℃ with a low temperature calorimeter (ITS 7361)
												Mean evaporation temperature	Discharge temperature	Air in condenser	Discharge absolute pressure (MPa)	Condensation temperature	Absolute inlet pressure (MPa) of evaporator	Evaporation temperature bubble point	Dew point of evaporation temperature	Compressor power kwh	Refrigerating capacity (Heat input kwh)	C.O.P.	Evaporative superheating
												-32.4	135.3	19.8	1.735	39.7	0.147	-35.9	-28.9	1.287	0.974	0.76	7.6
-29.4	133.8	18.9	1.738	39.7	0.167	-32.9	-26.0	1.428	1.405	0.98	7.7
												-25.7	132.4	20.1	1.746	39.9	0.196	-29.1	-22.3	1.499	1.736	1.16	7.8
-23.0	130.8	20.8	1.733	39.6	0.218	-26.4	-19.6	1.650	2.190	1.33	7.6
												-19.6	129.0	22.5	1.761	40.3	0.250	-22.9	-16.2	1.774	2.649	1.49	8.0

Note: all temperatures are expressed in DEG C

TABLE 8R 404A (44% R125/52% R143 a/4% R134a)
												Condensation at 40 ℃ with a Low temperature calorimeter (ITS 7726)
Mean evaporation temperature	Discharge temperature	Air in condenser	Discharge absolute pressure (MPa)	Condensation temperature	Absolute inlet pressure (MPa) of evaporator	Evaporation temperature bubble point	Dew point of evaporation temperature	Compressor power kwh	Refrigerating capacity (Heat input kwh)	C.O.P.	Evaporative superheating
-33.0	123.4	23.7	1.831	39.7	0.182	-33.4	-32.7	1.405	1.291	0.92	8.0
												-31.2	120.5	23.1	1.829	39.7	0.196	-31.5	-30.8	1.472	1.473	1.00	7.6
-29.6	118.1	22.8	1.824	39.6	0.210	-29.9	-29.2	1.522	1.624	1.07	7.7
												-26.9	118.2	25.1	1.850	40.1	0.233	-27.3	-26.6	1.641	1.910	1.16	8.1
-24.7	112.6	21.4	1.865	40.5	0.254	-25.0	-24.3	1.740	2.272	1.31	8.1

Note: all temperatures are expressed in DEG C

TABLE 985% R125(R600a) (85% R125/11.45% R134 a/3.50% R600a)
												Condensation at 40 ℃ in a low-temperature calorimeter
Mean evaporation temperature	Discharge temperature	Air in condenser	Discharge pressure (psig)	Condensation temperature	Evaporator inlet pressure (psig)	Evaporation temperature bubble point	Dew point of evaporation temperature	Compressor power kwh	Refrigerating capacity (kW)	C.O.P.	Evaporative superheating
-44.5	115.4	24.5	256.0	40.2	2.0	-45.8	-43.3	1.022	0.313	0.31	8.5
												-39.9	116.6	24.6	254.7	40.0	5.8	-41.1	-38.7	1.137	0.623	0.55	7.9
-36.2	114.2	21.8	254.2	39.9	9.3	-37.3	-35.0	1.319	1.025	0.78	8.3
												-31.8	107.4	19.1	251.6	39.5	14.1	-32.9	-30.7	1.462	1.482	1.01	8.5
-28.0	106.5	20.8	254.0	39.9	18.8	-29.1	-26.9	1.605	1.827	1.14	8.3
												-24.0	101.8	19.7	253.5	39.8	24.4	-25.0	-22.9	1.763	2.336	1.33	7.9

Claims (23)

1. A refrigerant composition comprising:

(a) pentafluoroethane, trifluoromethoxydifluoromethane or hexafluoro-cyclopropane, or a mixture of two or more thereof, in an amount of at least 75% based on the weight of the composition,

(b)1, 1, 1, 2-or 1, 1, 2, 2-tetrafluoroethane, trifluoromethoxy pentafluoroethane, 1, 1, 1, 2, 3, 3-heptafluoropropane or a mixture of two or more thereof in an amount of from 5 to 24% by weight, based on the weight of the composition, and

(c) an ethylenically unsaturated or saturated hydrocarbon, optionally containing one or several oxygen atoms, having a boiling point of from-50 ℃ to +35 ℃, or mixtures thereof, in an amount of from 1% to 4% by weight, based on the weight of the composition, the weight ratio of component (a) to component (b) being at least 3: 1.

2. The composition of claim 1 wherein component (c) is present in an amount of 3 to 4 weight percent based on the weight of the composition.

3. The composition of claim 2 wherein the amount of component (c) is about 3.5% by weight based on the weight of the composition.

4. A composition according to any one of claims 1 to 3, wherein component (c) is one or more of propane, n-butane, isobutane, cyclobutane, cyclopropane, methylcyclopropane, pentane, isobutane, dimethyl ether, ethyl methyl ether, propylene and oxetane.

5. The composition of claim 4 wherein component (c) is n-butane and/or isobutane.

6. The composition of any preceding claim wherein (a) is present as pentafluoroethane.

7. The composition of any of the preceding claims wherein component (a) is present in an amount of from 80 to 90 weight percent based on the weight of the composition.

8. The composition of claim 7 wherein the amount of component (a) is from 83 to 88 weight percent based on the weight of the composition.

9. A composition according to any preceding claim wherein component (b) is 1, 1, 1, 2-tetrafluoroethane.

10. A composition according to any preceding claim wherein component (b) is present in an amount of from 10 to 15% by weight based on the weight of the composition.

11. A composition according to any preceding claim, wherein the weight ratio of component (a) to component (b) is from 5: 1 to 10: 1.

12. The composition of claim 11, wherein said weight ratio is 7: 1 to 9: 1.

13. The composition of any of the preceding claims, further comprising additional components.

14. The composition of claim 13 wherein the other component is a hydrofluorocarbon.

15. The composition of claim 14 wherein the hydrofluorocarbon has a boiling point at atmospheric pressure of up to-40 ℃.

16. The composition of claim 14 or 15, wherein the F/H ratio in the hydrofluorocarbon is at least 1.

17. The composition of claim 16, wherein the hydrofluorocarbon is difluoromethane or trifluoromethane.

18. A composition according to any one of the preceding claims 13 to 17 wherein the other components are present in an amount of not more than 5% by weight based on the weight of (a), (b) and (c).

19. The composition of claim 18 wherein the other components are present in an amount of no more than 2% by weight based on the weight of (a), (b) and (c).

20. A composition according to claim 1 substantially as hereinbefore defined.

21. Use of a composition according to any preceding claim as a refrigerant in a refrigeration appliance.

22. A method of producing refrigeration comprising condensing a composition according to any one of claims 1 to 20 and thereafter evaporating the composition in the vicinity of a body portion in need of cooling.

23. A refrigeration device comprising as a refrigerant the composition of any one of claims 1 to 20.