BACKGROUND OP THE INVENTION

Fluorocarbon based fluids have found widespread use in industry for refrigeration, air conditioning and heat pump applications.

Vapor compression cycles are one common form of refrigeration. In its simplest form, the vapor compression cycle involves changing the refrigerant from the liquid to the vapor phase through heat absorption at a low pressure, and then from the vapor to the liquid phase through heat removal at an elevated pressure.

While the primary purpose of refrigeration is to remove energy at low temperature, the primary purpose of a heat pump is to add energy at higher temperature. Heat pumps are considered reverse cycle systems because for heating, the operation of the condenser is inter¬ changed with that of the refrigeration evaporator.

The art is continually seeking new fluorocarbon based fluids which offer alternatives for refrigeration and heat pump applications. Currently, of particular interest, are fluorocarbon based mixtures which are considered to be environmentally acceptable substitutes for the presently used chlorofluorocarbons. The latter, such as R-502 (an azeotropic blend of ^' 48.8 weight percent monochlorodifluoromethane and 51.2 weight percent onochloropentafluoroethane) are

suspected of causing environmental problems in connection with the earth's protective ozone layer.

The substitute materials must also possess those properties unique to the chlorofluorocarbons including similar refrigeration characteristics, chemical stability, low toxicity, non-flammability, efficiency in-use and low temperature glides.

By "similar refrigeration characteristics" is meant a vapor pressure which is plus or minus 20 percent of the reference refrigerant at the same temperature.

The characteristic of efficiency in-use is important, for example, in air conditioning and refrigeration where a loss in refrigerant thermodynamic performance or energy efficiency may have secondary environmental impacts through increased fossil fuel usage arising from an increased demand for electrical energy.

Low temperature glides have the following described significance. The condensation and evaporation temperatures of single component refrigerant fluids are defined clearly. If the small pressure drops in the refrigerant lines are ignored, the condensation or evaporation occurs at a single temperature corresponding to the condenser or evaporation pressure. For mixtures employed as refrigerants, there is no single phase change temperature but a range of temperatures. This range is governed by the vapor-liquid equilibrium behavior of the mixture. This property of mixtures is responsible for the fact that when non-azeotropic mixtures are used

in the refrigeration cycle, the temperature in the condenser or the evaporator has no longer a single uniform value, even if the pressure drop effect is ignored. Instead, the temperature varies across the equipment, regardless of the pressure drop. In the art this variation in the temperature across an equipment is known as temperature glide.

For non-isothermal heat sources and heat sinks, this temperature glide in mixtures can be utilized to provide better efficiencies. However in order to benefit from this effect, the conventional refrigeration cycle has to be redesigned, see for example T. Atwood "NARBs - The Promise and the Problem", paper 86-WA/Ht-6l American Society of

Mechanical Engineers. In most existing designs of refrigeration equipment, a temperature glide is a cause of concern. Therefore non-azeotropic refrigerant mixtures have not found wide use. An environmentally acceptable non-azeotropic mixture with a small temperature glide which remains nonflammable and has similar refrigeration characteristics to R-502 would advance the art.

Monochlorodifluoromethane (HCFC-22) is more environmentally acceptable than some of the presently used chlorofluorocarbons and has been used as a refrigerant commercially but is known in the art to have too high a discharge temperature for direct use in simple machines. Pentafluoroethane (HFC-125) is considered to be environmentally acceptable but is regarded as having too low a critical point. 1,1,1,2- Tetrafluoroethane (HFC-134a) is considered to be environmentally acceptable but has too high a boiling point to directly replace R-502.

DESCRIPTION OF THE INVENTION

In accordance with the invention, novel non- azeotropic compositions have been discovered comprising from about 1 to about 90 weight percent monochlorodi- fluoromethane (HCFC-22) , from about 1 to about 90 weight percent pentafluoroethane (HFC-125) and from about 1 to about 50 weight percent 1,1,1,2-tetra- fluoroethane (HFC-134a) . In preferred embodiments these compositions comprise from about 10 to about 80 weight percent HCFC-22, from about 10 to about 80 weight percent HFC-125 and from about 2 to about 4 weight percent HFC-134a. These compositions are non- azeotropic.

The HCFC-22, HFC-125 and HFC-134a components of the novel compositions of the invention are known materials. Preferably they should be used in sufficiently high purity so as to avoid the introduction of adverse influences upon the properties of the system.

Additional components may be added to the mixture to tailor the properties of the mixture according to the need. For example, in the art propane has been added to refrigerant compositions to aid oil solubility. Similar materials may be added to the present mixture.

The novel compositions of the invention satisfy the above-identified objectives for being a replacement for R-502. Calculation of the thermodynamic properties of these compositions show that the refrigeration performance is substantially the same as that of R-502. These compositions exhibit a vapor pressure

substantially the same as R-502 and retain this relationship even after substantial evaporation losses. Since all components of the claimed compositions are non-flammable, the claimed compositions are non- flammable and the leaking vapor as well as the remaining liquid are always non-flammable. Flammability may readily be measured by an ASTM E-681 apparatus.

In one process embodiment of the invention, the compositions of the invention may be used in a method for producing refrigeration which involves condensing a refrigerant comprising the compositions and thereafter evaporating the refrigerant in the vicinity of the body to be cooled.

In another process embodiment of the invention, the compositions of the invention may be used in a method for producing heating which involves condensing a refrigerant comprising the compositions in the vicinity of the body to be heated and thereafter evaporating the refrigerant.

The following examples show that a preferred composition within the scope of the invention has a refrigeration performance substantially the same as R- 502, yet is nonflammable even after substantial vapor leakage.

Example l

The theoretical performance of a refrigerant at specific operating conditions can be estimated from the thermodynamic properties of the refrigerant using standard refrigeration cycle analysis techniques, see

for example, "Fluorocarbons Refrigerants Handbook", Ch. 3, Prentice-Hall (1988) , by R.C. Downing. The coefficient of performance, COP, is a universally accepted measure, especially useful in representing the relative thermodynamic efficiency of a refrigerant in specific heating or cooling cycle involving evaporation or condensation of the refrigerant. In refrigeration engineering this term expresses the ratio of useful refrigeration to the energy applied by the compressor in compressing the vapor. The capacity of a refrigerant represents the volumetric efficiency of the refrigerant. To a compressor engineer this value expresses the capability of a compressor to pump quantities of heat for a given volumetric flow rate of refrigerant. In other words, given a specific compressor, a refrigerant with a higher capacity will deliver more cooling or heating power. A similar calculation can also be performed for non-azeotropic refrigerant blends.

We have performed this type of calculation for a typical air conditioning refrigeration cycle where the average condenser temperature is typically 110°F and the evaporator temperature is typically -407. We have further assumed isentropic compression and a compressor inlet temperature of 65"F. Such calculations were performed for a 37.2/55.8/7.0 percent by weight blend of HFC-22, HFC-125 and HFC-134a. The temperature glide in a typical R-502 application was determined not to exceed 3°F. The coefficient of performance (COP) , a measure of energy efficiency of the 37.2/55.8/7.0 blend is found to be 1.92 which is identical to the value found for R-502 under the same conditions. The refrigeration capacity for the blend was found to be 19700 BTU/hr. which is also identical to that of R-502.

According to the known art (D.A. Didion and D.B. Bivens "The role of Refrigerant Mixtures as Alternatives" in CFC's: Today's Options...Tomorrow's Solutions, NIST, 1990) temperature glides of the order of 4 to 5°F are minor. The temperature glide here is about 3°F.

Therefore the temperature glide of the compositions claimed herein is considered small in this art and need not pose a problem for conventional refrigeration units. The other refrigeration performance properties of the blend evaluated are compared with those of HCFC- 22 in the following Table.

Table

Example 2

It is shown here that a slow vapor leak in the system containing the non-azeotropic blend studied in Example 1 does not affect the refrigeration characteristics even if substantial amounts are lost. This is important for the servicing aspects of refrigeration machinery which may use this blend. The vapor pressure of the blend is 87 psia at 32°F which is within 5 percent of the vapor pressure of R-502. After 50 percent of the blend is lost by evaporation, the vapor pressure of the claimed blend becomes 84 psia, remaining within 2 percent of the vapor pressure of R- - 502. The efficiency or the COP remains same as that of R-502 and the refrigeration capacity decreases only marginally to 97 percent of the original capacity.