WO1993015163A1

WO1993015163A1 - Novel refrigerant compositions

Info

Publication number: WO1993015163A1
Application number: PCT/US1993/000862
Authority: WO
Inventors: Daniel Franklin Harnish; Earl August Eugene Lund; Ian Robert Shankland; Rajiv Ratna Singh; David Paul Wilson
Original assignee: Allied-Signal Inc.
Priority date: 1992-02-03
Filing date: 1993-02-02
Publication date: 1993-08-05
Also published as: AU3602193A; CN1076713A

Abstract

Compositions comprising 1,1,1,2-tetrafluoroethane, pentafluoroethane and a member selected from the group consisting of 1,1-difluoroethane, propane and trifluoromethane, having a vapor pressure from about 12.2 psia to about 18.4 psia at -40 °F.

Description

NOVEL REFRIGERANT COMPOSITIONS

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BACKGROUND OF THE INVENTION

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

10

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 15 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

20 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.

25

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

30 considered to be environmentally acceptable substitutes for the presently used chlorofluorocarbons. The latter, such as monochlorodifluoromethane (HCFC-22) are suspected of causing environmental problems in connection with the earth's protective ozone layer.

35 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. 5

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

10 refrigeration cycle has to be redesigned, see for example T. Atwood "NARBs - The Promise and the Problem", paper 86-WA/Ht-61 American Society of Mechanical Engineers. In most existing designs of refrigeration equipment, a temperature glide is a cause

15 of concern. Therefore non-azeotropic refrigerant mixtures have not found wide use. An environmentally acceptable non-azeotropic mixture with a small temperature glide and with a similar refrigeration capacity to other known pure fluids, such as HCFC-22

20 would advance the art.

1,1,1,2-Tetrafluoroethane (HFC-134a) is considered to be an environmentally acceptable refrigerant but it is much less volatile than HCFC-22 and consequently

25 offers a much lower refrigeration capacity than HCFC- 22. Use of HFC-134a as an alternative for HCFC-22 would require significant and costly equipment redesign. Moreover, at lower evaporating temperatures, HFC-134a exhibits a subatmospheric vapor pressure.

30 System leaks would result in an influx of air causing performance and reliability deterioration. ,

Pentafluoroethane (HFC-125) is also considered to be an environmentally acceptable refrigerant. However, 35 its critical temperature is very low, about 54°F lower than that of HCFC-22. Because of this low critical temperature, the refrigeration capacity of HFC-125 drops at high condensing temperatures and a system using HFC-125 becomes very inefficient.

1,1-Difluoroethane (HFC-152a) and propane are environmentally acceptable fluid but are very flammable.

Trifluoromethane (HFC-23) is also environmentally acceptable but has a room temperature critical point making it impractical in any HCFC-22 application.

DESCRIPTION OF THE INVENTION

In accordance with the invention, novel non- azeotropic compositions have been discovered comprising HFC-134a, HFC-125 and a member selected from the group consisting of HFC-152a, propane and HFC-23, having a vapor pressure of about 12.2 psia to about 18.4 psia at -40^βF.

When the selected member is HFC-152a, the compositions comprise from about 15 to about 70 mole percent HFC-134a, from about 30 to about 85 mole percent HFC-125 and from about 1 to about 35 mole percent HFC-152a. The preferred compositions are from about 20 to about 45 mole percent HFC-134a, from about 40 to about 70 mole percent HFC-125 and from about 2 to about 25 mole percent HFC-152a.

When the selected member is propane, the compositions comprise from about 15 to about 70 mole percent HFC-134a, from about 30 to about 85 mole percent HFC-125 and from about 1 to about 12 mole percent propane. The preferred compositions are from about 20 to about 45 mole percent HFC-134a, from about 40 to about 70 mole percent HFC-125 and from about 2 to i about 10 mole percent propane.

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When the selected member is HFC-23, the compositions comprise from about 30 to about 95 mole percent HFC-134a, from about 1 to about 75 mole percent HFC-125 and from about 1 to about 10 mole percent HFC- 10 23. The preferred compositions are from about 40 to about 80 mole percent HFC-134a, from about 40 to about 60 mole percent HFC-125 and from about 2 to about 5 mole percent HFC-23.

15 The HFC-134a, HFC-125, HFC-152a, propane and HFC- 23 components of the novel compositions of the invention are all known materials and are either commercially available or may be prepared by known methods. Preferably they should be used in

20 sufficiently high purity so as to avoid the intro¬ duction of adverse influences upon the properties of the system.

Additional components may be added to the 25 compositions to tailor the properties according to the need, for example, additional refrigeration components, hydrocarbons to aid oil solubility if not already present and additives, such as lubricants.

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The novel compositions of the invention satisfy the above-identified objectives for being a replacement for HCFC-22. The compositions are generally non¬ flammable; however, certain compositions within the 35 broad scope of the invention may be flammable and may be avoided if desired. Flammability may readily be measured by an ASTM E-681 apparatus. Calculation of the thermodynamic properties of these compositions show that the refrigeration performance is substantially the same as that of HCFC-22.

In addition to having zero ozone depletion potential and providing a good match for the capacity of HCFC-22, the novel compositions of the invention provide the additional advantages of having a higher critical temperature than that of HFC-125. The higher critical temperature translates to improved energy efficiency in a refrigeration or air conditioning cycle, especially at high condensing temperatures. The temperature glide that occurs on evaporation and condensation with non-azeotropic refrigerants is smaller for the compositions containing propane than for the binary combination of HFC-134a and HFC-125 disclosed in the prior art.

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. K vamp l a 1

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 a 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.

Theoretical performance calculations for an air conditioning refrigeration cycle where the average temperature is typically 115"F and where the average evaporator temperature is typically 40°F are performed using these standard techniques. Isentropic compression and a compressor inlet temperature of 60°F are assumed. Calculations show that blends of the current invention match the capacity of HCFC-22, offer very similar COPs (Coefficient of Performance) and exhibit discharge temperatures significantly lower than HCFC-22. The temperature glide is determined not to exceed 11"F which is minor. 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 6 to 7^βF are minor. The temperature glide here is 9 to ll'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.

Claims

W claim:

1. Compositions comprising 1,1,1,2-tetrafluoroethane, pentafluoroethane and a member selected from the group consisting of 1,1-difluoroethane, propane and trifluoromethane, having a vapor pressure from about 12.2 psia to about 18.4 psia at -40"F.

2. Compositions according to claim 1 consisting essentially of the components recited.

3. Compositions according to claim 1 comprising from about 15 to about 70 mole percent 1,1,1,2-tetra- fluoroethane, from about 30 to about 85 mole percent pentafluoroethane and from about 1 to about 35 mole percent 1,1-difluoroethane.

4. Compositions according to claim 3 comprising from about 20 to about 45 mole percent 1,1,1,2-tetra- fluoroethane, from about 40 to about 70 mole percent pentafluoroethane and from about 2 to about 25 mole percent 1,1-difluoroethane.

5. Compositions according to claim 1 comprising from about 15 to about 70 mole percent 1,1,1,2-tetra- fluoroethane, from about 30 to about 85 mole percent pentafluoroethane and from about 1 to about 12 mole percent propane.

6. Compositions according to claim 5 comprising from about 20 to about 45 mole percent 1,1,1,2-tetra- fluoroethane, from about 40 to about 70 mole percent pentafluoroethane and from about 2 to about 10 mole percent propane.

7. Compositions according to claim 1 comprising from about 30 to about 95 mole percent 1,1,1,2-tetra- fluoroethane, from about 1 to about 75 mole percent pentafluoroethane and from about 1 to about 10 mole percent trifluoromethane.

8. Compositions according to claim 7 comprising from about 40 to about 80 mole percent 1,1,1,2-tetra- fluoroethane, from about 40 to about 60 mole percent pentafluoroethane and from about 2 to about 5 mole percent trifluoromethane.

9. The method for producing refrigeration which comprising condensing a composition of claim 1 and thereafter evaporating the composition in the vicinity of a body to be cooled.

10. The method for producing heating which comprises condensing a composition of claim 1 in the vicinity of a body to be heated and thereafter evaporating said composition.