Compositions – Vaporization – or expansion – refrigeration or heat or energy... – With lubricants – or warning – stabilizing or anti-corrosion...
Reexamination Certificate
1997-11-24
2001-06-12
Ogden, Necholus (Department: 1751)
Compositions
Vaporization, or expansion, refrigeration or heat or energy...
With lubricants, or warning, stabilizing or anti-corrosion...
C252S067000, C252S073000
Reexamination Certificate
active
06245254
ABSTRACT:
The present invention relates generally to lubricants and more particularly to working fluid compositions contained in heat transfer devices which comprise the lubricant and a heat transfer fluid.
Heat transfer devices of the mechanical compression type such as those used in refrigerators, freezers, heat pumps and automobile air conditioning systems are well known. In such devices a heat transfer fluid of a suitable boiling point evaporates at low pressure taking heat from a surrounding zone. The resulting vapour is then compressed and passes to a condenser where it condenses and gives off heat to a second zone. The condensate is then returned through an expansion valve to the evaporator so completing the cycle. The mechanical energy required for compressing the vapour and pumping the fluid is provided by, for example, an electric motor or an internal combustion engine.
The heat transfer fluids used in these heat transfer devices include chlorine containing fluoroalkanes such as dichlorodifluoromethane (R-12), chlorodifluoromethane (R-22) and mixtures thereof with, for example, fluoroalkanes such as 1,1-difluoroethane (R-152a). However, such chlorine containing fluoroalkanes have been implicated in the destruction of the ozone layer and as a result the use and production thereof is to be severely limited by international agreement. The use of certain fluoroalkanes and hydrofluoroalkanes in place of the chlorine containing fluoroalkanes has been proposed. The fluoroal-kanes and hydrofluoroalkanes of particular interest are those compounds which have comparable boiling points and other thermal properties to the chlorine containing fluoroalkanes which they are replacing, but which are also less damaging or benign to the ozone layer. Thus, R-12 is generally being replaced by a new refrigerant, 1,1,1,2-tetrafluoroethane (R-134a).
Hitherto, heat transfer devices have tended to use mineral oils as lubricants. The good solubility of chlorine containing fluoroalkanes with mineral oils allows the mineral oil to circulate around the heat transfer device together with the chlorine containing fluoroalkane, and this in turn ensures proper lubrication of the compressor. Unfortunately, however, the replacement fluoroalkane and hydrofluoroalkane heat transfer fluids such as R-134a have different solubility characteristics to the chlorine containing fluoroalkanes presently in use and tend to be insufficiently soluble in mineral oils to allow the latter to be used as lubricants. Consequently, numerous alternative lubricants such as polyoxyalkylene glycols terminating in hydroxyl and other groups, esters of polyols with mono- and polyfunctional acids, and halo substituted esters and ethers have been proposed as lubricants for use with the replacement heat transfer fluids.
Unfortunately, R-134a cannot be used as a direct replacement for certain of the refrigerants which are presently in use such as R-22 and R-502 (an azeotropic mixture of R-22 and chloropentafluoroethane R-115) since it does not possess comparable boiling characteristics and thermal properties. It has thus been proposed that existing refrigerants such as R-22 and R-502 be replaced by refrigerant mixtures comprising two or more refrigerants selected from the fluoroalkanes and hydrofluoroalkanes. Particular mention may be made of binary mixtures of refrigerants such as R-134a and difluoromethane (R-32) or R-32 and pentafluoroethane (R-125). Unfortunately, these refrigerant mixtures are also not sufficiently soluble in mineral oils to allow the latter to be used as lubricants. Moreover, the miscibility and solubility of an alternative lubricant with one component of the mixture, for example with R-134a, does not mean that such a lubricant will also be miscible and soluble with the refrigerant mixture itself. In consequence, the development of a lubricant which exhibits acceptable lubricating properties in a heat transfer device utilising a refrigerant mixture presents a very real problem.
It has now been found that if a prospective lubricant is at least partially soluble in each component of the refrigerant mixture then it will be at least partially soluble in the refrigerant mixture itself, thereby enabling its use as a lubricant with that mixture. Such a lubricant may provide an acceptable lubricating action even if it is immiscible with one or more of the components of the refrigerant mixture or with the refrigerant mixture itself.
According to the present invention there is provided a working fluid composition comprising
(A) a heat transfer fluid comprising a mixture of at least two compounds selected from the group consisting of hydrofluoroalkanes and fluoroalkanes; and
(B) sufficient to provide lubrication of a lubricant which is at least partially soluble in each component of the heat transfer fluid.
The heat transfer fluid may comprise two, three or more components. Preferred hydrofluoroalkanes and fluoroalkanes are selected from the group consisting of difluoromethane (R-32), 1,1,2,2-tetrafluoroethane (R-134), 1,1,1,2-tetrafluoroethane (R-134a), pentafluoroethane (R-125), 1,1-difluoroethane (R-152a), 1,1,1-trifluoroethane (R-143a) and 1,1,2-trifluoroethane (R-143).
One suitable heat transfer fluid comprises a mixture of R-32 and R-125. Such a mixture may comprise equal proportions of each component on a weight basis.
The present invention is particularly concerned with the provision of a working fluid composition which provides a useful replacement for the working fluids presently in use which comprise R-22 or R-502 as the refrigerant and a mineral oil lubricant. A particularly desirable working fluid composition in this respect is one which comprises
(A) a heat transfer fluid comprising a mixture of:
(1) tetrafluoroethane;
(2) at least one hydrofluoroalkane selected from the group consisting of difluoromethane (R-32) and 1,1,1-trifluoroethane (R-143a); and optionally (3) pentafluoroethane (R-125); and
(B) sufficient to provide lubrication of a lubricant which is at least partially soluble in each component of the heat transfer fluid.
The tetrafluoroethane may be 1,1,1,2-tetrafluoroethane (R-134a) or 1,1,2,2-tetrafluoroethane (R-134) or a mixture of these two isomers. Preferably, however, the tetrafluoroethane is a single isomer, and more preferably is R-134a.
Although the heat transfer fluid may comprise more than three components, it is preferably a binary or ternary mixture. The mixture may be an azeotrope or near-azeotrope, but will normally be zeotropic.
In one preferred embodiment of the present invention, the heat transfer fluid is a binary mixture consisting essentially of R-134a and R-32. Such a mixture provides a particularly suitable replacement for the R-22 refrigerant which has been used hitherto in commercial refrigeration systems and related heat transfer devices. Preferably, such a mixture comprises from 45 to 75% by weight, more preferably from 65 to 75% by weight of R-134a and from 25 to 55% by weight, more preferably from 25 to 35% by weight of R-32. A particularly preferred binary mixture comprises about 70% by weight of R-134a and about 30% by weight of R-32.
In a further preferred embodiment of the present invention, the heat transfer fluid comprises a ternary or higher mixture of:
(1) R-134a or R-134;
(2) at least one hydrofluoroalkane selected from the group consisting of R-32 and R-143a; and optionally (3) R-125.
Such a heat transfer fluid provides a suitable replacement for the R-22 and R-502 refrigerants which have been used hitherto in commercial refrigeration systems and related heat transfer devices.
Particularly suitable ternary heat transfer fluids may be selected from:
(a) R-134a+R-32+R-143a;
(b) R-134+R-32 +R-143a;
(c) R-134a+R-32 +R-125;
(d) R-134+R-32 +R-125;
(e) R-134a+R-143a +R-125; and
(f) R-134+R-143a+R-125.
A particularly preferred heat transfer fluid comprises a mixture of:
(1) R-134a or R-134, especially R-134a;
(2) R-32 or R-143a, especially R-32; and
(3) R-125.
Such heat transfer fluids provide a particularly suitable re
Imperial Chemical Industries plc
Ogden Necholus
Pillsbury & Winthrop LLP
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