Working fluids comprising fluorinated olefins and polyol esters

1. A working fluid comprising:

i) a fluorinated olefin refrigerant, and

ii) a polyol ester lubricant composition having a kinematic viscosity at 40° C. of from 150 to 360 cSt, which polyol ester lubricant composition comprises:

a) from 25 to 40 wt % C 5-12 alkylcarboxy esters of mono-pentaerythritol,

b) from 15 to 25 wt % C 5-12 alkylcarboxy esters of di-pentaerythritol, and

c) from 40 to 55 wt % C 5-12 alkylcarboxy esters of tri-pentaerythritol and higher pentaerythritol oligomers,

wherein from 55 to 100 mol % of the alkylcarboxy groups are selected from C 7-10 alkylcarboxy, and from 50 to 80 mol % of all alkylcarboxy groups are branched.

2. The working fluid according to claim 1 wherein 70 to 100 mol % of the alkylcarboxy groups are selected from C 7-10 alkylcarboxy.

3. The working fluid according to claim 1 wherein 55 to 80 mol % of the alkylcarboxy groups are branched.

4. The working fluid according to claim 1 wherein from 28 to 39 wt % of the polyol ester lubricant composition consists of alkylcarboxy esters of mono-pentaerythritol.

5. The working fluid according to claim 1 wherein the polyol ester lubricant composition comprises:

a) from 28 to 40 wt % C 5-12 alkylcarboxy esters of mono-pentaerythritol,

b) from 16 to 24 wt % C 5-12 alkylcarboxy esters of di-pentaerythritol, and

c) from 42 to 54 wt % C 5-12 wt % alkylcarboxy esters of tri-pentaerythritol and higher pentaerythritol oligomers.

6. The working fluid according to claim 1 wherein 51 to 100% of the branched alkylcarboxy groups are 3,5,5-trimethylhexanoyl or 2,2,4,4-tetramethylbutanoyl.

7. The working fluid according to claim 1 wherein the polyol ester lubricant composition has a kinematic viscosity at 40° C. of at least 160 cSt.

8. The working fluid according to claim 1 wherein the polyol ester lubricant composition has a kinematic viscosity at 40° C. of from 194 to 340 cSt.

9. The working fluid according to claim 1 wherein fluorinated olefin refrigerant comprises a hydrofluoro- or perfluoro-olefin of from 2 to 7 carbon atoms.

10. The working fluid according to claim 9 wherein the hydrofluoro- or perfluoro-olefin contains three or more fluorine atoms.

11. The working fluid according to claim 10 wherein the hydrofluoro- or perfluoro-olefin contains four or more fluorine atoms.

12. The working fluid according to claim 10 wherein the hydrofluoro- or perfluoro-olefin comprises a pentafluoro-, tetrafluoro-, or trifluoro-propene isomer.

13. The working fluid according to claim 1 wherein fluorinated olefin refrigerant comprises a tetrafluoro-propene isomer.

14. The working fluid according to claim 1 wherein the fluorinated olefin refrigerant consists of hydrofluoro-olefins or perfluo-olefins.

15. The working fluid according to claim 1 wherein the fluorinated olefin refrigerant is a mixture comprising a hydrofluoro-olefin and/or perfluo-olefin, and a hydrocarbon, fluorinated alkyne, hydrofluoro-alkane and/or perfluoroalkane refrigerant.

16. The working fluid according to claim 15 wherein the fluorinated olefin refrigerant is a mixture comprising a hydrofluoro-olefin and a hydrofluoro-alkane.