Patent ID: 8685271

Claim:
A working fluid for a heat transfer device comprising: i) a C 1-6 hydrocarbon refrigerant and ii) a polyol ester lubricant composition having a kinematic viscosity at 40Â° C. of 22-125 cSt, a viscosity index of greater than 140 and comprising a mixture of compounds of formula I wherein n is an integer of from 1 to 12, each R is independently an alkyl carbonyl of from 5 to 10 carbon atoms, each R 1 is independently selected and is either a group R or a substituent of formula II: wherein at least 80 molar % of all R groups are independently selected from straight chain alkylcarbonyls of from 7 to 10 carbon atoms, and wherein the polyol ester lubricant composition comprises a) from about 30 to about 55 wt % of a compound of formula I wherein n is 1 and each R 1 is independently selected and is a group R, b) from about 1 to about 20 wt % of a compound of formula I wherein n is 2 and each R 1 is independently selected and is a group R, c) from about 1 to about 10 wt % of a compound of formula I wherein n is 3 and each R 1 is independently selected and is a group R, and d) from about 25 to about 45 wt % of a compound of formula I which are pentaerythritol oligomers of 4 or more pentaerythritol monomer groups, wherein the wt % is based on the weight of all compounds of formula I present in the lubricant composition.