POE Lubricant Candidates For Low GWP Refrigerants

Several series of polyol ester (POE) refrigeration lubricants have been investigated for low GWP refrigerant R32 (R-410A replacement) and HFO-1234ze (R-134a replacement). The main problem of R32/HFO refrigeration lubricant development can be summarized as balancing between miscibility, solubility and lubricity. Generally speaking, refrigerant-lubricant mixture with highly miscible property in low temperature evaporator will lead to more soluble phenomenon in high temperature compressor. Therefore, when refrigerant is well miscible with refrigeration lubricant, dissolved refrigerant will reduce working viscosity of refrigerant-oil mixture in compressor, and thus results in lower lubricity, wear of sliding parts, and compressor durability shortage. In our studies, the key factor which result in aforementioned phenomenon was found, and can be controlled independently by using optimized chemical structure. For R32 compressor system, we have successfully developed a series of POE refrigeration lubricant, with viscosities ranging from 32cSt to 90cSt at 40°C, and with a wide range of miscibility (20% oil) from -40℃ to 2℃. From results of PVT experiments and lubricity tests (Falex P/V and four ball), it demonstrated to be possible to develop a POE oil with high miscibility, low solubility and high working viscosity. All results in R32 system were better than traditional refrigeration lubricant in R410A system. Meanwhile, we also were able to identify the relationship between surface tension of chemical structure and lubricity. For HFO-1234ze compressor system, incumbent refrigeration lubricants suitable for R134a are almost fully miscible in HFO-1234ze, which could lead to severe refrigerant dilution of lubricant viscosity and poor lubricity due to high solubility. Through studies of chemical structure of refrigeration lubricants, reliable experimental tests and rigorous thermodynamic calculation, we created a range of POE lubricants (ISO68 to ISO220) with miscibility (20% oil) from -33℃ to -13℃, all the while, maintaining solubility and working viscosity on par with the common POE refrigeration lubricants currently used in R-134a system