MN-00-09-3 -- Effects of Lubricant Miscibility and Viscosity on the Performance of an R-134a Refrigerating System PDF

The effects of lubricant miscibility and viscosity were evaluated by measuring the performance of a hydrofluorocarbon R-134a refrigerating system operating with three different lubricants. First, the effects of refrigerant/lubricant miscibility were investigated by comparing the performance of a miscible polyolester lubricant (POE) and an immiscible naphthenic mineral oil (MO) of similar viscosity grade. The coefficient of performance (COP) of the operating R-134a refrigerating system was found to be consistently higher, up to 5%, for the miscible POE lubricant compared to the immiscible mineral oil when the results were compared at the same test conditions. The increased performance for the POE operation is attributed to both a lower compressor power consumption and a higher evaporator capacity. Second, lubricant viscosity effects were investigated by comparing the R-134a system performance of two miscible POE lubricants of different viscosity grades, namely, an ISO 22 and an ISO 32. The results show that both the COP and capacity are generally higher, up to 3.5%, for the system employing the lower viscosity POE. In summary, R-134a refrigerating system performances can be improved by usage of both miscible lubricants and by usage of lubricants with lower viscosities.

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