Refrigeration Lubricants - Lubricants for Halogenated Refrigerants

CP-4600 SERIES synthetic hydrocarbon oils are similar to super-refined paraffinic oil. The fluid has a highly branched structure, which results in a low pour point. The length and position of side chains have been optimized to produce fluids with excellent viscosity/temperature characteristics. Absence of unsaturation and impurities contribute to excellent chemical stability in the presence of chlorofluorocarbon refrigerants. The high molecular weight and excellent thermal stability result in low volatility. These oils are produced in ISO viscosity grades ranging from 5 to 1000+.

CP-4600 SERIES fluids have been extensively used in rotary screw refrigeration compressor applications. The oils have good miscibility with R-12 and superior stability. Reports have also indicated superior adiabatic efficiency of three to ten percent in these compressors when compared to naphthenic refrigeration oils. This efficiency improvement is largely attributed to higher viscosity under dilution and temperature conditions. Selection of higher viscosity grades, not available with naphthenic oils, permits even higher efficiencies through an improved sealing effect. These same properties have contributed to the use of CP-4600 SERIES fluids in industrial heat pumps using R-114.

Lower evaporator temperatures are permissible than with mineral oils as CP-4600 SERIES fluids are wax free and have good low temperature fluidity for oil return. Low temperature fluidity is the major reason CP-4600 SERIES fluids have been used in the United States for relatively insoluble refrigerants such as Refrigerant-13 (R-13) and Refrigerant-503 (R-503). The lubricant viscosity, generally ISO 15 or 32 is selected by considering operating viscosity in the compressor as well as low temperature fluidity below -100°F (-73°C) in the direct expansion dry-type evaporator system. Generally, applications with Refrigerant-22 (R-22) are limited with CP-4600 SERIES fluids due to poor miscibility and require either higher evaporator temperatures, specially designed separation equipment, direct expansion evaporators, or oil reduced systems.

CP-1516 SERIES This type of synthetic has been used in R-12 heat pump applications in rotary screw compressors. The CP-1516 SERIES fluids were selected for their excellent viscosity temperature relationship and their lower tendency to absorb R-12. CP-1516 SERIES fluids are somewhat less stable than CP-4600 SERIES fluids but include additives for good stability in these systems. CP-1516 SERIES fluids have also been used with R-2. These oils have complete miscibility even at concentrations over fifty have complete miscibility even at concentrations over fifty percent by weight with R-22 to temperatures below -100°F (-73°C). CP-1516 SERIES fluids have excellent lubricity, low pour points, good low temperature fluidity, and good compatibility with most elastomers. Major drawbacks of these fluids are that they are somewhat hygroscopic, immiscible with mineral oils and require additives for good chemical and thermal stability. New developments with structural modifications show promise in overcoming these deficiencies.

CP-4214 SERIES fluids are made with higher molecular weight modified complex esters with high viscosity indexes and higher ISO viscosity grades. These oils have less effect on the swelling of elastomers than do the conventional neopentyl esters. The CP-4214 SERIES fluids represent a new class of refrigeration oils which have been carefully designed for high miscibility at lower temperatures with lower solubility at higher temperatures. All ISO viscosity grades were found to be completely miscible with R-22 to -90°F (-68°C) in concentrations tested from zero to forty percent by weight oil. High viscosity grades (ISO grades to 320) with high viscosity indexes have been developed to provide efficient compression sealing by compensating for the effect of the dissolved refrigerant while maintaining good oil return. In the case of rotary screw compressors where higher temperatures and pressures affect the oil in the reservoir or in systems without separation, the resultant viscosity of the oil/refrigerant must be adequate to provide hydrodynamic lubrication as well as to effectively seal the compressor. The CP-4214 SERIES fluids have been found to meet these requirements. The extreme miscibility of this lubricant with R-22 has made it an excellent candidate for low temperature applications. Since it is a synthetic, there is no possibility for wax precipitation (and no floc point). A high viscosity index and good low temperature fluidity adds to these properties for excellent low temperature behavior. Systems that include oil/gas separators will have the additional benefit of an extremely low vapor pressure. Improved volumetric efficiency and overall system improvements have led to the investigation of these products for potential compressor system efficiency improvements on a laboratory bench test basis and through field experience. Compressor bench tests have shown volumetric efficiency improvements up to ten percent. Field performance has shown miscibility with the refrigerant and better heats transfer properties of the lubricant itself. Recently, the CP-4214 SERIES fluids have been tested with R-502 and found to be miscible to very low temperatures when the ISO viscosity grade selected is ISO 150 or lower. Modified versions of the CP-4214 SERIES fluids are currently being investigated for possible applications with R-503 and R-13 for possible development of low temperature flooded evaporator systems.

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