Viscosity, Density, and Gas Solubility of Refrigerant Blends and Azeotropes in Selected Refrigerant Lubricants

Data is presented for the vapor liquid equilibrium viscosity reduction of lubricants with two refrigerant blends at two temperatures. The lubricants tested were a 32 ISO VG mixed acid polyolester and a 32 ISO VG branched acid polyolester. The refrigerant blends used were HFC-125/143a/134a (44/52/4% w/w), and HFC-125/143a (50/50% w/w). INTRODUCTION This experiment detennined the vapor liquid equilibrium viscosity reduction of two lubricants with two refrigerant blends. The lubricants tested were a 32 ISO VG mixed acid polyolester and a 32 ISO VG branched acid polyolester The refrigerant blends used were HFC-125/143a/134a (44/52/4% w/w), and HFC-125/143a (50/50% w/w). The mixtures were prepared and tested in an oscillating body viscometer, and the ratio of gases at each viscosity data point was determined by gas chromatography. METHODS The viscosity determination method used in this study is similar to the gas equilibrium approach described by Parmlee (1964), Albright (1956-59) and Little (1956). This study uses temperature and pressure limitations to detennine refrigerant gas concentrations. Viscosity and density are determined accurately by a fourth generation viscometer (Cavestri, 1993) taken from a report by Nissen (1981). This instrument consists of a solid cylindrical bob made of highly polished stainless steel, which is enclosed in a stainless steel pressure tube. The bob is connected to a precisely thermostatted spring inside the tube. An external electromagnet causes the bob to oscillate inside the solution-filled tube. The rate at which the bob's motion slows and stops is called the decrement. The viscosity of the solution can be determined from the decrement and density. The same bob used to measure the decrement can be used for density measurements. Observations of changes in the position of the bob can determine density to within .0005 g/ml. Accurate density measurements allow the calculation of centistokes (eSt) from centipoise (cP). The readability of the viscometer is 0.06 cP. The wide temperature range of various calibration oils results in a significant overlap that serves as an internal standard and self check. For low viscosity solutions, the difference between standards is ±0.1 %; this increases to ±1.5% for high viscosity solutions. The density range of the instrument is calibrated with known, readily available pure fluids that are dried over a molecular sieve prior to use; this provides a straight calibration line for density at specified temperatures. The precision of this determination is ±0.3%