A New High-Pressure Viscometer for Oil/Refrigerant Solutions and Preliminary Results

Abstract

The reliability and efficiency of refrigeration compressors is dependent on the lubricating effectiveness of the refrigeration oil which is necessarily a solution of oil and refrigerant. In this article, the development of a high pressure viscometer, which can operate at elastohydrodynamic lubrication (EHL) inlet pressures for oil/refrigerant solutions, is explained in detail. New viscosity measurements are presented for two compressor oils to 1.2 GPa. Preliminary results are given for a polyol ester with two concentrations of R134a refrigerant to 0.35 GPa. These are the first measurements of oil/refrigerant solutions to such high pressure. Temperature-pressureviscosity correlations are applied to all materials for use in modeling. Correlations are provided for the temperature and pressure dependences of the viscosity of the oils, the refrigerant and for the mixtures. The definition of -pressure-viscosity coefficient‖ is a pressing problem for elastohydrodynamics.

The high‐pressure viscosity of refrigerant/oil systems

“…The viscometer employed for all measurements is the pressurised falling sinker type. It is described in detail with pictures of the disassembled components in the work of Bair . The present viscometer only differs from the description in the work of Bair by the sinkers.…”

“…It is described in detail with pictures of the disassembled components in the work of Bair . The present viscometer only differs from the description in the work of Bair by the sinkers. A new solid tantalum‐core sinker with average density of 13300 kg m −3 was used for all measurements on refrigerant containing liquids.…”

Progress in rolling bearing technology for refrigerant compressors

“…Many studies have been carried out in the past to measure or to estimate the film thickness in EHL contacts lubricated with oil-refrigerant mixtures. [3][4][5][7][8][9][10][11][12] More recent studies of oil-refrigerant mixtures in EHL are in Bair et al 24,25 and Tuomas. 26 In the calculation of film thickness in EHL contacts lubricated with oil-refrigerant mixtures the estimation of the mixture properties is a key intermediate step.…”

“…with M being the molecular weight of the component. In an example 24 with polyol ester oil (POE) and HFC-134a, a value of m ¼ 4:5 is reported. In Bair, 24 a different mixture law is used for the viscosity; however, it also depends on the ratio m: The molecular weight of oil varies with oil viscosity and oil type.…”

“…The molecular weight of refrigerants is typically 100 to 150 g/mol. As explained in Bair, 24 the molecular weight of the oil can be calculated backwards with equation 2, if measurements of viscosity of the mixture at different dilution rates are known. Equations (1) and (2) can be plotted for different refrigerant dilution rates and molecular weight rations, as shown in Figure 4.…”