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

ARTI MCLR DOE/CE/23810-46 (Abstract)

by Richard C. Cavestri, Ph.D.

The lubricants tested in this project were chosen based on the results of liquid/liquid miscibility tests.  EMKARATE RL32S and Emery 2968A were selected.  The Vapor Liquid Equilibrium (VLE) viscosity reduction and gas fractionation of each was measured with three different refrigerant blends: 1) R-404A; 2) R-507; and 3) R-407C.  In addition, the four single refrigerants that make up the blends, HFC-32, HFC-125, HFC-134a, and HFC-143a, were also measured.

Lubricants found to have the lowest liquid/liquid miscibilities had nearly equal viscosity reduction profiles, as did the more miscible lubricants.  Analytical methodology consisted of maintaining equally both the composition of the head space vapor above the lubricant/refrigerant mixture, and the composition of the liquid blend refrigerant.  Blends with large temperature glides were re-evaluated in order to test the concept of head space quality and a vented piston hydraulic cylinder assembly was developed to perform this task.  Fluid property data, above critical temperature and pressure conditions, is presented for the two lubricants with HFC-32, HFC-125, HFC-143a refrigerants.

This research shows that the lubricant EMKARATE RL32S, which had the lowest (poorest) liquid/liquid miscibilities with the selected refrigerants, also had nearly equal viscosity reduction profiles to the more miscible Emery 2968A lubricant.  The analytical methodology consisted of maintaining the composition of the refrigerant gas above the lubricant to be equal in composition to that of the pure liquid refrigerant blend being introduced into the lubricant.  Refrigerant blends with large temperature glides were re-evaluated in order to validate the concept of the importance of the composition of the gas over the lubricant.  To do perform this task, a special vented piston hydraulic cylinder assembly was developed.  Fluid property data is also presented for HFC-32, HFC-125, and HFC-143a above the critical temperature and pressure of each.

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