Simultaneous Measurement of Solubility, Density, and Viscosity of Lubricants with CO{sub}2 (R-744) at High Temperature and Pressures for Refrigerating System

摘要

Solubility of carbon dioxide (R-744), liquid density, and dynamic viscosity were simultaneously measured for R-744 + lubricant by using a recirculating type apparatus equipped with a densimeter and a viscometer at the temperature of 377.6 K and the pressure up to 20.11 MPa. The lubricants employed were two synthetic oils, where the main component is poly (alkylene glycol) (PAG) or polyolester (POE). Decane (C{sub}10H{sub}22) and Tetraethylene glycol (TEG) were also employed as model substances. Prior to the measurement, the solubility of R-744 and the liquid density were measured for R-744 + C{sub}10H{sub}22 at 377.6 K, and ensured the reliability. In the three systems, R-744 + TEG, R-744 + PAG, and R-744 + POE, the two coexisting phases were observed in the whole range of the pressure. The solubility of R-744 was increased with pressure for PAG, and POE. The other hand, the solubility in TEG was almost stayed constant at the higher pressure than 18 MPa. The liquid density was decreased with the pressure. However, the tendency was broadly divided into the two types. The pressure dependence for the R-744 + POE showed a convex shape, and that for the R-744 + TEG and the R-744 + PAG showed a concaved shape. The phase behaviour of the R-744 + PAG and the R-744 + POE was similar to vapor-liquid equilibrium. That of the R-744 + TEG was similar to liquid-liquid equilibrium. The logarithmic dynamic viscosity was linearly decreased with the weight fraction of dissolved R-744. The dependence for the R-744 + TEG was smaller than that for the R-744 + PAG. Considering the results, TEG is expected to be a new type lubricant for an alternative refrigerant, R-744.