An experimental investigation and modelling of the thermodynamic properties of isobutane–compressor oil solutions: Some aspects of experimental methodology

This paper presents experimental data for the solubility, density and capillary constant for solutions of natural refrigerant isobutane with commercial mineral compressor oil Azmol over a wide range of temperatures and concentrations. Based on information for the capillary constant, the surface tension of the solutions isobutane/Azmol is determined. The experimental data were obtained in the temperature range from 303 K to 363 K and at pressures up to 1.7 MPa using static methods. The experimental data obtained for the solutions of the natural refrigerant isobutane with the commercial mineral compressor oil Azmol are sufficiently described with the help of correlations based on the theory of thermodynamic similarity. The paper reports variation of the vapor pressure, density, capillary constant and surface tension as a function of concentration for the isobutane/Azmol solutions. The enthalpy of liquid phase of the isobutane/Azmol solutions is calculated. The analysis of the behaviour of the excess thermodynamic functions is carried out. The paper examines experimental and methodical uncertainties in the investigation of thermodynamic properties of the refrigerant/oil solutions (ROS). The influence of the time taken to establish thermodynamic equilibrium in the experimental cell on the uncertainty of the experimental data for gas-saturated mixtures such as ROS is discussed. Information about the changing concentration of refrigerant in the liquid phase of the ROS and in the surface layer of the liquid phase of the ROS at increasing temperature is presented. In addition, the experimental data for the density, surface tension and refractive index of the mineral compressor oil Azmol are reported.