In present study the pool boiling process for the model system of refrigerant 811(trichlorofluoromethane or CCl3F)/mineral compressor oil solution has been examined. The experiments performed at various boiling temperatures (40, 50, 60 degrees C) and initial mass fractions (3.485, 7.456, 14.000 mass.%) of compressor oil in the range of the heat fluxes 5-63 kW/m(2). The solutions were sampled 10 mm above, 10 mm below and at the level of the heater simultaneously with measurements of the heat transfer coefficient (HTC). We found that the oil concentration does not change with the level. However, the oil concentration considerably varies with the heat flux density and was always higher than the initial concentration value. The visual observations for the pool boiling process reveal that the concentration of solution depends on superposition between convective and diffusive components of the mass transfer. The data analysis indicates to significant underestimation of the HTC caused by change in the oil concentration. Finally, an influence of oil concentration change was examined for the refrigerant/oil solutions pool boiling with oleic acid surfactant and TiO2 nanoparticles additives. (C) 2019 Elsevier Ltd. All rights reserved.