Vol 104, No 12 (2015)

The results of the experimental research of the heat exchange at bubble boiling of R404А, R407С and R410А refrigerants on finned tubes are cited. The experiments were carried out at 13...28,5 оС saturation temperatures. It was established by experiments as well as theoretically that at the developed bubble boiling the intensity of the heat transfer didn’t depend on the type or profile of the nonisothermic finned surface but it was defined only by operation parameters, thermophysical properties of the liquid, geometrical dimensions of the finned surface as well as by the internal characteristics of the boiling process. The heat transfer coefficients at the refrigerant boiling on a finned surface was rather higher than on the smooth one, i.e. at developed bubble boiling the heat exchange on finned surfaces was 2-4 times higher than on the smooth ones. The empiric dependences were defined that allowed finding the heat transfer coefficient at R404А, R407С and R410А refrigerants boiling on the finned surface of a big volume; they were satisfactorily agreed with the experimental data, the error was 15-20%. The possibility of using the derived dependences to calculate heat exchange apparatuses of the evaporating type with finned surfaces was shown. Keywords: heat exchange at boiling, vaporization, mixed ozone safe refrigerant, heat exchange intensity, heat transfer coefficient, finned surfaces, evaporator, heat exchange apparatus, refrigerating plant, empiric dependence.

The freezing spherical watersaturated granules using the negative temperature air blowoff of their surface was examined. A generalized equation for calculation of the frozen layer thickness of the spherical watersaturated granule depending on the duration of the process was derived. The experimental bench and the method of the research carrying out were described. The experimental data were compared with the calculated indices obtained on the basis of the generalized process equation. A construction arrangement of a cold accumulating watercooling tower that uses the negative temperatures potential of the ambient air to accumulate water ice was offered. The results of the research may be used when designing the cold accumulating watercooling towers. Keywords: spherical granules, water ice accumulation, electric power saving, lowpotential energy source, cold accumulating watercooling tower, negative temperatures, ice water, phase transition.