Vol 106, No 11 (2017)

HFC refrigerant mixtures are widely used now in cold supply and air conditioning systems. R404А, R410A, R407С are the most popular of them. But the list of HFC refrigerant mixtures is not limited by these refrigerants. The paper envisages the properties, fields of application, environmental characteristics of HFC refrigerant mixtures that are not well known. The statutes of EU regulations ЕС 517/2014 on phasing out of fluorinecontaining gases by 2030 are cited. A diagram presentation of the values of refrigerant mixtures GWP in comparison with R134a is given. It is recommended to replace refrigerant mixtures at high GWP with R134a during an interim period until HFO refrigerants are tested, studied on safety and price reducing.

The paper presents the results of the experimental study of the stage of a radial axial centripetal turbine at 1,3 kW capacity to drive a highfrequency electric generator at 1 kW nominal capacity that is a part of the plant operating on the organic Rankine cycle. In cryogenic engineering a considerable volume of data on design of centrifugal radial axial lowtemperature turboexpanders at capacity from 100 W to 1MW at 10,000-500,000 rpm with 15-500 mm runner outer diameter and expansion ratio up to 30 in one stage has been accumulated. This experience was used when developing a compact highspeed turbomachine. The major geometric proportions of the turbine setting were defined on the base of the experience of the cryogenic turboexpander design. The paper cites the results of calculations and experimental study of supersonic flow in the distributor and the turbine runner stage. Analytical calculations of the turbine stage efficiency and the results of detailed numerical modeling agree well with the experiment data confirming by that the miniturbine COP at a level near to 75%.