Performances Investigation For The New Azeotropic Refrigerants Used In Cascade Refrigeration Temperature Range

There are many wide applications in the temperature range of -80℃, such as biology, iatrology, biophysics, life science, and so on. Generally, the lowest effective refrigeration temperature for a traditional vapor-compression cycle is about -40℃, limited by the pressure ratio, condensing temperature and evaporating temperature. In order to achieve a lower temperature of -80℃, a two-stage cascade refrigeration cycle is necessary.In the low temperature stage of a two-stage cascade system, R13, R23 and R503 are the traditionally used refrigerants. However, because of their high ozone depletion potential (ODP) values and global warming potential (GWP), the usage of those kinds of refrigerant are limited and finally forbidden. So the popularly used refrigerant in the low temperature stage is R508B now, which is an azeotropic mixture of R23 and R116, still with a large GWP value because of its HFC and FC components. Furthermore, the refrigerant of R508 is less soluble in compressor lubricant, which would lead to a reduction of system reliability. So, it is necessary and important to find some effective and environment-friendly alternative refrigerants used in the low temperature stage of the two-stage cascade refrigeration cycle. It is self-evident that the investigation on refrigerating performances is essential for alternative refrigerants. Capacity measurements for the new azeoreopic refrigerants have been conducted by the author, which are presented as follow:1.Refrigeration performance calculation for new mixturesWith a software of REFPROP7.1, the thermodynamic performances of some new proposed refrigerant mixtures and R508B were compared by calculation of such important parameters as COP, pressure ratio, discharge temperature and volumetric refrigerating capacity. It is clear that, the new azeotropic mixtures of R170+R116 and R170+R116+R23 have better performances.2.Design and establishment of an experimental apparatus for performance testOn the basis of patents of CN2364403Y, CN2694182Y, CN1485589A and GB/T5773-2004, an experimental apparatus was designed and fabricated. High precision thermometers, pressure transmitters were used to obtain the precise data. Furthermore, the experiment apparatus is designed to adapt to different kinds of refrigerants for cascade refrigeration systems.3.Research on traditional refrigerants for cascade refrigeration systemsThermodynamic performances of COP, pressure ratio and refrigerating capacity for five traditional refrigerants of R13, R23, R503, R508A and R508B were messured at different condensing temperatures and evaporating temperatures. Based on the environmental features and thermodynamic performances, disadvantages of these traditionally used refrigerants in the low temperature stage of a two-stage cascade refrigeration cycle were analyzed. The results obtained in this study are useful for searching some effective and environment-friendly alternative refrigerants and further experimental capacity comparison.4. Research on new refrigerants for cascade refrigeration systemsSeries binary and ternary azeotropic mixtures of R170, R116 and R23 have zero ODP and less GWP values were proposed and their performances were measured and compared with R508B. All of them show good potential for use in cascade refrigeration system for -80℃applications.