A Regressive Model for Periodic Dynamic Instabilities during Condensation of R1234yf and R1234ze Refrigerants

This paper presents the results of experimental research and mathematical modelling in terms influence periodic dynamic instabilities have on condensation phase change R1234yf R1234ze refrigerants tubular minichannels. The main reason for this was fact that under Montreal Protocol (1986), as well Regulation No 517/2014 European Parliament Council 16 April 2014, F-gases such hydrofluorocarbons (HFC), perfluorocarbons (PFC), sulphur hexafluoride, other agents containing fluorine to be withdrawn. includes one most commonly used refrigerants—R134a—which, since 1 January 2017, has already been It also R404A refrigerant. are suggested substitutions R134a. basic parameters determining application those their global warming potential (GWP) indicator, which is below 150, reduction fluorinated greenhouse gases emission by a third, simply withdrawing them (with 2010 reference level). current state knowledge enables researchers foresee some hydrodynamic Therefore, an expansion regarding substitutes absolutely necessary. Research concerning minichannels conducted currently being However, pro-ecologic not known. known during instabilities, propagation occurs waveform. Two-phase media particularly susceptible phenomenon. Propagation form acoustic wave or temperature, density mass, heat flux plays special role. All own characteristics, with evidently different velocities. Both mechanisms include irreversible dissipation dispersion. dissipative effects, irreversibility, cause entropy generation dump instability two-phase medium. dispersive effects function frequency. Besides results, contains dimensional analysis procedure based ?–Buckingham theorem allowed development regressive model velocities pressure instabilities. part using internal diameter dID = 1.40–3.3 mm.