Abstract
This paper presents experimental research and mathematical modeling data concerning the impact of unit dynamic instabilities on the phase-transition condensation processes of the zeotropic mixtures R404A and R448A and azeotropic R507A refrigerants in pipe minichannels. The R507 refrigerant is currently used as a temporary substitute for R404A, whereas R448A is a sustainable prospective substitute for R404A. The study presents experimental testing data for the condensation processes of these refrigerants in pipe minichannels and a proposal for the use of dimensional analysis, including the Π-Buckingham theorem, to determine the regression relationship explaining the propagation of unit dynamic instabilities. Based on the experimental studies performed, regression computational models were developed and showed satisfactory agreement in the range of 20% to 25%. They give the possibility to identify, in a utilitarian, way the speed of propagation of temperature and pressure instabilities during the liquefaction of refrigerants. The study was carried out on pipe minichannels with an internal diameter of di = 3.3, 2.3, 1.92, 1.44 and 1.40 mm.
Highlights
R404A, R448A and R507A inIn the broadly understood field of application of energy machines and devices, various thermodynamic factors are used to carry out transitions and cycles
In the analysis of the literature discussed in this study, regarding the condensation phase transition of the R404A refrigerant in minichannels, attention was drawn to the lack of sufficient information on the use of its proposed substitutes, i.e., R507 and R448A
Type of refrigerant on the condensation mechanism under instability conditions, Impulsive wave propagation velocity of pressure instabilities moving in the two-phase condensation process, Impulsive temperature instability propagation velocity moving in the form of front condensation, Implementation of the assumptions concerning the solution of the aforementioned questions required appropriate experimental testing under the conditions in which they were realized for the R404A refrigerant
Summary
In the broadly understood field of application of energy machines and devices, various thermodynamic factors are used to carry out transitions and cycles. The dynamic instabilities observed in single- and multiple-phase media occurring during condensation in the minichannel flow may assume different forms This result stems from the nature of the disturbances that produce the instabilities, which depend on the following characteristics: Energies 2022, 15, 1789. In the analysis of the literature discussed in this study, regarding the condensation phase transition of the R404A refrigerant in minichannels, attention was drawn to the lack of sufficient information on the use of its proposed substitutes, i.e., R507 and R448A This deficiency is due to the wide application of these working agents in areas related to heat pumps, refrigeration and air-conditioning, which occur in stationary and mobile facilities
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