Abstract
This paper presents the results of experimental research and mathematical modelling in terms of the influence periodic dynamic instabilities have on condensation phase change in R1234yf and R1234ze refrigerants in tubular minichannels. The main reason for this research was the fact that under the Montreal Protocol (1986), as well as Regulation No 517/2014 of the European Parliament and of the Council of 16 April 2014, the F-gases such as hydrofluorocarbons (HFC), perfluorocarbons (PFC), sulphur hexafluoride, and other agents containing fluorine have to be withdrawn. This includes one of the most commonly used refrigerants—R134a—which, since 1 January 2017, has already been withdrawn. It also includes the R404A refrigerant. R1234ze and R1234yf are suggested as substitutions for R134a. The basic parameters determining the application of those agents are their global warming potential (GWP) indicator, which is below 150, and reduction in fluorinated greenhouse gases emission by a third, simply by withdrawing them (with 2010 as a reference level). The current state of knowledge enables researchers to foresee the influence of some hydrodynamic instabilities on the condensation of fluorinated refrigerants in minichannels. Therefore, an expansion of this knowledge regarding the suggested substitutes is absolutely necessary. Research concerning the condensation in minichannels under dynamic instabilities was already conducted for the refrigerants currently being withdrawn. However, the influence of those instabilities on a phase change in the suggested pro-ecologic substitutes is not known. It is known that during the condensation of refrigerants under dynamic instabilities, the propagation of instabilities occurs in a waveform. Two-phase media are particularly susceptible to this phenomenon. Propagation of instabilities in the form of acoustic wave or wave change in other parameters such as temperature, the density of mass, or heat flux plays a special role. All of them have their own characteristics, with evidently different propagation velocities. Both mechanisms include irreversible dissipation and dispersion. The dissipative effects, by their irreversibility, cause entropy generation and dump the instability propagation in a two-phase medium. The dispersive effects influence the instability propagation that is a function of the generation frequency. Besides the experimental results, the paper contains a dimensional analysis procedure based on the Π–Buckingham theorem that has allowed for the development of a regressive model for the velocities of pressure dynamic instabilities. The experimental part of this paper was conducted using tubular minichannels with an internal diameter of dID = 1.40–3.3 mm.
Highlights
It is necessary to investigate the influence of hydrodynamic instabilities on phase change in suggested substitutes of withdrawn gases, especially condensation in pipe minichannels [4]
It was found that condensation heat transfer coefficients of R1234ze(E) and R134a decreased with an increase in reduced pressure
The process was studied in relation to condensation heat transfer performance, and integrated correlations of low global warming potential (GWP) refrigerants in plate heat exchangers were investigated [6]
Summary
After 50 years, the era of the application of chlorinated refrigerants (freons) is coming to an end. This paper presents the issues concerning phase changes in condensation inside minichannels, which were investigated for R134a refrigerants, as well as for their substitutes R1234ze and R1234yf, respectively This is because the refrigerants are used as a working fluid for a wide spectrum of applications—namely, heat pumping, refrigeration, and air conditioning (both stationary and mobile) [11,12]. This is because the refrigerants are used as a working fluid for a wide spectrum of applications—namely, heat pump3ionfg refrigeration, and air conditioning (both stationary and mobile) [11,12].
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.