Abstract
The following paper presents the results of preliminary experimental research on the influence of instabilities of a hydrodynamic type on the condensation phase change process in tubular minichannels. The research was focused on a new pro-ecological refrigerant, R1234yf, intended as a substitute for R134a that currently is being phased out. The flow condensation phase change process was investigated for both steady and un-steady conditions in singular tubular minichannels with an internal diameter d = {1,44; 2,30; 3,30} mm. The scope of the analysis of the experimental data covered an estimation of propagation velocities for both pressure and temperature instabilities as well as the shrinkage of the condensation zone. The results were also compared with the previous results obtained for the flow condensation phase change of R134a refrigerant in tubular minichannels with the same internal diameters.
Highlights
The refrigerant is a substance or a blend that circulates within a closed loop
An analysis of premilimary experimental research on hydrodynamic instabilities during condensation of the pro-ecological refrigerant R1234yf in tubular minichannels showed that: 1) For pressure instabilities, shape of the functions obtained for the R1234yf refrigerant (Figure 10) agree with the one for conventional channels (Figure 6)
Frozen velocity in minichannels is obtained for much smaller frequencies
Summary
The refrigerant is a substance or a blend that circulates within a closed loop. It absorbs heat while evaporating at a low temperature and pressure, and it rejects heat while condensing at a high temperature and pressure. The first agreement introduced the Ozone Depletion Potential (ODP) indicator that illustrates the negative impact of each refrigerant on the ozone layer. The second agreement introduced the Global Warming Potential (GWP) indicator that illustrates a contribution of each refrigerant to the global warming effect with carbon dioxide as a reference pollutant (GWPCO2=1). The EU Regulation No 517/2014, sets a roadmap for the phase-out of the so-known as fluorinated green-house gases – in particular hydro-fluoro-hydrocarbons (HFC), per-fluorohydrocarbons (PFC), sulphur hexafluoride and other fluorinated refrigerants. It aims at a 66% reduction in emission of fluorinated green-house gases (base level 2010).
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