1. Objectives and motivations Experimental setup Results Conclusions
VISUALIZATION AND TWO-PHASE PRESSURE GRADIENT IN RETURN BENDS: EXPERIMENTAL RESULTS FOR HFO-1234yf
PADILLA M.(*), REVELLIN R.(*), HABERSCHILL P.(*), BONJOUR J.(*)
(*) Université de Lyon, CNRS. INSA-Lyon, CETHIL UMR5008, F-69621, Villeurbanne, France,
Université Lyon 1, F-69622, France
Objectives and motivations
Experimental setup
Growing interest in refrigerant charge reduction
A change in the design of the evaporator and condenser coils is required: they must become more compact ( the effect of the singularities becomes more important).
Significant lack of data points for pressure drop in singularities
Two parallel loops: the refrigerant loop and the water-glycol loop.
Test section for visualizing both horizontal and vertical down flow two-phase flow regimes in return bend.
Test section for pressure drop measurements in return bends.
Flow visualization
Charnay et al., (2011)
23rd IIR International Congress of Refrigeration
Perturbation lengths
Refrigerant circuit
Pressure drop measurements
Visualize flow regimes of HFO-1234yf and R-134a in horizontal and vertical return bends.
Present HFO-1234yf new two-phase frictional pressure drop data points for two-phase flow in horizontal return bends
Results
Two-phase flow regimes visualizations in return bends
Horizontal
(a) HFO-1234yf,
G = 300 kg∙m-2∙s-1, x=0.05, Slug flow
(b) HFO-1234yf,
G = 300 kg∙m-2∙s-1, x=0.20, Intermittent flow
(c) HFO-1234yf,
G = 300 kg∙m-2∙s-1, x=0.60, Annular flow
(d) R-134a,
G = 300 kg∙m-2∙s-1, x=0.05, Slug flow
(e) R-134a,
G = 300 kg∙m-2∙s-1, x=0.20, Intermittent flow
(f) R-134a,
G = 300 kg∙m-2∙s-1, x=0.60, Annular flow
Vertical
(g) HFO-1234yf,
G = 300 kg∙m-2∙s-1, x=0.05, Slug flow
(h) HFO-1234yf,
G = 300 kg∙m-2∙s-1, x=0.20, Intermittent flow
(i) HFO-1234yf,
G = 300 kg∙m-2∙s-1, x=0.60, Annular flow
(j) R-134a,
G = 500 kg∙m-2∙s-1, x=0.05, Slug flow
(j) R-134a,
G = 500 kg∙m-2∙s-1, x=0.20, Intermittent flow
(l) R-134a,
G = 500 kg∙m-2∙s-1, x=0.60, Annular flow
Return bend pressure drop
Comparison to prediction methods
Flow bend inlet
Wojtan et al. (2005)
flow pattern map o) m) q) r)
Perturbation length p) n) s) t)
Conclusions
Flow regimes observed for HFO-1234yf and R-134a were: slug, intermittent and annular flows.
The Wojtan et al. (2005) flow pattern map was able to satisfactorily predict the HFO-1234yf flow regimes at the inlet of the return bend.
Observations in the curved section of the return bend show that the distribution of the phases is influenced by a combination of the gravity and the effect of the centrifugal force.
There was no significant difference in the return bend pressure drop above 20D (downstream) and 10D (upstream).
588 pressure drop data points measured in horizontal return bends have been presented for the next generation refrigerant HFO-1234yf and the R-134a.