VISUALIZATION AND TWO-PHASE PRESSURE GRADIENT IN RETURN BENDS: EXPERIMENTAL RESULTS FOR HFO-1234yf

Flow regimes of HFO-1234yf and R-134a in a horizontal and vertical 6.7 mm inner diameter glass return bend are investigated. The different flow regimes observed are: slug, intermittent and annular flows. In addition, this study presents 312 two-phase pressure drop data points measured for the HFO-1234yf refrigerant in horizontal return bends. Inner diameters (D) span from 7.90 to 10.85 mm and curvature ratios (2R/D) from 3.68 to 4.05. The present experimental data are compared against 4 correlations found in the literature. For the present database, none of these methods is able to satisfactorily predict the return bend pressure drop.