Two-phase flow visualization and pressure drop measurements of HFO-1234yf and R-134a refrigerants in horizontal return bends

Two-phase flow regimes of HFO-1234yf and R-134a in a horizontal 6.7 mm inner diameter return bend are investigated. The different flow regimes observed are: slug, intermittent and annular flows. The perturbation lengths up- and downstream of the singularity are experimental investigated and their contribution to the pressure drop is identified. It is shown that the upstream perturbation length is less than 10D and that the downstream perturbation length is less than 20D for the conditions tested in this study. In addition, this paper presents 574 pressure drop data points measured for two-phase flow of HFO-1234yf and R-134a in horizontal return bends of inner diameters (D) from 7.90 to 10.85 mm and curvature ratios (2R/D) from 3.68 to 4.05. The experimental pressure drop data in return bends is compared to four well-known prediction methods available in the literature. The whole present pressure drop in return bends experimental database for the next generation HFO-1234yf and for the R-134a refrigerants is presented in the appendix.

► Flow regimes of HFO-1234yf and R-134a in a horizontal return bend are investigated.
► Effect of pressure tap location up- and downstream of the return bend is studied.
► 588 original return bend pressure drop data points are measured.
► Database is compared to four well-known prediction methods from the literature.