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

Abstract

Two-phase flow regimes of HFO-1234yf and R-134a in a horizontal 6.7mm 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 10.85mm 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.