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

摘要

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 10. D and that the downstream perturbation length is less than 20. D 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 (2. R/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.