Two-phase flow of HFO-1234yf, R-134a and R-410A in sudden contractions: Visualization, pressure drop measurements and new prediction method

This study presents qualitative two-phase flow visualizations of R-134a in a 10 mm glass tube with a cross-section area ratio (σAσA) of 0.49. Flow patterns across the sudden contraction are simultaneous observed by top and side views with a high speed high resolution camera. The perturbation lengths up- and down-stream of the sudden contraction are experimentally investigated and their contribution to the pressure drop is identified. In addition, 360 pressure drop data points measured for two-phase flow of HFO-1234yf, R-134a and R-410A refrigerants in horizontal sudden contractions are presented and included in the appendix. The experimental pressure drop data are compared against six prediction methods from the literature. The best prediction is given by the method of Abdell et al. [1] with 54% of the data predicted within a ±30% error band. Based on the present database, a new method is proposed for predicting the pressure drop in sudden contractions, which is the sum of the pressure drop due to the flow acceleration in a geometrical area change (change in momentum) and the frictional pressure drop due to the singularity and its perturbation effects up- and down-stream (proposed equation). This new method predicts almost 95% of the database within a ±30% error band.

► Two-phase flow visualizations of R-134a in a 10 mm glass tube.
► Perturbation lengths up- and downstream of the sudden contraction are investigated.
► 360 Pressure drop data points of three refrigerants in horizontal sudden contractions are presented.
► A new method is proposed for predicting the pressure drop in sudden contractions.