Two-phase pressure drop in return bends: Experimental results for R-410A

This study presents 238 pressure drop data points measured for two-phase flow of R-410A in horizontal return bends. The tube diameter (D) varies from 7.90 to 10.85 mm and the curvature ratio (2R/D) from 3.68 to 4.05. The mass velocity ranges from 179 to 1695 kg m−2 s−1 and the saturation temperatures from 4.6 °C to 20.7 °C. Preliminary tests show that the recovery length necessary for a correct pressure drop measurement downstream of the return bend is less than 20D, for the experimental conditions covered in this study. The singular pressure drop is determined by subtracting the regular pressure drop in straight tube from the total pressure drop. The experimental data are compared against four available correlations found in the literature. The present experimental database for the return bend pressure drop is presented in the Appendix A.