In this chapter, the flow patterns and pressure drops characterizing two-phase flows in U-bends are presented and discussed. These are illustrated by flow pattern visualizations and experimental pressure drops obtained with R134a flowing inside a test section with a 13.4mm internal diameter tube at two saturation temperatures (5 and 10°), three mass fluxes (150, 300, and 500 kgs−1 m−2) for three flow orientations (vertical downflow, horizontal flow, and vertical upflow). The experimental frictional pressure drop database obtained is presented and compared to the predictions of a newmulti-orientation flowpattern based U-bend frictional pressure drop model…