AbstractAn experimental and analytical study of adiabatic countercurrent flow limitation (flooding) in single vertical ducts is reported. The experiments were carried out in a rectangular channel using saturated liquid and vapour of Refrigerant 12 (CCl2F2). The steady‐state liquid delivery (flooding) curves as well as local pressure drop and void fraction distributions in the countercurrent flow were measured in a range of system pressures fromp/pcrit= 0.16 top/pcrit= 0.31, and for various total liquid injection rates and locations. The measured flooding curvesj1=f(jg) as well as pressure drop and void fraction during partial liquid delivery (j1