The phase distribution, the bubble velocities and the thermal expansion behaviour of the bubbles in two-phase bubbly slit flow were examined by using high-speed cinematography. The phase distribution in (adiabatic) hashing water and non flashing air/water flow is relatively homogeneous. Under all flow conditions the slip ratio in the one dimensional flow is less than 1.2. It can be recalculated by assuming the pressure and the friction forces on the bubble surface in equilibrium. The cavitation in a slightly subcooled liquid occurring at a sharp edged slit inlet has a significant influence on the post-evaporation behaviour. In principle, the assumption of a homogeneous mixture flow in thermodynamic equilibrium is validated, the deviations are mutually neutralizing to a large extent.