Time extender photography for determining the size of bubbles and for analyzing oscillations of the phase boundary while forming superheated steam bubbles at cylindrical single nozzles

Time extender photography proves to be suited for the detection of phase boundaries in heterogeneous two-phase flows. A possibility of application is shown for the feed-in of superheated steam into water of saturation temperature at high system pressures and temperatures by means of experimental studies on bubble formation and separation with simultaneous heat transfer. The present paper is intentionally confined to the results gained from time extender photography. The relations between bubble size as well as frequency of formation and the physical parameters of the system, important for the specification of transport quantities, are given for the experimentally considered range and the cause for the sudden change from steady gas flow (formation of single bubbles) into unsteady gas flow (combination of bubbles during separation from the nozzle) is revealed as a build-up problem and covered by proper formulae. (orig./ORU)