Experimental investigations on the condensation of steam bubbles injected into sub-cooled water

Bubble condensation plays an important role e.g. in sub-cooled boiling or steam injection into pools. Since the condensation rate is proportional to the interfacial area density, bubble size distributions have to be considered in an adequate modelling of the condensation process. To develop and validate closure models for CFD codes new experimental data are required. The effect of bubble sizes is clearly shown in experimental investigations done at the TOPFLOW facility of FZD. Steam bubbles are injected into a sub-cooled upward pipe flow via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices are used to vary the initial bubble size distribution. The variation of the distance between the location of the gas injection and the measuring plane allows investigating the evolution of the flow along the pipe. Measurements are done using wire-mesh sensors and thermocouples. Condensation is clearly faster in case of the injection via the smaller orifices, i.e. in case of smaller bubble sizes. Data on averaged void fraction, radial gas volume fraction profiles, profiles of the gas velocity and bubble size distributions in dependency of the L/D ratio are presented in the paper.