EXPERIMENTAL INVESTIGATIONS ON THE CONDENSATION OF STEAM BUBBLES INJECTED INTO SUBCOOLED WATER AT 1 MPA

Abstract

Bubble condensation plays an important role, e.g., in subcooled 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 modeling of the condensation process. To develop and validate closure models for computational fluid dynamics codes, new experimental data are required. The effect of bubble sizes is clearly shown in experimental investigations done at the TOPFLOW facility of Forschungszentrum Dresden Rossendorf. Steam bubbles are injected into a subcooled upward pipe flow via orifices in the pipe wall located at different distances from the measuring plane. Injection orifices measuring 1 and 4 mm are used to vary the initial bubble size distribution. Variation of the distance between the location of the gas injection and the measuring plane allows investigation of the evolution of the flow along the pipe. Measurements are done using wire-mesh sensors and thermocouples. Condensation is clearly faster in the 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.