TITLE: Etude de l'entrainement de gouttelettes a la surface libre du liquide dans une colonne a bulles. (Study of droplet entrainment from bubbling surface in a bubble column)

AUTHOR: M. Ramirez de Santiago.

INST.  AUTHOR: CEA Centre d'Etudes Nucleaires de Grenoble (France);  Grenoble-1 Univ., 38 (France).

LANGUAGE: French

PUB.  TYPE: Thesis

PUB.  COUNTRY: France

SOURCE: Department of Energy [DEE],  May 91,  358p.

NTIS ORDER NO.: DE92743657INW

ABSTRACT:

In a bubble column droplets are ejected from the free surface by bubble bursting or splashing. Depending on their size, the droplets are partly carried away by the streaming gas or fall back to the bubbling surface by gravity force. Experiments have been carried out to determine the void fraction in the column by means of an optical probe. In the interfacial zone the bubble bursting process was captured with a high-speed video camera. Simultaneous measurements were made of size and velocity of droplets at several distances from the bubbling surface with a Phase-Doppler Anemometry. The bubble column can be divided into three regions: A lower zone with a flat profile of the local void fraction, a central zone where the flow regime is steady and an upper zone where the local void fraction grows rapidly. A two-parameter log-normal distribution  function was proposed in order to describe the polydisperse distribution of droplet-size. Results were obtained concerning the entrainment, concentration, volume fraction and interfacial area of droplets. Finally, it was found that the turbulence intensity affects the droplet terminal velocity for droplets smaller than the Kolmogorov microscale. (ERA citation 17:004406)

REPORT  NUMBER: FRCEA-TH-351