A rotatable bell is provided having a generally downwardly diverging shape about a central vertical axis, with the outer wall surface of the bell including a circumferentially extending jet flow surface portion with a plurality of gas flow wall openings circumferentially disposed around the base part...http://www.google.es/patents/US4066722?utm_source=gb-gplus-sharePatente US4066722 - Apparatus for sparging gas into liquid
