Water Aeration with Plunging Jets

摘要

Application of plunging water jets to large scale aeration processes is studied. Entrainment measurements made with various nozzle types with diameters up to 10 centimeters are given. A hydrodynamic model in which the plunging jet is continued below the water surface in a conical form is described. The entrained air in this biphasic cone is broken up into fine bubbles. This model contains four parameters which describe: (1) the water entrainment by the jet, (2) the gas fraction of the recirculating fluid, (3) the liquid velocity at which bubbles escape from the cone and (4) the ratio between the width of the downflowing liquid velocity and gas fraction profiles. The oxygen transfer from the air bubbles into the water of the plunging jet aerator is studied as well as the influence of contaminants on the aeration constant. Two examples of practical application of the plunging water jet: an aeration basin for the treatment of waste water and a fermentor for the production of yeast are presented. These examples confirm that plunging jet aerators can achieve mass transfer efficiencies up to 2 kgO2/kWh using air in commercial scale applications.