Generation of a Monodisperse Microbubble Jet in Microgravity

Abstract

A new method to create a jet of a virtually monodisperse microbubble suspension of prescribed bubble size into a quiescent cavity is proposed. The method is insensitive to gravity and is based on the creation of a slug flow at a T junction in a capillary tube before injection. We develop a theoretical analysis that establishes the validity and efficiencyofthe method,ascontrolledbythecrossflowWebernumber,andyields asimple explicitprediction forthe bubble size in terms of the injection parameters. The method operates efficiently for small Weber numbers, yet it generates small bubbles of very uniform size. The reduced size dispersion is also explained within the theoretical model. The method of bubble formation, injection, and spreading by the resulting turbulent jet is validated experimentally in 4.7 s of free fall in the drop tower at the University of Bremen. Experiments demonstrate the physical principle behind the method of bubble formation and allow us to explore the dynamics of the resulting bubble jet after injection of the slug flow into a quiescent cavity in microgravity conditions as an efficient method of bubblespreadingandtransport.Detailed measurements of averagelocal velocities show thatbubblesare essentially passivewithrespecttothecarriermean flow,andtheinherentturbulenceofthe flowiscrucialforoptimalspreading of the bubbledistribution andreduction of bubble coalescence. Theshape of the bubblejet isstudied asa function of the Reynolds number. Finally, the degree of coalescence is also characterized and found to be remarkably small.