Behavior of liquid droplet in stream of gas

Question

Hail to all magnificent physicists from a humble chemist! :)

I'm working on an experimental setup for investigation of homogeneous nucleation and crystal growth in container-free environment. Well, actually, just trying to think about all potential pitfalls and problems before designing any actual apparatus.

I've thought and get to know about many terrestrial options for "levitating" a droplet of liquid, and settled for aerodynamic levitation, as any other option requires high voltage, enormous magnetic fields or lasers to work with non-conducting, room temperature samples. My budget and I prefer cheap and mendable options.

So, idea is to setup variable speed/variable temperature stream of gas (i.e. nitrogen) which is saturated with liquid vapour to prevent evaporation of droplet. Gas would be flowing in upward direction and in laminar fashion. Furthermore, liquid is a pure substance with known and well defined physical properties (density, surface tension, possibly anything that could be used to model this problem).

My questions are:

Is there any known oh-yes-this-works-for-this model or simulation tool with which I could predict what would happen with liquid droplet in that gas stream? (by so, ignoring evaporation and any boundary conditions except for one between gas and liquid droplet) If not, could you suggest where to start?

Is there any way to predict maximum spherical droplet size which would remain stabile (which would not disintegrate into smaller droplets). If not, are there any special shapes which would be stabile in this environment?

Thank you,

Edi

Answer 1

This report seems to contain most, if not all, of the physics you need: Holterman's Kinetics and evaporation of water drops in air (eprint, mirror, mirror2).

But considering raindrops will probably already give you good estimates:

• it doesn't seem you can't get drops bigger than 9 mm across;
• but the bigger the droplet, the more squeezed it is;
• for them to be really stable, you'll probably have to keep them below 5 mm;
• that will require an airflow with speeds of less than 10 m/s.

You have an early, 3-page paper by Spilhaus: Raindrop size, shape and falling speed (eprint). Its values are essentially confirmed by other sources.

If you do want to simulate this system, though, you'll need a good piece of software. I've heard of OpenFOAM, COMSOL Multiphysics, Fluent, SPH-flow, and others, but I can't really advise on this subject.

As an aside: this concept has been used in an artwork by Alistair McClymont. It seems to be easy enough to achieve, but if you want to avoid the strong airflow, you might consider a different option using sound waves: Acoustophoretic contactless transport and handling of matter in air (eprint).