Particle fountains in a confined environment*

We present an experimental investigation of particle-laden fountains in a confined environment. These experiments are complimented by simplified theoretical models which provide insight into the underlying physics. 

The multiphase fountains are produced by issuing a mixture of fresh water and Silicon-Carbide particles upwards through a nozzle into a laterally confined water tank. The mixture issues through the nozzle as a dense particle-laden jet that decelerates owing to its negative buoyancy and the entrainment of ambient liquid. The fluid rises to a finite height before falling back to the floor.

We investigate the motion of the particles in the fountain and in the confined environment. We find that the fate of the particles depends on the terminal particle fall speed compared to (i) the characteristic velocity of the fountain in the jet-like core, (ii) the maximum upward velocity in the ambient fluid outside the fountain and (iii) the upward velocity in the ambient fluid above the top of the fountain. From this comparison we identify four regimes that provide a framework for interpreting the fate of particles carried by liquid jets in a confined space.