Generation and Control of Particle size distributions for Optical Velocity Measurement Techniques in Fluid Mechanics

Kurzfassung

It is shown in the paper that high concentrations of narrow band particle size distributions with a mean diameter below one micrometer can be easily generated by means of multi hole nozzles under over-critical pressure conditions (>1 bar) provided the kinetic energy, entering the liquid volume, is above a certain value. This experimental result can be explained by assuming that the nozzle has basically three functions. Firstly, it generates the particles at the nozzle exit. Secondly, it changes the fluid mechanical state of the fluid into a two phase liquid which seems to promote the generation of smaller particle size distributions as the fluid mechanical parameters are different. Thirdly, the remaining kinetic energy which is not consumed for the generation of the particles or the transition of the fluid mechanical state is transfered into the turbulent motion of the liquid and may act as an active impactor as the shearing of the bubbles which carry the particles to the liquid surface is enhanced. Beside this result it could be qualitative shown that bubbles arise from the liquid fed holes of the Laskin nozzle. This implies that no particles can be generated at the ring side of the jet, in contrast to the existing literature.