Daniel Bonn (University of Amsterdam, the Netherlands). What Determines the Drop Size in Sprays?

Sprays are generally formed from the breakup of liquid jets or sheets. We investigate the different parameters that determine the characteristic drop size and its distribution i the breakup of sheets. We vary both the spraying parameters, such as the pressure and geometry of the nozzle, and the fluid parameters, such as viscosity and surface tension. The combined results show that the drop size is determined by a competition between fluid inertia and surface tension, which allows for the prediction of the drop size from the Weber number and geometry of the nozzle.

 

The size distribution is found to be described by a compound gamma distribution with two parameters, n and m, with the former setting the ligament corrugation and the latter the width of the ligament size distribution. Values for m indicate that the size distribution depends on the nozzle type, and values for n show that, for all nozzles, ligaments are very corrugated. Using high-speed photography of the sprays, the parameters m and n can be directly measured and indeed govern the drop-size distribution.

 

Using this knowledge, we are not attempting to make sprays with uniform drop sizes by creating smooth ligaments that all have the same size. This however turns out to be complcated by drop coalescence.