A new apparatus for the production of monodisperse sprays at high flow rates

A spray generator was constructed for the production of monodisperse liquid sprays at industrially relevant liquid how rates. The operation of the generator is based on the Rayleigh-type breakup of multiple liquid jets. Laser drilled nozzle holes (diameters 41 or 76 mu m) in the nozzle plate (diameter 105 mm) produce 613 individual laminar liquid jets; liquid mass flow rates of up to 170 kg/h are thus obtained. The breakup of these liquid jets is controlled by a piezoceramic oscillator which is driven by a square wave excitation signal. The operation of the spray generator was characterized using video imaging. The spray generator provides a well controlled monodisperse spray with a fairly wide operation envelope with respect to nozzle Reynolds number and wave number (Re=600-1200, k=0.3-1.0). The liquid jet velocities at different positions of the nozzle plate were found to be equal. Furthermore, the excitation proved to affect all the liquid jets emerging from the nozzle properly. The relative standard deviation of drop diameters in the spray was typically 2-4%. With increasing downstream distance from the nozzle plate, the interaction between the spray and the surrounding gas leads to the loss of monodispersity through collisions and subsequent coalescence of neighbouring droplets in the jets. Some preliminary investigations about the influence of an amplitude modulated excitation signal on the operation of the spray generator were also conducted. Copyright (C) 1996 Elsevier Science Ltd.