Monodisperse Spray Research Articles

Ultrasonic atomization-a photographic study of the mechanism of disintegration

Existing theories to account for liquid disintegration in ultrasonic atomizers are reviewed and examined in the light of observations of two different 40 kHz atomizers. Photographic techniques including single exposure, high-speed still and synchronized flash high-speed ciné photography were used. Corroborating evidence for a capillary wave mechanism was obtained but disintegration as a result of cavitation effects was also observed. Sonoluminescence and therefore cavitation was detected at all power levels capable of causing atomization. A mechanism for the cavitation effects is proposed. From this the performance of a typical atomizer is explained and the general conditions for obtaining a near monodisperse spray at optimum throughputs are given.

Measuring the mobility of charged aerosols by Schlieren interferometry of Doppler-shifted light

A new method for measuring the velocity of charged particles or droplets moving in applied electric fields is described. It uses a Schlieren system which selects symmetrical plus and minus diffraction orders and allows them to overlap and interfere, so that the best frequency due to the differential Doppler-shift can be recorded at a point in the image plane. The method is illustrated by its application to a monodisperse spray of electrically atomized kerosene, using a He-Ne laser as the light source. Its advantages are discussed and its range is assessed theoretically.

The Generation of Monodisperse Aerosols by Means of a Disintegrated Jet of Liquid

A thin jet of liquid issuing from a nozzle at a high velocity disintegrates spontaneously into droplets under the action of surface tension. A periodic disturbance of the jet can be used to control the disintegration so as to make all droplets of the same size. A system for generating monodisperse sprays according to the principle outlined above has been designed and built. The jet is modulated by axial vibration of the nozzle, which is mounted at the center of a membrane. The membrane is vibrated by means of electrostrictive elements. Droplets in the diameter range 40–15 μ have been produced at a vibration frequency of 20–300 kHz. The stream of droplets has been analyzed in several ways. A jet of air perpendicular to the droplet stream has proved to be of special value. Several air jets, pulsed in suitable phase relations, are utilized to disperse the stream of droplets and to prevent the droplets from coalescing during the drying phase of the aerosol generation.

Production of Monodisperse Sprays

A technique for producing monodisperse sprays is described. The technique makes use of Rayleigh's criterion for the breakup of capillary jets by mechanically vibrating a number of uniform size capillary needles arranged in parallel. It was used to produce sprays in the size range of 290–950 μ, but in principle there is no reason why this range cannot be extended. The regime of spray sizes where drop coalescence is likely to take place is delineated, and methods of minimizing coalescence are described.