Phase Doppler sizing of optically absorbent single- and multicomponent liquid droplets using semiconductor devices

Abstract

After a successful application of the phase Doppler technique to homogeneous transparent or opaque dispersed media, it was the aim to attain with this method simultaneous size and velocity measurements of real process fluid droplets that are optically absorbent and/or inhomogeneous, in order to open the way to in-line measurements for process control. On the basis of previous experiments and the idea of using a larger wavelength of 830 nm (semiconductor laser) instead of 488 nm (Ar ion laser), ambiguous phase difference-particle diameter relationships due to absorption were avoided. For optically absorbent homogeneous liquid droplets, the Mie theory alone proves to be an indispensable means for selecting the suitable PDA set-up parameters. For inhomogeneous liquid droplets, the Mie theory and Mie scattering computer programs can be used to describe and understand their scattering behaviour. Computer aided PDA (CAPDA) measurements thus open the chance for in-line process measurements in real process liquid spraying.