The development of a novel probe for the in situ measurement of particle size distributions, and application to the measurement of drop size in rotor-stator mixers.

摘要

The development of a novel instrument for the in situ measurement of particle size distributions in the size range of 3 to 200 m m is presented. The system uses high magnification optics, housed in a stainless steel probe, designed to be inserted into a process stream or vessel, where images of the dispersed phase particles are recorded. A pulsed light source is used to freeze the motion of the particles in the field of view, and present an image of the dispersion onto a CCD camera chip. The images are digitized and stored for later processing. Automated image analysis routines have been developed for extracting particle size information from the acquired images. An extensive validation of the instrument has been performed for spherical particles, which have produced several important findings. First, a size bias in the depth of field exists which favors larger particles. An experiment procedure developed for the direct measurement of depth of field size biases. Additionally, the behavior of the instrument is dependent on the environmental conditions, such as dispersed phase concentration and the difference in index of refraction between continuous phase and dispersed phase.; The utility of the instrument is displayed by the in situ measurement of drop size distributions of dilute liquid-liquid dispersions formed in rotor-stator mixers. The experimental work offers the ability to obtain novel data, since little is known of the operation of this class of mixers. Five mechanistic models are examined for their ability to predict scaling of drop size in rotor-stator mixers. In addition, an experimental estimate of the energy dissipation rate is presented. Based on the estimate of the energy dissipation rate, the size of the drops appear to be on the order of the Kolmogorov length scale. This suggests drop breakup is in a transition region between breakup by inertial stresses and breakup by viscous stresses arising from the turbulence.