Developing a non-intrusive measuring technique for determining orthokinetic agglomeration rate constants

A non-intrusive technique has been developed for measuring agglomeration rate constants (beta(0)) in a constant shear field. A particulate suspension with a mean particle diameter, d, of about 10 mum is introduced in an optically accessible cylindrical Couette flow device. The suspension is illuminated by means of a pulsed laser and observed with a CCD camera. The recorded images are analysed off-line to determine the particle number concentration and a measure of the particle size. The time evolution of these quantities is fitted to an agglomeration rate law, from which the agglomeration rate constant is subsequently derived. By varying the rotational speed of the outer cylinder, different shear rates can be applied to the suspension. The full shear rate dependence of the agglomeration rate constant can be measured this way. Test results show that the set-up is well suited to determining particle concentrations, while only relative particle size information could be obtained. The measured signal shows a linear response to the suspension concentration and obeys the expected Poisson statistics. One set of agglomeration rate constants, measured at seven different shear rates between 15 and 55 s(-1) was obtained. A distinct maximum for beta(0) was found at a shear rate of 30 s(-1) which will be the subject of further study.