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In the present investigation, Taylor's analysis of the axial dispersion of a solute in a Newtonian fluid undergoing laminar flow through a circular tube was applied to dispersions of colloidal particles, in which effects of size exclusion, inertial and colloidal forces, and wall retardation must be considered. The results indicate that the product of the particle Reynolds and Peclet numbers determines the importance of the inertial forces on both the effective axial diffusion coefficient and the height of a theoretical plate. The height of a theoretical plate as a function of the eluant ionic strength and average velocity, particle diameter, and tube diameter was determined experimentally. Close agreement with the numerical calculations from the diffusion equation was obtained. The height of a theoretical plate was found to attain a maximum value when the product of Reynolds and Peclet numbers was approximately 10.5.

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Acoustic Attenuation Spectroscopy (AAS) is a powerful technique for the measurement of Particle Size Distribution (PSD) of concentrated colloids-in most cases without the need for sample dilution, i.e. at process conditions. While AAS has been used successfully in the laboratory, it has not been widely employed for Process Control purposes. This paper describes a new flow-through (Process Online) measurement approach that can make AAS into a suitable Process Control tool for widespread use in most industrial production settings, in particular for PSD measurement and control. This approach basically consists of splitting ultrasonic sound waves by using stepped reflectors and/or transducer delay rods which provide multiple measurement gaps without the use of moving parts.