Title: On-line Process Rheometry using Oscillatory Squeeze Flow

Authors and Affiliations:
David Konisgberg¹, T. M. Nicholson¹, P. J. Halley ¹ P. Koria², E. Owen³, (presenter) P. K. Bhattacharjee4 and T. J. Kealy4

1 – Department of Chemical Engineering, The University of Queensland, St. Lucia, QLD, Australia
2 – GlaxoSmithKline, Consumer Healthcare Technical, GSK House, TW8 9GS, UK
3 – GlaxoSmithKline, Consumer Healthcare R&D, Surrey, KT13 0DE, UK
4 – Rheology Solutions, OLR Group, Bacchus Marsh, Victoria, Australia

 

Abstract

Manufacturing operations in a variety of industrial sectors routinely encounter complex fluids in flow processes. Rheological characterisation of such fluids is commonly employed for process and quality control in these industries. In a typical process operation small quantities of the process fluid are intermittently sampled for rheological measurements and decisions on the efficiency of the process or the quality of the product are taken based on information provided by these measurements. However the large number of steps involved in this approach increase the processing time in addition to invoking inconsistencies that lead to significant variability in the measurements. These complications often make effective process/ quality control using rheometric techniques difficult.

The effectiveness of control strategies involving rheological measurements can be improved if measurements are made online during processing and the sampling steps are eliminated. However, online instruments capable of providing sufficiently detailed rheological characterisation of process fluids have so far been difficult to develop. Commercially available online instruments typically provide a single measurement of viscosity at a fixed deformation rate. The dependence on a single pre-determined shear rate restricts the instruments from indentifying changes in the product or the process that permit the viscosity at the chosen shear rate to remains unaltered.

We introduce an OnLine Rheometer (OLR) that uses small amplitude oscillatory squeeze flow to measure the viscoelastic properties of process fluids “on-line” under typical processing conditions. We demonstrate that by carefully choosing the measuring geometry and the amplitude of oscillation the frequency response of a prototypical non-Newtonian fluid (2.5% carboxymethyl cellulose) can be measured “on-line” in a process pipe, with an accuracy that rivals that of modern laboratory rheometers. We also compare our results with other techniques that are typically used for process rheometry for critically evaluating the utility of the OLR technology for advanced process and quality control. We also discuss the application of the OLR technology to a process for manufacturing toothpaste.