Drag of non-Newtonian fluids on assemblies of spheres in tubes: Potential application to modeling of two-phase flow in aseptic food processing

Continuous aseptic processing of low-acid foods containing particulates has not received regulatory approval owing to the present inability to predict survival rates of the lethal Clostridium botulinum bacterium in particle cold spots during such a process. Mathematical modeling is a valuable tool that provides important information regarding complex processes without the expense of actual process runs. One of the present obstacles in modeling of aseptic processing of low-acid particulate foods is the lack of a reliable estimator of particle residence times in holding tubes of aseptic process systems. The drag force of the liquid phase on the suspended particles is responsible for their motion along the holding tube, and thus determines their residence times. Therefore, a reliable expression for drag coefficients for particles suspended in non-Newtonian tube flow (a feature of continuous aseptic processing) is necessary for use in comprehensive mathematical models simulating particle motion in the holding tube. The objective of this dissertation was to develop such an expression for the drag force on spherical particles suspended in non-Newtonian tube flow.;The flow of a suspension of spherical particles relative to the carrier liquid was approximated by closely packed, symmetric assemblies of rigid spheres held stationary in fluid flow. An apparatus was assembled to enable direct measurement of the drag force of viscous solutions of sodium carboxymethyl cellulose (CMC) on the sphere assemblies inside a tube. The drag force measured was expressed as a dimensionless drag coefficient per sphere. An empirical correlation between the drag coefficient (C...