Dynamics of destabilization of food emulsions. Measurement and simulation of gravity driven particle velocities in polydisperse dispersions
Abstract
A new experimental technique based on the application of population balances and measurement of size specific number densities has been developed which measures the average hindered terminal velocity of every particle size in a polydisperse suspension or emulsion. The present technique overcomes classical difficulties associated with both experimental and theoretical approaches and is capable of determining all particle speeds from the dilute limit to the dense over the entire range of polydispersity. Results for many emulsions show good agreement with well known predictions in the dilute limit. Even more significantly, substantial deviations in particle speed are measured in dense systems for small particles while the large particles are accurately represented with current correlations. These results contradict the trends predicted by dilute polydisperse theories of Batchelor and may be attributed to multi-body interactions neglected in his analyses. The technique is capable of measuring the effects of numerous additives, such as glycerin, salts, and gums on creaming dynamics. A new polydisperse correlation which accounts for the observed effects is proposed based on Batchelor's dilute polydisperse correlation and the Richardson and Zaki equation. The empirical constants in the proposed correlation were determined with a least squares fitting of the experimental data. The goal of this endeavor is to develop a universal correlation which can predict the creaming behavior of any homogeneous emulsion with various types of additives. Further, the correlation is useful for incorporation into multi-phase flow models of polydisperse suspensions in which the hydrodynamic interaction of specific particle sizes with the continuous phase is required. The correlation was used to simulate the evolution of a batch dispersion to generate food shelf-life predictions. The governing batch continuity equation was solved with the method of characteristics and shown to form sedimenting or creaming zones. The simulation predicted the speeds of these zones and determined the particle flux into the cream, thereby determining the cream particle distribution. This approach contrasts current empirical shelf-life techniques used in the food industry by providing quantitative predictions of emulsion behavior based on system specific parameters.
Degree
Ph.D.
Advisors
Ramkrishna, Purdue University.
Subject Area
Chemical engineering|Food science
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