RESIDENCE TIMES OF MULTIPLE PARTICLES IN NON-NEWTONIAN HOLDING TUBE FLOW - EFFECT OF PROCESS PARAMETERS AND DEVELOPMENT OF DIMENSIONLESS CORRELATIONS

A study of residence times of multiple spherical particles suspended i n aqueous solutions of carboxymethylcellulose (CMC) during pseudoplast ic flow through a commercial size transparent holding tube system is p resented in this paper. Polystyrene spheres were used to simulate the food particles. The parameters considered in this study were fluid vis cosity, suspension flow rate, particle size and particle concentration . Equations to predict dimensionless mean and minimum residence times were developed as a function of particle Reynolds number, particle con centration and flow behavior index; for the dimensionless standard dev iation of the residence times, particle size to tube diameter ratio wa s also incorporated in the correlation. The results showed that viscos ity, flow rate and particle concentration affected the mean, minimum a nd standard deviation of the residence times while particle size affec ted only the standard deviation of the residence time significantly (a lpha = 0.05). It was also observed that the mean particle residence ti mes were close to the mean fluid residence times while the minimum par ticle residence times were much larger than the theoretical minimum (c enter line) fluid residence times. The ratio of minimum to mean partic le residence time was between 1.06 and 1.16. Within the range of param eters studied, the suspensions were very homogeneous and no channeling phenomena were observed. This uniformity of the suspensions could be attributed to the range of particle concentration analysed (4-10%, v/v ) and the ratio of particle to the carrier density (nearly neutrally b uoyant).