Residence times of multiple particles in non-newtonian holding tube flow: Effect of process parameters and development of dimensionless correlations

Abstract

A study of residence times of multiple spherical particles suspended in aqueous solutions of carboxymethylcellulose (CMC) during pseudoplastic flow through a commercial size transparent holding tube system is presented in this paper. Polystyrene spheres were used to simulate the food particles. The parameters considered in this study were fluid viscosity, 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 concentration and flow behavior index; for the dimensionless standard deviation of the residence times, particle size to tube diameter ratio was also incorporated in the correlation. The results showed that viscosity, flow rate and particle concentration affected the mean, minimum and standard deviation of the residence times while particle size affected only the standard deviation of the residence time significantly (α = 0.05). It was also observed that the mean particle residence times were close to the mean fluid residence times while the minimum particle residence times were much larger than the theoretical minimum (center line) fluid residence times. The ratio of minimum to mean particle residence time was between 1.06 and 1.16. Within the range of parameters 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 buoyant).