Suspension flow behavior and particle residence time distribution in helical tube devices

Abstract Manufacturing of fine chemicals and pharmaceuticals often comprises the handling of solid/liquid suspensions both in upstream and downstream processing. Continuous manufacturing of such products is promising compared to conventional batch production, even though, flow processes in tubular devices usually suffer from particle settling and clogging. The isothermal suspension flow behaviors of various solid/liquid systems, i.e., crystalline l -alanine/saturated aqueous solution, PVC beads/water, and glass beads/water, with up to 10 wt-% of particles were investigated and successfully operated in horizontal helical coil tubes without blockage. The densimetric Froude number is used to describe the flow behavior in the coiled tubes in which three different regimes were observed, i.e., homogeneous suspension flow, moving sediment flow, and stagnant sediment. Empirical correlations based on the tube diameter, the mean particle size, the particle mass fraction, the fluid flow rate, the pulsation characteristics of the utilized peristaltic pump, and the physical properties of the system were developed for the critical densimetric Froude number to define the transition between these regimes. Based on this, the particle residence time distributions (RTD S ) in the different flow regimes were investigated by step-response experiments from 0 to 1 wt-% of PVC particle tracers in aqueous suspension in a horizontal coiled flow inverter (CFI). A narrow RTD S close to ideal plug flow was found. These results enable both equipment and process design in existing equipment on a short-cut model level.