Sedimentation behavior of suspensions in milliflow reactors

Abstract

The increasing industrial interest in performing heterogeneous solid–liquid reactions in tubular reactors requires control over sedimentation and accurate data on the solid velocity in order to optimize residence time distribution. In this research, concentration profiles, velocity profiles and the minimum suspension speed of non-interacting solids in milliflow reactors are determined via image analysis and particle image velocimetry. First, the five different flow regimes are identified. Then, the minimum suspension speed, ensuring a homogeneous/pseudo-heterogeneous flow regime is observed to be between 0.7 and 1 m/s depending on liquid and solid properties. Reducing the liquid viscosity and density difference, decreases the minimum suspension speed. Based on the free settling velocity, the Reynolds number to avoid sedimenting of particles can be calculated. The identification of minimum suspension speed and Reynolds number were found to be the determining factors enabling broader application of heterogeneous solid–liquid reactions in milliflow reactors, in academic and industrial environments.