Investigation of Cloud Height in a Stirred Tank

The goal of the study was to determine the effects of particle size, particle density, particle concentration, fluid viscosity, tank size, and impeller speed on the cloud height of particles suspended in a stirred tank. Lab and Pilot-plant scale experiments were performed.

Hydrofoil impellers with 8.5 cm and 18 cm diameters were used in the lab and pilot-plant scale respectively. Particles tested included: aluminum, sand, urea formaldehyde, melamine, garnet, steel, glass, and acetal spheres. Plexiglas flat bottomed tanks with 28.3 cm and 61 cm diameters were used for small and large scale experiments. Both tanks were configured with 4 baffled, impeller diameter and impeller clearance equal to one-third the tank diameter, and baffle width equal to one-twelfth the tank diameter. Cloud height was measured at impeller speeds (RPM) ranging from nearly just suspended speed (NJS) to 2355 RPM for the lab scale and 800 RPM for the pilot-plant scale with particle concentrations of 5% to 30% by mass..

A regression analysis was used to estimate the influence of each factor on cloud height. The analysis determined impeller speed and tank diameter to have the most influence on cloud height. Particle density and size also have a significant effect on cloud height. Viscosity has a greater effect on the cloud of smaller particles. A correlative model for cloud was developed based on the experimental factors tested. Future work will include investigating the effect of viscosity on large particles and revisiting the NJS particle size breakpoint phenomena at higher viscosities.

Title: Investigation of Cloud Height in a Stirred Tank

Authors: Alexander Hesketh, Mariah Soyring, Anthony Horvath, Diane Severino, Liam Lafferty, Greg Van Ommeren

Sponsors – Dr. Etchells and Dr. Hesketh