(71a) Unbaffled Angled Agitation

In many instances, particularly in biological and pharmaceutical processes for the purpose of cleanliness, it is not uncommon to prefer an unbaffled vessel. The elimination of baffles can make providing optimal mixing difficult because baffles eliminate swirl and promote top-to-bottom motion with axial-flow impellers. To approximate the flow field of an axial-flow impeller in a baffled vessel, agitators in unbaffled vessels are often placed off the vessel centerline. These off-center agitators may be mounted vertically or at an angle to the vertical.

Despite the relatively common use of angled agitators, limited data on these systems is available in the open literature. Building upon a recent analysis of unbaffled angled solids suspension agitation, the current work addresses the issues of turbulent power draw, impeller discharge velocity, flow pattern, and computational fluid dynamics simulation of these systems in liquid-only operation. The effects of the following parameters will be considered.

? Impeller type (pitched-blade turbine and Chemineer SC-3 and HE-3) ? Impeller location ? Impeller diameter to tank diameter ratio ? Impeller off-bottom clearance ? Liquid level ? Mounting angle (focusing on angled mounting with limited vertical data)