Swirling vs. Mixing: The Right Fluid Motion Matters

INDCO

The liquid in your mixing tank is flowing rapidly and there is an unmistakable vortex from your center-mounted mixer.   So why are the results of your mixing process falling short of expectations?  If you’re working with light viscosity materials the problem may be that all that liquid movement is swirling vs. mixing.  In the design of mixing systems we quantify the volume of liquid pumped by a given impeller and also consider the flow pattern, or where that pumped liquid moves through the vessel.

A brief review of the definition of mixing reminds us that true mixing is the change in relationship between two theoretical “particles” as they experience turbulence from the impeller.  A center-mounted mixer in a low-viscosity application can result in near uniform circular movement of the entire batch in the tank, thereby minimizing true mixing.  Two common resolutions to swirling are angular mixer mounting and tank baffles.  Mounting the mixer shaft at a compound angle 10-20 degrees from vertical and at the same angle from the tank wall results in a turbulent flow pattern that ensures good mixing.  If a vertical center-mounted configuration is unavoidable or impractical tank baffles can be used.  Depending on the tank size, three or four baffles approximately 1/12th the tank diameter causes eddy currents which induce turbulent flow and improved mixing.

INDCO customer service representatives and engineers are ready to help you with your mixing process questions.  From batch size and viscosities to selection of the right horsepower industrial mixer and impeller we can help.  Call us today!