Mixing system: Wand Mixer
Mixing biocontainer: 200 L Mixer biocontainer
Application mixing type: Powder-liquid
The Wand Mixer is a compact and non-invasive single-use mixing system. The heart of this system is a mixing biocontainer incorporating an innovative top-mounted impeller capable of providing efficient mixing for powder-liquid and liquid-liquid mixing applications. The impeller comprises a rotating wand inside an inert polymer sleeve, and is designed to ensure low particle shedding and total containment while serving effectively in a wide variety of mixing tasks.
Introduction
Powder-liquid mixing is a common requirement in biopharmaceutical processing. In order to optimize mixing efficiency for powder-liquid applications, the Wand Mixer is available with a large, diagonally mounted helical mixing wand.
In this experiment, a Wand Mixer ability to suspend a very high powder load was tested. The powder chosen was diatomaceous earth, a fine, inert, and insoluble, powdered filter medium that is light and fluffy when it is dry, yet forms a dense mud when mixed with water.
Materials and methods
A 200 L Wand Mixer mixing biocontainer was filled with ~ 180 L of water, and mixing speed was set to 250 rpm. Diatomaceous earth powder (d = 0.22 kg/L) was then added in increments up to a total weight of 22 kg. After each increment, the mixer was shut off and the suspended powder was allowed to settle into a dense, compacted mud at the bottom of the mixing biocontainer over several hours. After the powder had settled, mixing was restarted, and the impeller’s ability to resume mixing was observed.
Results
When initially added, the dry diatomaceous earth powder was dispersed completely within a few seconds of completing the add; the limiting factor to faster dispersion was the speed of dispensing the dry powder. Once the full 22 kg had been added, the Wand Mixer provided sufficient agitation to maintain all of the powder in suspension.
After the powder had settled, complete resuspension of the slurry took only 30 s even at the highest load. The times taken for full resuspension are shown in Figure 1. At no time during this experiment did the mixer’s wand impeller stall or otherwise hesitate.
Fig 1. Time taken for full resuspension.
Conclusions
The mixing action of the Wand Mixer is capable of high mixing efficiency without stalling in high-load powder-liquid applications. The maximum load tested, 22 kg of diatomaceous earth, was easily resuspended within 30 s.
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