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Magnetic stirrer - no vortex
submitted about 8 years ago by deckartcain

Hello guys. I tried googling my way to this one, but I can't for the life of me seem to find a clear answer.

I was trying to mix in a 1l flask, but I can't get a vortex going - only about half of the solution is mixing.

Is it possible to increase the functionality somehow? Larger stirring rod?

Relevant specs goes as follows(from manufacturer):

Stirring Volume: 0~2000mL

Stirring Speed 0~1250rpm

I'm using a rather small stirbar now.

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4 points
 
by nashvortexabout 8 years ago

Large stirbar. Start slow and slowly increase the speed.

It is possible that you magnetic stirrer just doesn't have enough current to take the load of mixing a large volume.

3 points
 
by deckartcainabout 8 years ago

Alright. Thanks for the reply. The viscosity of the VG seems to add to the difficulty of mixing. I tried heating the mix to 105 degrees with no concernable difference.

2 points
 
by browbrowbrowbrowabout 8 years ago

Never mixed my own juices, but do work in an actual lab and create media and have to work with homogenizing glycerol and thick powders. It can help if you first pick up the flask and swirl it in the direction it is going to vortex, then like u/nashvortex suggested starting with a lower RPM. Adding a little bit of your solution in at a time should also help. Step it up gradually as the vortex keeps it up.

1 points
 
by deckartcainabout 8 years ago

I'll retry with these advices in mind for sure. The cylinder I have is a rather tall one. Would a shorter but wider beaker with similar volume be easier to achieve a vortex in?

2 points
 
by Boziakabout 8 years ago

Heating the vg will help. Like they said, start slow and work your way up. I have one, and I never get a full vortex, but I do see the full batch mixing.

1 points
 
by deckartcainabout 8 years ago

I'll definitely try adding incrementally from now on. I was also accepting of vortex less mixing, and have done it with success in smaller batches with different lab ware, but I was getting an obvious top layer which had no activity. Just out of curiosity, at which temps do you mix?

2 points
 
by Boziakabout 8 years ago

I have a heating mixer. I usually set it to 60 degrees Celsius. My mixes usually end up 80/20 vg/pg ratio. I will get a good concave up top, but the vortex never reaches the magnet. I start at 25 rpms. And incrementally increase it every minute or so. The bigger magnets usually don't go over 250 rpm, while the smaller one I can get to about 750 before they spin off the magnetic connection with the base.

1 points
 
by deckartcainabout 8 years ago

What's your experience with the bigger ones? Have you tried mixing liter batches? What kind of instruments would you use?

The magnet I have take up about 20% of the diameter of the beaker in this setup.

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