Newbie needing advice for prototype testing 1

[td24]

Want to test a concept and need some help

I need to test whether or not I will be able to properly mix liquid substances within a cylindrical container that is about 6 feet in diameter x 6 feet tall. The one issue with mixing within this container is that there is a cylindrical piece that runs vertically down the middle of the entire container

I think that having two separate radial impellers on the left and right side of the vertical piece will be able to properly mix the contents. Would love feedback on this theory...

If this theory seems like a good way to go, what suggestions would you make for creating a simple and relatively inexpensive module to test if it would properly mix the contents of the container?

 

[Compositepro]

I on the fluid properties but, assuming that horsepower is kept constant, one impeller is probably sufficient. A radial impeller will induce a circulation around the container.

 

[GregLocock]

Can you work out the dimensionless scaling for your mixing and then build a pint sized rig with the relevant dimensions and viscosity etc?

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[tomwalz]

Get a 5 gallon water bottle from the lunchroom.
Get a cylindrical vase from Hobby Lobby or similar.
Get glitter
I would use air because I have it.
Put end of air hose on stick so you can hold it where you want it in the water.
Turn on air.

Admittedly this is kind of a cheap, jury rig but it will give you some idea fast and for darn little money. If you don’t have compressed air you can blow in the tube. If you have compressed air turn it on very, very slowly.

Set a camera up next to it so you get video. Glitter takes a long time to settle out. If you have to report to a committee do several different runs with different colored glitter.

The $50 Rule

I was once in a meeting with five of my employees. The discussion was whether to buy a $50 magnet to sort tungsten carbide from tumbling media. After about 15 minutes the discussion was turning into an argument. It was then that I realized that I’d spent much more than $50 listening to people argue.

Now we have the $50 rule. If you have an idea you’re not sure about then spend a couple of bucks, cobble something together and get some data.


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[RolMec]

I'd put forward some more questions:
a) What is "properly", and is there a parameter / benchmark to this?
b) How fast should the process be finished?
c) Is the mixing reversive, will the mixture segregate after stopping of the impeller?

and also as a sidethought:
Tests on mixing of solutions t. b. done if possible with the original ingredients, due to their physical etc. properties they might behave unique / at least otherwise than say glitter in water.
Testing on a scale is good! Why not use a speed controlled hand tool (screwdriver) & tinker on some impeller. To make it like look a real thing. There might even be something t. b. found in a craft or gift shop. There's fun in this, it seems, and it will look good on your shelf of experiences...
Regards
R.

 

[moltenmetal]

If the vertical cylinder running down the centre of the tank is a) of a decent diameter and b) open at the top and bottom, and the tank has a lid, all you have to do is turn it into an "airlift" type mixer arrangement. Put a couple axial flow impellers (marine props will do fine and are very cheap) on the same shaft, mounted along the centre axis of the weir tube from the top of the vessel, such that they pump upward and draw liquid in from the bottom. Make sure they can generate enough head to spill the contents over the top of the cylindrical weir. You will then set up a circulation pattern in the rest of the tank.

If you're trying to disperse two liquids in one another, or to wet out a floating solid, this arrangement may not generate enough shear in the outer annular portion of the vessel, but if it's just liquid/liquid blending it should work fine.

 

[IRstuff]

The only question, then, is the time element, and how well do you really need it mixed? You'll need to play with the impellers' vertical positions, to ensure that the fluid will circulate properly. Rather than putting them on the bottom, they probably should be midway up the central shaft. Another option is two sets of counter rotating impellers, one set placed 1/4 from the top and one set 1/4 from the bottom. Even with that, near the surface of the outer wall and at the corner at the bottom might not get thoroughly mixed. A single set of impellers could potentially just set up a relatively laminar circulation in the middle of the tank, which would get everything moving, but not necessarily mixing.

Tom Walz' idea of using air would be a good alternative, since air into water tends to be very turbulent.

TTFN
faq731-376

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[Dougt115]

Your design will work. I have used a similar design, but only one impeller, for mixing rocket fuel in 600 gallon batches.

A couple considerations:
Viscosity, thick fluids will be harder to thoroughly mix near corners and sides. You may want to have a container that more closely matches the mixing blades. Or blades that match the container.

Impellers should be designed to counter a fluid current. You don't want to start a whirlpool.

A single impeller may be all that is required and will simplify the setup, cleanup and repairs.

A design like the Kitchen Aide mixer is an efficient system.

A simple test would be, buy the Kitchen Aide and give it a try. If you use non-toxic substitutes with similar properties the better. All you would have to do is change the design of the impeller to make room for the cylinder in the middle.