side entering mixer offset from center

[wydim]

***previously posted in the "storage tanks" forum***

Hello all,
This is my first post to the forum.

We're installing a side entering mixer into our 15 milk silos that we're manufacturing. According to James Y. Oldshue, in his book : FLUID MIXING TECHNOLOGY (see attached scan)

"if the impeller is rotating clockwise, the mixer must be angled to the left (fig. 1-23) [offset from the center]"

is the corrolary true : "but if the mixer is offset to the right, make it rotate counter-clockwise and mirror the blades (to keep having the flow going forward, instead of pulling the fluid)

For various space constraints (interference with side manway cover), we want to install the mixer angled to the right. Can I wire the motor to rotate counterclockwise and manufacture a mirror blade impeller ?

regards,
Dimitri

 

[djhurayt]

I'm sorry I don't have your answer, but my first thought was "seems reasonable". But then I got to thinking that water naturally swirls down the drain in the opposite direction on the bottom half of this rock. So not sure if this is involved or not, hope somebody chimes in.

 

[IFRs]

Have you contacted the mixer manufacturer?

 

[EdStainless]

DJH, water swirls based on the original energy input, it doesn't matter where in the world you are.

It depends on the motors, check with the supplier.

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P.E. Metallurgy, Plymouth Tube

 

[djhurayt]

Ed, are you sure.

So if I have a bucket of water with a corked hole in the bottom and I remove the cork in the northern hemisphere the water will swirl in a clockwise direction, and in the southern hemisphere it will swirl counterclockwise.

This is just a farce? I was taught that this was due to the spin of the earth and is the same reason weather systems tend to go west-to-east in the north and east-to-west in the southern hemisphere.

I just wondered if this natural rotation tendency would play into the OPs desire to mix in the opposite direction. ???

 

[EdStainless]

If you give slight stir with your finger then pull the cork it will continue to swirl the direction that you started it. Either way in either in either hemisphere.

The offset for the mixer has to do with combined forces on the mixer. Setting as they suggest reduces the side loading on the mixer.

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P.E. Metallurgy, Plymouth Tube

 

[Compositepro]

The Coriolis effect is very small and will be swamped by other factors, like which way the propeller is turning.

https://www.youtube.com/watch?v=i6I21gadHCU

https://www.youtube.com/watch?v=cLUXALnzSZI

 

[wydim]

hello All ! thanks for your replies.

yes, I also believe (know) that coriolis effect is negligible compared to the other forces at work in this example.

@IFRs, lol, WE are the mixer manufacturer. Actually we are a S.S. pressure vessel and silo manufacturer. We happen to have a standard side mixer that we always install correcty in our milk silos. Now, I want to install it offset to the right.

So, does anybody have a clear answer?

regards,

 

[robyengIT]

everything has to be "mirror"

 

[chicopee]

As a manufacturer, wouldn't it behoove you to have a pilot plant and test modifications to your vessels?

 

[EdStainless]

Check with your motor supplier.

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P.E. Metallurgy, Plymouth Tube

 

[wydim]

@chicopee, we're not a big company and it's not like we're launching a new product where all phase of product design would be followed (testing, prototypes, scale up, etc.... We are in the custom business so every project has an estimate cost, a budget and a tight schedule. Unfortunately, that was not in the budget. And the consequences of getting it wrong are not of great significance (because the cooling of the milk will happen anyway because the client requested more than enough amount of cooling dimple jacket.

@EdStainless. What do you mean, "check with the motor supplier" ? Our motor supplier, SEW eurodrive knows even less than us in the mixing business. They just supply a torque to a shaft. I've send inquiries to "real" mixer manufacturers. Still waiting for their answers.

thanks all,
Dimitri

 

[djhurayt]

I suspect Ed was talking about the wiring of the motor to get it to run backwards

 

[wydim]

@djhurayt, okay, but that's a no brainer. I thought it was assumed in my question.

 

[IFRs]

I agree that the Coriolis force is small but what the heck - why not take advantage of it? Sometimes every little bit helps. If there is no cost or penalty and there is no other harm you get a free and potentially a small benefit. If it can't be done or it raises the hackles of someone somewhere, give it up without remorse. Your initial question was not so much should you change the direction of your normal orientation but should the blade spin be reversed also. In my opinion yes, the blade should push the liquid the same way. If this means making a mirrored impeller, so be it. The question then is, if the mixer is angled the other way, should the rotation and impeller be changed. I think yes. This makes sense from visualizing the flow and swirl pattern - to get good mixing and liquid movement it "feels right" to have the blades twirling the other way. So, this boils down to this: don't change your standard because of the Coriolis effect - it costs too much for little benefit. But if you are changing the orientation of the mixer for other reasons, I think you should counter-rotate a mirrored impeller.

 

[chicopee]

Have you done any research about mixing simulation software that could be pertinent to your OP? Altho not in my areas of interest, I have read about such simulation software in Chemical Engineering periodocals.