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Author Topic: Tech News. Automation, Engineering, Environment Etc  (Read 113661 times)

Reelya

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Re: Tech News. Automation, Engineering, Environment Etc
« Reply #2100 on: March 26, 2020, 03:01:18 am »

It's definitely an interesting engineering exercise.  First of all, despite what the video says, it's not a completely symmetric situation: there are real differences between spinning the inner screw versus spinning the outer shaft which can be detected by a difference in the pressure distribution in the material being moved - rotating reference frames are NOT inertial so it is possible to tell if you are in a rotating frame or not.  One key difference is that in the rotating case, the bulk material exits with a notable angular velocity.  This means the transfer of energy is from different mechanisms.

NOTE: none of this means one way is "better" than the other - it's just saying there are real physical differences between the operating mechanics of both machines.
What if the entire machine is loaded onto a platform that's spinning opposite the case? Then from your point of view, it's the case that's static and the screw is spinning again? :P

McTraveller

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Re: Tech News. Automation, Engineering, Environment Etc
« Reply #2101 on: March 26, 2020, 07:28:45 am »

Ooh nice: from the perspective of an inertial frame the case is stationary but the platform and screw are rotating - this is actually a third configuration.  We have now listed:

1. Traditional:  "bulk material" and platform and case in the same inertial frame, screw rotating.
2. "New": bulk material, platform, and screw in the same inertial frame, case rotating.
3. "Reelya's crazy newness":  case in an inertial frame, the bulk material and platform and screw in the same rotating frame.

I think there are these other two configurations to round it all out:
4. Case, bulk material/platform, and screw all in different rotating frames.
5. Case and screw rotating, bulk material and platform inertial.

Actually number 5 is the same behavior as the traditional.  Which is interesting.  Which leads me to believe: technically if you have a rotating case with scoops, you don't need the internal screw at all (although for solid materials it helps a lot). In fact, rotating case with inlet scoops and no screw is a just low performance turbopump.


EDIT: If the case is rotating relative to the bulk material, the scoops create a ram pressure effect due to the relative motion.  This pressure is the force that drives the material up the pipe.  In this configuration, the "pressure" of the material against the screw is a reaction, it is not the "driving" force - this can be shown by a free body diagram.

EDIT: IMAGES!!!  If you "unroll" the screw, you get a wedge.

Traditional screw pump: the wedge moves, creating its own ram pressure to raise the material:
Spoiler (click to show/hide)

"New" screw pump:  the wedge doesn't move, so something has to push the material up the wedge.
Spoiler (click to show/hide)

When the case is spinning, the "push" for this comes from the ram pressure of the scoop moving.

What these diagrams can't show is that the scoop version can only make pressure in the "wedge" direction by first making pressure in the tangential direction (into or out of the page for these drawings).  This tangential motion requires a radial pressure gradient to keep those particles moving in a circle; this pressure gradient is NOT present in the traditional screw, because the motion of the wedge is always in the "wedge" direction - it doesn't need tangential motion.

This is a fun digression   8)
« Last Edit: March 26, 2020, 09:40:03 am by McTraveller »
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Bumber

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Re: Tech News. Automation, Engineering, Environment Etc
« Reply #2102 on: March 26, 2020, 03:33:48 pm »

We must demand that Toady One implement "new" screw pumps alongside the existing ones.
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Max™

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Re: Tech News. Automation, Engineering, Environment Etc
« Reply #2103 on: March 26, 2020, 09:53:14 pm »

Yeah, taking the idea apart into a wedge and a wall was why the claim it made less dust seemed plausible, that tangential pressure is going to get applied against the other moving materials which are less likely to crush each other than the total forces coming exclusively from the wedge.

I suspect that's the same reason stuff comes out along the rim when the screw passes it and cycles around normally while spinning the case makes it scatter from the entire rim, all the rest of the material is lifting/scattering vs the presence of the screw causing material to pile up and fall off.
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