Help! Water-filled cylinder with rotating middle separator

Discussion in 'The Projects Forum' started by KellyGates, Mar 4, 2014.

  1. KellyGates

    Thread Starter New Member

    Mar 4, 2014
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    Hi all! I know that this is going to be one of "those" posts where somebody who knows nothing asks for help, but I really need it. I teach high school kids (math) and one of their projects involves separating two materials. One will float and the other material will not. They came up with pouring the materials into a water-filled cylinder and then having a middle piece that rotates via motor to separate the cylinder as a means of separating the two materials. It doesn't have to form a seal, as the materials are large. They, then, need to pump out the water and be able to remove the bottom of the cylinder to get the sunk materials out, and then rotate the middle separator again to get the top (previously floating) materials to fall out. I am trying to teach myself about circuits and electronics, but I am a super novice and am not learning at the pace required to be able to help them. So, I would appreciate any advice you can spare. Thanks!

    Also... if you could write any responses as if you are speaking to a three-year-old who knows nothing about this stuff, it'd be appreciated.
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Do you really require them to physically build this "device"?
    Seems just as much mechanical as it does electrical..

    Obviously water and electricity are never a good mix.. Especially when the "educator" is just as naive about it as the students you are protecting..

    Maybe hand "straining" to remove the 2 materials is a better idea as far as safety and simplicity is concerned.. As is..while it is a fairly simple concept.... making a functional prototype is not a 1 day job..
    I mean its a math class..... Who builds functional electro-mechanical devices in math class.. Thats what science class is for :) and even then the scope of the project you are detailing is quite a bit more than any science class I've ever had..
    What ever happened to popsicle bridges and co2 drag cars ;)

    Or what specifically is your question? how to make a simple motor move?
    or how to mechanically couple a motor to a rotating drum or what? Its quite an involved post you could have here..
     
  3. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi Kelly.
    Have you considered leaving the water in the cylinder.?

    Have a circular perforated disc that fastened at its centre to the end of a long rod that will reach to the bottom the cylinder, by pulling up the rod after the solids have settled you will raise the heavy objects on the face of the perforated disc, leaving the water in place.!

    I would also solve the problem of the lighter solids by adding more water to the cylinder so that they float to the top of the cylinder.

    IMO I think a 'purely' mechanical solution would be more elegant.:)

    E.

    EDIT:
    Just seen this statement in your post #2!
     
  4. KellyGates

    Thread Starter New Member

    Mar 4, 2014
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    It's actually for a science project (having nothing to do with my class), but the science teachers need help. So, I'm trying to teach myself to help these kids. I know electricity and water is normally not a good mix, but we can't come up with another way to do it. The process must be completely automated - we can't physically touch it. So, I guess my question is more about the pairing of the motor and the rotating drum. How would I start and what pieces do I need to purchase. I plan to figure this out and wire it up several times (and figure all this out) before I ever talk to the kids. I have about a month to figure out how to do it...
     
    Last edited: Mar 8, 2014
  5. KellyGates

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    Mar 4, 2014
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    This could definitely work, but I would need to figure out a way to completely automatize it, so the solids end up in separate pre-marked containers without the kids touching it...
     
  6. BillB3857

    Senior Member

    Feb 28, 2009
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  7. wayneh

    Expert

    Sep 9, 2010
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    Industrial centrifuges of all sorts are used for density-based separations. The simplest are dorrclones, which have no moving parts. What you are describing reminds me of a basket centrifuge, where solids collect on the walls of the spinning chamber (the bowl), fluid passes thru them and slings outward to drain to the bottom. If the bowl fills, the input mixture overflows to the drain.
     
  8. KellyGates

    Thread Starter New Member

    Mar 4, 2014
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    Okay, I'm familiar with the centrifuge idea. I've always thought of them separating a liquid from a solid. How might a basket centrifuge separate two solids?
     
  9. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Does it need to perform the task over without any intervention over and over or can it be setup..then performs the task once.. then can be setup again (like a Rube Goldberg machine)?

    ericgibbs has given the best direction so far IMO.. Float out the floaters and then strain out the sinkers while keeping the cylinder wet.


    also
    is microprocessor programming out of the question for this project (arduino maybe)?
    your current idea requires stopping/starting/timed,etc.. motor movements which will require some "programming" to perform.
     
  10. wayneh

    Expert

    Sep 9, 2010
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    OK, I misread your original post but went back and read it again. Forget what I said about centrifuges.

    Instead of agitating the bed inside the column (which I assume you need to allow the floaters to rise through the sinkers?), consider a fluidized bed. You can add the same energy to the bed as you would with an impeller, by instead using a water pump to give a good upflow. At some flow rate, the sinkers will move enough to free the floaters. These can then exit the top and be caught on a screen as the water falls back into the pump's intake reservoir. Using a denser liquid and/or more viscous fluid (salt water, sugar syrup) would reduce the required flow rate.

    For this process to run batch wise, you'd load the column, turn on the pump for a fixed time and flow rate to collect all the floaters, then dump the sinkers. At larger scale you'd ramp the flow rate gradually, but I don't think that would be required at bench scale.
     
  11. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Why mix the water and the electricity? I have a device in my kitchen that can accomplish the spinning task with near perfect safety, just keep your hands out of it:

    [​IMG]
     
  12. KellyGates

    Thread Starter New Member

    Mar 4, 2014
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    It only has to run the task once and then can be setup again... yep.. like a Rube Goldberg. Keeping the cylinder wet is fine. My idea was just to plug the bottom and release the plug at some point, letting the water out into a cup. It's the whole figuring out how to float out and strain out in an automated way that trips me up. The kids can't actually interfere with the machine. All electric and electronic components except computers and integrated circuits are permitted. You can have an unlimited number of motors.

    I've actually just ordered an arduino for beginners kit so I can learn (hopefully quickly) about them. I figured that was the route I was headed down.
     
  13. KellyGates

    Thread Starter New Member

    Mar 4, 2014
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    I'm not actually convinced that the column needs to be agitated. The solids will be dropped into the container. One is made of heavy-ish glass and the other of light plastic. They should separate quite easily, I should think. I get the idea you're going for (I think), but I'm no longer convinced we need a pump (I was just trying to figure out a way to get the water out). All the kids have to do is separate the two solids (preferably without the water) into two separate cups/containers. The separation part is the point of this inquiry. I'm fairly sure that one will float and one will sink upon hitting the water... the problem is the next part... the separation.
     
    Last edited: Mar 4, 2014
  14. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    It's very easy.

    Just put the mix in a tall container, then stick a hose in it so the hose adds water near the bottom of the container.

    As you add water all the added water overflows out the top of the container, taking all the floaties with it. All the heavies will stay in the bottom of the container.

    No mechanical devices are needed, just a container and a hose. :)
     
  15. wayneh

    Expert

    Sep 9, 2010
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    Yes, that's the fluidized bed idea. I've used it myself at industrial scale. Sounds like the OP thinks the materials will separate without any energy added for agitation (although maybe a shaker/tapper would help?).

    The project challenge seems to be mostly how to automate the collection of the two fractions once they are separated.

    I don't understand the "specifications". I mean, if the floaters have gone out the top and collected on a screen (like a kitchen sieve), leaving the sinkers in the column, what more needs to be done? Dump the column? Dump the sieve? In short, what is the final state after the machine completes its cycle? What is the starting state - can it include the water loaded into the column, or does that have to be automated?
     
    djsfantasi likes this.
  16. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Let the floaters overflow into a pan at the base of the cylinder which can be cleared into your collection container with a wiper. Or put a channel around the cylinder with a spout to deliver the floaters into their separation container.

    The microcontroller can be used to run the sequence. Start water pump. Time or sense when the cylinder is filled. Then potentially speed up the pump to loosen the floaters. Time or sense when the floaters have separated. Pump the water out.

    If separate containers are needed, make the separation chambers with hinged bottoms, so that once separation is completed, the doors can open, and the separated materials can fall into their own collection chambers.
     
  17. sirch2

    Well-Known Member

    Jan 21, 2013
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    If I understand the requirement correctly the kids have come up with the design and you are not asking for advice on how to separate the materials, this kids have done that. You want to implement their idea. And again if I understand correctly the rotating part is like a valve (vane) in the middle of the cylinder, you set the vane vertically pour the mixed materials into the water, the floats float and the sinks sink. You then close the vane and drop the contents, taking out the sinks and leaving the floats. you then open the valve dropping the floats?

    What size do you envisage the cylinder being? What size are the particles?.
     
  18. KellyGates

    Thread Starter New Member

    Mar 4, 2014
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    That makes sense and I think is what someone else was saying to do. Two concerns. (1) How do we not make a mess... it's supposed to have a small footprint and be neat (I guess you could catch everything in a pan, but that leads me to the next question) (2) Both groups of objects have to be separated into individually marked plastic cups (think styrofoam or so size). (3) How do the kids trigger the water to start or at least keep it going? We can't just attach a hose. This has to stand alone and be portable... some sort of pump?
     
  19. KellyGates

    Thread Starter New Member

    Mar 4, 2014
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    Sorry. I guess I need to be a bit more clear. The objects have to end up in individually marked cups (about styrofoam coffee cup size). So, if the kids go with the fluid bed idea (which, granted seems a lot easier on the gray matter), how do they get the glass objects (10 marbles) and the plastic stuff (10 golf tees) separated into cups?
     
  20. KellyGates

    Thread Starter New Member

    Mar 4, 2014
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    This sounds exactly like what we need to happen. Now, if I was just smarter... the only thing is that the floaters are golf tees, so they aren't going to cooperate that well with the idea of a channel, I think. (They have always gotten stuck when the kids try chutes and things)...

    So, the kids would need

    1) a wiper (umm... are these kind of things available for purchase?)
    2) microcontroller
    3) water pump


    Only problem is that separation chambers can't be hinged. Basically it has to be a cup.
     
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