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Small Turbine

  1. Dec 10, 2009 #1
    hey all,

    for a science league competition, my team-mates and I are tasked with building a turbine that will draw as much power from a box-fan as possible. Every team has been given an identical motor and the rules specify that we can't modify the motor at all. I've asked around and it seems like what I should be doing is making my fans as big and light as possible to maximize the amount of force they absorb from the wind. Would anyone be so kind as weigh in?
     
  2. jcsd
  3. Dec 11, 2009 #2
    I would say do some research on real life electrical generating wind turbines. They're exactly what you're looking for, and the best solution to the problem has already been found.
     
  4. Dec 11, 2009 #3

    minger

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    What about adding a diffuser row after the fan, and then dumping into a combustor?

    Seriously though, I don't think wind turbine are very effiicient, I think you can do MUCH better by approaching the turbine as you would a turbine stage in a gas turbine engine.
     
  5. Dec 11, 2009 #4

    FredGarvin

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    I don't know. You won't have anything for a delta P. A box fan doesn't really give you anything to work with other than velocity. This would be more like an impulse turbine or a Pelton wheel IMO. Perhaps your idea of a diffuser could be switched around and put a nozzle on the outlet of the fan. I have no idea how much the box fan would not like it, but if you could put a plenum and then a nozzle that reduces down to try to get your velocity way up and then point that at a Pelton wheel...
     
  6. Dec 11, 2009 #5

    minger

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    True box fans aren't going to give you much of; you're idea's not bad though. Velocitie are low so losses are too. You're in effect then reducing the area where you're getting low efficiency. You would at least get points for creativity.
     
  7. Dec 12, 2009 #6

    Danger

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    I ashamedly admit that I had to look up 'Pelton wheel' to find out if we were on the same page. Almost, because my first thought was what I know as a 'pinwheel'. That's one of those things that you get at a fair when you're a kid, with usually 4 'blades'. I guess that it's the kindergarten version of a Pelton wheel. Anyhow, my first thought toward this matter is that a few really fat blades with moderate pitch would be more appropriate in this airflow situation than what one would normally think of as a 'turbine', such as the working end of a J-34. Once again, though, my lack of education leaves me wondering...
     
  8. Dec 14, 2009 #7
    the styrofoam kids sail planes may yield up a couple potential blades, and they'd be pretty matched. being as velocity is so low, and flow is very controlled, wouldn't the vertical windmill style be a better fit? have the fan blow on the one side, and then the reverse losses would be decreased because of no wind on them?

    dr
     
  9. Dec 14, 2009 #8

    minger

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    Have you done any research into Pelton wheels as Fred suggested? They have used those in hydroelectricity, which operate typically at significantly higher efficiencies than wind power.

    If you check out:
    http://en.wikipedia.org/wiki/Water_turbine#Design_and_application

    There are some other low-head designs such as Kaplan Turbines
     
  10. Dec 14, 2009 #9

    FredGarvin

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    It would appear that this was a post and run.
     
  11. Dec 14, 2009 #10

    minger

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    whoops, I actually thought that dr.dodge was the OP. Oh well...
     
  12. Dec 15, 2009 #11
    I'm not sure what a box fan is, but guess that it's a fan with some kind of shroud round the fan. The first thing to do is get the fan working as hard as possible, hokk an ammeter onto your motor feed and see if different diffusers make the fan work harder, when you have the max power coming off the fan you can start to design the turbine for the air speed that you are getting at the diffuser outlet.
     
  13. Dec 19, 2009 #12
    well I need to look up about half of the stuff you guys are saying, especially a pelton wheel, but thanks for all the help
     
  14. Dec 19, 2009 #13
    and sorry for taking so long to reply, the college admissions process has eaten up all of my time lately
     
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