anyone seen this new dyson fan- and its potential for marine use?

Discussion in 'Propulsion' started by tugboat, Jun 24, 2012.

  1. tugboat

    tugboat Previous Member

    I saw this commercial the other day for a new dyson bladeless fan - epic!

    It kinda works like a jet- but forces a stream out of a foil --when i saw this
    i immediately saw the potential for more efficient prop systems...thoughts?
    i personnally think this is brilliant!
    think azimuthal drives(Z-drives)

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  2. CDK
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    CDK retired engineer

    That is the principle of an aspirator or venturi pump, used to expel corrosive or abrasive liquids. Divers also use it in their "vacuum cleaners" that expose object buried in the seabed.
    Of course there are still fan blades or pistons needed to obtain the flow of water or air, but at a more convenient location.
  3. daiquiri
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    daiquiri Engineering and Design

    I have thought about that fan right yesterday. The propulsive efficiency is probably not very high, because the work is done by a stream of high-speed flow coming out of nozzle on the inner front side of the ring. That flow induces (through viscosity or friction) a much bigger and slower flow of surrounding air (or water, should it be made for marine use). But high-speed flows are also flows with high dissipation of energy, hence the probable low efficiency.
    Besides, by the way it is made, the high-speed airflow coming out of nozzles washes the curved foil surface at it's full speed, thus creating a high friction drag. That's a feature you really want to avoid if you need an efficient propulsor.

    This video explains the working principle of that bladeless fan:
    BTW, I like the comment of the guy who wrote "I'm a metal fan, and I don't have blades too". :D

    The obvious (imho) advantages would be the simplicity of the construction, safety for swimmers and the absence of anything which could entangle into a floating rope. The disadvantages are, the said imho low propulsive efficiency (to be experimentally verified), and the necessity to keep the nozzle perfectly clean of marine growth, which is all but a simple task. We all know how aggressive and stubborn marine lifeforms can get when they decide to stick to an underwater surface. ;)
  4. PAR
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    PAR Yacht Designer/Builder

    It takes a bigger fan to push the same volume of air with the venturi setup Dyson uses. In other words, if you compare the volume of air coming off the outlet to a conventional fan of the same wattage, you get less volume with the venturi arrangement. You do gain some things, such as no exposed blades and less noise potential if the fan is well insulated. Having heard one in action it sounds like a vacuum cleaner (surprise) and is pretty loud, considering the air you get. I have a $15 box fan with 20" blades, that puts out more air at about the same noise level.

    According to Dyson, the hidden fan section draws in 42.2 CFM, which frankly isn't much and in all tests I've seen, that also didn't come with Dyson advertising on adjacent pages, the $300 Dyson didn't preform any better then a $20 Wal-Mart generic, conventional fan. The noise is absurd and several regular fans (curved, well shaped blades) proved less noisy.
  5. tugboat

    tugboat Previous Member

    Par- thats probably why they didnt have the sound of the fan going during the commercial:)...Yea--seems if what people here are saying is true it would be overly might be good for a small boat but the added complexity seems to negate any advantages...but it sure would be cool to have a bladeless type of system other than a jet drive...
  6. mydauphin
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    mydauphin Senior Member

    I thought about it for us in ports (windows for you landlubbers) in general. But I don't feel like buying a $300 fan to take it apart.
  7. DStaal
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    DStaal Junior Member

    I've seen them in stores, and never found them all that noisy - in fact, most of them that I've seen have been very quiet. Even Consumer Reports finds that it's a better fan - though not enough better to justify the cost.

    As a propulsion device though, I expect it'd have some drawbacks hidden someplace.
  8. Jeremy Harris
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    Jeremy Harris Senior Member

    They are grossly inefficient, and, IMHO, should carry a warning that they will consume far more energy for a given effect than a conventional fan.

    They are also a bit noisy, as the high pressure turbine in the base, that generates the high speed flow, isn't exactly quiet.

    Simple physics applies to any reaction propulsion system - accelerating a large volume of fluid to the lowest possible velocity above the vessels speed will ALWAYS be more efficient that accelerating a small volume of fluid to a velocity much greater than the vessels speed.
  9. upchurchmr
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    upchurchmr Senior Member

    You really need to see one in a store. Worked ok, but not great - not more air than an equal sized fan. $/cfm is really bad. Neat Gimick.
  10. Jeremy Harris
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    Jeremy Harris Senior Member

    I have seen a few, my former employer bought a few of them. They are probably about the same sound pressure level as an ordinary fan, but the higher frequency noise is definitely more annoying. They are also pretty inefficient, if you look at the power they consume for the amount of air they move.

    They're a neat gimmick, but not really a good way to waste energy moving air.
  11. tugboat

    tugboat Previous Member

    i wouldnt be surprised if someone takes this idea and makes it more efficient somehow - they keyword in the ad was- no buffering" ...if we could get a prop to not cavitate
    (which is what i assume is the equivelent to buffering in air ?) that would be something-of course the argument against that is- that truly effcient props dont cavitate anyway, because they run at low rpms and have large diameters....
  12. PAR
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    PAR Yacht Designer/Builder

    It still bashes the air to a froth, but then smooths it out as it also slows it down, shoving it up the tower, across the ramp and out the venturi, which does tend to even the flow a bit, but at considerable cost, when compared to the actual fan wattage. If you just remove the fan from the tower, place a well shaped blade on it, she will produce much more air, abet chopped up a bit.
  13. Jeremy Harris
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    Jeremy Harris Senior Member

    It's an old basic idea, one that's been around in one form or another for more than 100 years. It's deceptive, because the power-hungry high pressure turbine that produces the high velocity air stream that makes it work is hidden away in the base of the fan, where it can't be seen, making the thing appear to be a magic trick. You could make a marine version by using a high pressure pump to force water out through a ring of holes around a venturi, but the power absorbed by the high pressure pump would be greater than that absorbed by a conventional propeller by a big margin.

    As PAR rightly says, put a fan in that duct and you'll get far better efficiency.
  14. powerabout
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    powerabout Senior Member

    I have one at home and I just love the typical uneducated (modern educated I mean) person that cannot believe what they are seeing.
    Then tell them it has no moving

    Reminds me of the best one so far..
    21 year old Son of a ferry/shipyard owner asks me what is holding up the mast on his beach cat and the locals here complaining too many foreigners taking their jobs..

  15. Jeremy Harris
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    Jeremy Harris Senior Member

    I remember remarking to someone in the pub once that dry stone walls stayed up because of gravity. I sat back and watched a long, and mainly wholly wrong, argument take place at the bar...............
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