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Thread: How a propeller blade is resisted by various viscosity?

  1. #1

    How a propeller blade is resisted by various viscosity?

    I'm building propeller blades to blend various solutions.
    But I'm stuck: is there a formula to determine the resistance a specific viscosity will provide against a surface area?


    Meaning, if the liquid has a visocosity of water, or very near to it, the force required to "mix" it will be differant that something that has a viscosity of, oh, say, suntan lotion.


    Of course the blade profile will affect the resistance, but, if the blade profile is static, how do I figure out how much power is needed to turn the propeller at a specific rpm for each viscosity?

    I'm pretty much at a loss on this one....

  2. #2
    Lead Engineer Cake of Doom's Avatar
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    Is this so that in the act of "mixing", you don't get the drill in a paint can effect? How accurate do you need it be? So many variables at play with this one.

    P.S.

    I hated fluid mechanics and I hope you will too .

    Edit to elaborate:

    The faster the object moves, the more negligible the viscosity drag becomes and gives way to fluid density for an inertial equation.
    Last edited by Cake of Doom; 11-01-2017 at 07:13 AM.

  3. #3
    Quote Originally Posted by Cake of Doom View Post
    Is this so that in the act of "mixing", you don't get the drill in a paint can effect? How accurate do you need it be? So many variables at play with this one.

    P.S.

    I hated fluid mechanics and I hope you will too .

    Edit to elaborate:

    The faster the object moves, the more negligible the viscosity drag becomes and gives way to fluid density for an inertial equation.
    The most important effect is that the substance be thoroughly mixed.
    The "substance" is unknown at this point, hence the question.

    I'm basically pondering how strong a propeller (impeller?) blade needs to be for various substances.

    So it seems like viscosity vs surface area would be at play.
    I didn't realize that the faster a blade moves through a liquid, the less viscosity plays a factor.

    That makes sense from experience.
    It seems like I'm going to need some professional help on this one.
    What is it that I'm looking for? A guy with 'fluid dynamics' experience?

  4. #4
    Lead Engineer Cake of Doom's Avatar
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    Yeah this might be a bit easier for someone with the modeling tools, so they play about with the variables. When I get to the office tomorrow, I can post the graph for the Reynolds numbers for various viscosity and some basic equations. It may not be much help but it can get you in the basic ball park if that’s any good to you?

  5. #5
    Yes, that will at least help me understand the discussion.

  6. #6
    Lead Engineer Cake of Doom's Avatar
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    Upon further review... I think it's going to more useful to you to find a specialist straight off the bat. Maybe a pipeline of aeronautical engineer. I've looked at the equations for laminar, transitional and turbulent flow and it's not good. I haven't the experience to reduce these down to a simple form that would allow you to tweak the variables and going through the lot is well, literally, a books worth. Sorry if I got your hopes up.

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    Propeller power is governed roughly by the cube of the diameter. I would be tempted to make some and trim the diameter as needed.

  8. #8
    Lead Engineer Cake of Doom's Avatar
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    To clarify: does liquids of varying viscosity mean you want to smash an emulsion together or is for another application like say, mixing a liquid with a gas? I've put a link below to existing configurations and the math behind them. It's actually quite an interesting read too.

    Link to PDF for existing mixers/agitators. Warning! May contain traces of math! -> MixingandAgitation93851_10.pdf

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