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Kinetic energy of fluid + collision

  1. Nov 27, 2015 #1
    Hello,

    When a fluid is flowing, it has of course a kinetic energy and thus we can define kinetic power equal to ρAv v is the velocity and A is the surface of a solid for example. I have a question (maybe it is a strange one) : When fluid collides with a solid, do all the molecules collide with the solid or some of them or we cannot know?

    Thanks
     
  2. jcsd
  3. Nov 27, 2015 #2

    Vanadium 50

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    When you put a penny in a river, does ever molecule of water collide with the penny?
     
  4. Nov 27, 2015 #3
    I am talking about the quantity ρAv
     
  5. Nov 28, 2015 #4

    Vanadium 50

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    Which is not a volume.
     
  6. Nov 28, 2015 #5
    how it is the mass of the volume Av
     
  7. Nov 28, 2015 #6

    Vanadium 50

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    I don't understand that. It is not a sentence, and Av is neither a mass nor a volume.
     
  8. Nov 28, 2015 #7
    Velocity multiply by surface you will get m3/s so it is a volumetric flow rate. If you multiply by ρ(rho) we will get mass flow rate.
     
  9. Nov 28, 2015 #8

    Vanadium 50

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    We're not getting anywhere. Why not pose your question again, as quantitatively as you can: using expressions for as many terms as you want to compare as possible. Keep in mind that quantities that you want to compare need to have the same dimensions.
     
  10. Nov 28, 2015 #9
    When we say that a fluid has a kinetic energy equal to 1/2 M V2 colliding with a solid, usually we talk about the power of the fluid that is equal to 1/2ρAV3 where V is the velocity of the fluid and A is the surface of the solid. My question is: in the quantity ρAV (mass flow rate), all the molecules in this mass flow is colliding with the solid or it is just like a collision between two solids?
     
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