Kinetic energy of fluid + collision

[tonyjk]

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

 

[Vanadium 50]

When you put a penny in a river, does ever molecule of water collide with the penny?

 

[tonyjk]

When you put a penny in a river, does ever molecule of water collide with the penny?

I am talking about the quantity ρAv

 

[Vanadium 50]

I am talking about the quantity ρAv

Which is not a volume.

 

[tonyjk]

Which is not a volume.

how it is the mass of the volume Av

 

[Vanadium 50]

how it is the mass of the volume Av

I don't understand that. It is not a sentence, and Av is neither a mass nor a volume.

 

[tonyjk]

I don't understand that. It is not a sentence, and Av is neither a mass nor a volume.

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.

 

[Vanadium 50]

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.

 

[tonyjk]

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?