Re: Dragforce In Pipeflow With Large Particles
Dear Mr Ringenhall,
A particle in a flowing medium is propelled by the transfer of impulse from the flowing medium to that particle.
This is a good approximation in case the particle size is small compared to the pipe diameter.
(pneumatic conveying of powders)
As the particle size approaches the pipe diameter, an additional pressure drop over the particle is created by the air flow resistance between the particle and the pipe wall.
When this gap becomes zero, the gas resistance becomes infinite.(the particle has become a piston).
Looking at the physical phenomena in this way opens the possibility of calculating.
To answer your last questin, I would say “you are right”
Success
teus ■
Teus
Dragforce in pipeflow with large particles
Hi,
normal theorys with pneumatic conveying discribes the transport velocity to be driven by the dragforce that comes from among other things the "slipvelocity" between the particle and airstream. But when you start to have larger particles that takes up a larger portion of the cross section area is this the only thing that drives the transport?
At some point the pressure difference above the particle must starts to influence the transportation but I have not found any references in this field. My particles is domestic waste, hence the particles are waste bags that could be said to be spheres with a diameter of about 300 mm and they are transported in pipes of 400 to 600 mm diameter pipe depending on other things. I'm simplifying a great deal just for the discussion...
Given the same speed of the air stream my oppinion that I don't have to much to back-up with at the moment is that the velocity of the particle will be higher in the 400 mm pipe than in the 600 mm pipe since the pressure difference over the particle is bigger in the case with the 400 mm pipe and hence gives extra force in the direction of the flow. Can anyone give me references or proofs that I'm right or wrong in this?
Best Regards ■