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Old   December 17, 2002, 02:39
Default developed turbulent flow ??
  #1
Gordon
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Hi I have a tube (nozzle) of 9.6 mm dia all along 200 mm in length.

At one edge the liquid is entering at 3 m/sec (velocity inlet, equal all along the radius).

Can I expect fully developed turbulent flow when it exit at the other end of the pipe (nozzle)??

Thanks in advance.

Gordon
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Old   December 17, 2002, 04:11
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Smith
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You neglect to say what 'liquid' you are using. assuming water at 20 degC, the Reynolds number for this flow field will be 28.7. Far too low for turbulent flow to develop. Viscous forces are dominating and will damp out any turbulent motion
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Old   December 17, 2002, 04:42
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Gordon
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I used d*v*ro/mu and got 28662, how did u calculate reynoulds number?

For case of water, with that 200 mm pipe (nozzle) is the flow developed ? I mean, should I expect any difference (specially turbulence parameters) at the exit if the pipe is 500mm?

Gordon
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Old   December 17, 2002, 09:24
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Smith
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Whoops! I used the wrong viscosity (kinematic instead of dynamic) OK, using the right numbers, yes you get Re=2.8e4 which puts you in the transitional zone for a a hydraulically smooth pipe.Which means you need to predict the point of transition - which is a bit tricky
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Old   December 17, 2002, 14:39
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wei
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The hydrodynamic entrance length has a relation of L/D=1.359*Re^0.25. Then L is about 170mm. So, after that length, the turbulent flow is fully developed.
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Old   December 17, 2002, 16:32
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Gordon
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Hi Wei, Is that applicable for a capillary flow as well?

Gordon
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Old   December 18, 2002, 09:23
Default Re: developed turbulent flow ??
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chidu
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i guess it would not be applicable for capillary flows! but 9.6 mm diameter would still be in a low Knudsen number regime by far.

Chidu...
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