Would water left to rest produce a laminar stream?

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Would water left to rest produce a laminar stream?

Post  ericsundbergva on Thu Jun 23, 2016 3:34 am

Has anyone tried using a 4 inch or so pvc pipe with NO straws but with a good laminar nozzle, Let the water rest than applying pressure is a uniform manner, perhaps with air pressure?

Or is the flow through the straws really needed.
Thanks

Erc (newbie)

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WOULD WATER LEFT TO REST PRODUCE A LAMINAR STREAM?

Post  tangnla on Wed Jul 06, 2016 3:04 pm

Hi Eric,

I've tried a 6 inch tube, 0,5 meter in length without straws, just to see what would happen. The result? Not laminar. And the simple answer is that the  Reynolds number is to high. The Reynolds number has to be below 2300 to achieve laminar flow, that's the reason for the drinking straws.

I then put 1000 drinking straws with a diameter of 4,5 mm and 200 mm in  length. When you calculate you will get a Reynolds number at 90 @20 l/min. In the large tube you get a Reynolds number at 2907 which will lead you into turbulent flow.

I also injected ink to see what happened, and there were lots of turbulences. Se picture below. There's actually a video but I don't know if it's possible to post large videos in the forum.

The bottom plate is drilled to act as a distributor. The inlet is not axial as it looks in the picture. Another picture shows how it's done.







Lars

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