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Old Feb 16th 2017, 06:34 AM   #1
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Question Turbulent flow in duct calculations

Dear All,

I am new to this forum, so hello and thanks in advance for any advice I will get now and in the future.

Regarding this post, I am trying to figure out the flow rate for water moving between two vertical glass parallel panels, 3 m long 2 m high, forming essentially a narrow duct of 3 cm.

So I have water flowing in this narrow channel, with a driving pressure of 1962 Pa (or 883 if we consider the presence of gas), and I know the dimensions of the duct.

I did an iterative excel where I use the Darcy–Weisbach equatiton to calculate velocity and flow rates, assuming an initial flow rate. I calculated this initial flow rate using the maximum velocity obtained from CFD calculations, 3 m/s, and from there I obtained

1) a value for Friction factor (assuming Completely turbulent flow and considering glass roughness)
2) Reynolds number

and using this Re, I re-calculated the Frictional number several times for the transition region of the flow. From here finally I obtained a new velocity value, way smaller then the assumed one, 0.1 m/s and finally a Flow rate depending on my cross-sectional area. However, the results seems still to high for a geometry like this: 4500 l/m.

Because this is not my field and I need these calculation for deciding pumping requirements, I am wondering: Is this the correct way to calculate the turbulent flow without having any initial information if not the liquid properties and geometry dimension? Am I missing something or not considering something? According to a quick 2D simulation with Comsol the flow rate is even higher, but again, for a flow like this in a narrow duct, it seems way too high.

Any help or advice is greatly appreciated.
Thank you very much,

All the best

A.

Last edited by TXVIII; Feb 16th 2017 at 06:51 AM.
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