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Total pressure drop in laminar channel flow (calculation of friction factor) |
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October 24, 2021, 13:16 |
Total pressure drop in laminar channel flow (calculation of friction factor)
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#1 |
New Member
HOU Xiao
Join Date: Oct 2021
Location: Nantes, France
Posts: 1
Rep Power: 0 |
Hello everyone,
I'm calculating the total pressure drop at Re = 2000, for water at 300K in a pip D = 0.1 m, L = 2 m. And this is a verification for the other studies. The problem is, the theoretical result for friction factor is around f = 64/Re = 0.032, but the result is much higher (f = 0.0729). Could you help me to verify my settings as follows? ------------------------------------------------------------ Re = 2000, density: 998.2 kg/m^3, viscosity: 0.001003 kg/(m s) As a result: hydraulic-diameter: 0.1 m (for pip D = 0.1 m) inlet-velocity: 0.0201 m/s sandgrain roughness height = 0 ------------------------------------------------------------ Results: Area-Weighted Average Total Pressure: inlet: 0.49894214 Pa outlet: 0.20497435 Pa friction-factor: f = 0.0729 >> 0.032 ------------------------------------------------------------ Did I make a mistake of common sence or there are something special to be noticed? |
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October 24, 2021, 18:48 |
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#2 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,750
Rep Power: 66 |
64/Re is for fully developed flow.
Are you using streamwise periodic BC's or is this with a velocity inlet and outlet type calculation? You might need to take into account developing effects. |
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October 2, 2023, 02:27 |
the result is not matching with theoretical calculation
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#3 |
New Member
Sumeet kotak
Join Date: Jun 2015
Posts: 13
Rep Power: 11 |
I am facing the same issue.
Simple fluid Flow problem Problem Description: Pipe diameter: 0.0478 m density: 998 kg/m^3 Velocity: 0.036 m/s theoretical calculation: Re: 1500 Friction factor f=64/Re delta P= 0.57 Pa Fluent Analysis: Inlet BC: Velocity inlet outlet BC: Pressure outlet 0 Pa (atmospheric condition) Model: laminar Result: Pressure at inlet: 1.23 Pa delta P = pressure inlet - pressure outlet = 1.23-0 = 1.23 Pa which is 115% higher than theoretical value. Need help Thanks in advance |
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October 2, 2023, 02:57 |
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#4 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,750
Rep Power: 66 |
A velocity inlet is not a fully developed flow. The theoretical value for this case is NOT 64/Re. You can find in engineering handbooks the apparent friction factor for developing cases. Use the right formula! It should not match 64/Re. If anyone matches 64/Re for a developing flow then either they are a liar or they have messed up.
If you want to match 64/Re then use periodic BC's so that you do have a fully developed flow, or apply the fully developed profile at the inlet, or make the pipe super long so that entrance effects can be ignored. |
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October 5, 2023, 07:26 |
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#5 |
New Member
Sumeet kotak
Join Date: Jun 2015
Posts: 13
Rep Power: 11 |
Thanks for your response.
Can you help me how to apply fully developed profile as velocity inlet ? Thanks in advance |
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Tags |
fluent, friction factor, pip flow, pressure drop |
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