I would like to ask fellow sailors some questions regarding the formula for the friction loss in straight pipes
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According to Fanning’s formula given in the first volume of the third edition of Chemical Engineering Principles, hf = λ*L*u²/2d; the units of this formula’s result are J/Kg. By dividing this value by g, we obtain the head loss Hf = λ*L*u²/2dg, whose units are m. However, according to the Industrial Metal Piping Design Code, page 63, the frictional loss in a circular straight pipe is given by ΔPf = 10⁻⁵λ*L*u²*ρ/2dg, and the units of this formula are MPa. I’m not sure how this ΔPf value is calculated. If we use the formula ΔPf = ρ*g*Hf, then there’s an extra factor of g in this formula. I hope those who understand this can explain it to me. Another point is regarding the friction resistance coefficient λ in turbulent flow – does this need to be found from a chart? It is better to use other formulas for calculation. According to the principles of chemical engineering, flow enters the turbulent regime when Re>4000; when the Reynolds number is high enough, the friction coefficient λ no longer changes with the Reynolds number. But just how high does this \"high enough\" value actually need to be? Thank you all
Is there no one to help me solve this problem?
Go to the process section to take a look @*lihuagong @dlutyj
The first one should be Wf=λ*L*u2/2d, with the unit being J/Kg. The second one is Hf=Wf/g, where g has the unit of N/Kg. Since J (work) = N (force) * m (distance), Hf’s unit is m. The third one is ΔPf=ρ*Wf, with ρ having the unit of Kg/m3; therefore, ΔPf’s unit is J/m3. And since J=N*m, J/m3 can be converted to N/m2, which is Pa. There’s no problem at all :)
Another point is regarding the friction resistance coefficient λ in turbulent flow – does this need to be found from a chart? It is better to use other formulas for calculation. According to the principles of chemical engineering, flow enters the turbulent regime when Re>4000; when the Reynolds number is high enough, the friction coefficient λ no longer changes with the Reynolds number. But just how high does this \"high enough\" value actually need to be? Answer: Please check the Moody chart; once you understand it, your question will be resolved.
According to the principles of chemical engineering, flow enters the turbulent regime when Re>4000. When the Reynolds number is high enough, the friction coefficient λ no longer changes with the value of Re. But just how high does this sufficient value need to be?
The critical Re value varies with different relative roughness levels, and it is necessary to consult a Moody chart. Therefore, the critical Re is related to the effective roughness of the pipe and its diameter.
Different roughness levels: smooth and rough, with a significant difference
Formula calculation is also an option, but it’s not as intuitive as the Moody diagram.