Question 7.P.17: The flow in a pipe of 100 mm dia with Reynolds number value ......
The flow in a pipe of 100 mm dia with Reynolds number value of 10^{5} is found to have a friction factor f = 0.032. Determine the thickness of laminar sublayer. Also indicate whether the pipe is hyraulicaly smooth or not if the roughness height is 0.4 mm.
Step-by-Step
Ref. section 7.5.
\delta_{l}=32.8\ v/u_{m}\ \sqrt{f}\ ,R e=u_{m}\,D/v=10^{5}
∴ v/u_{m}=D/10^{5},{\mathrm{substituting~for~}}v/u_{m} \\ ∴ \delta_{l}=(32.8\times D)/(10^{5}\times\sqrt{f}~)=32.8\times0.1/10^{5}~\sqrt{0.032}=1.83\times10^{-4}\,{\mathrm{m}}=0.183\,{\mathrm{mm}} \\ ε = 0.4\ \mathrm{mm} 0.3 ε = 0.12\ \mathrm{mm}, 6ε = 1.098\ \mathrm{mm}
The sublayer thickness is larger than 0.3ε but less than 6ε.
The pipe cannot be classified definitely as smooth or rough.
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