In laminar flow, friction head loss is proportional to which?

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Study for the PE Environmental Qualitative Exam. Practice with flashcards and multiple choice questions, each question has hints and explanations. Get ready for your exam!

Multiple Choice

In laminar flow, friction head loss is proportional to which?

Explanation:
In laminar flow the viscous forces dominate, and the friction head loss follows a linear relationship with velocity. The Darcy–Weisbach form for head loss is h_f = f (L/D) (V^2 / 2g). In laminar flow, the friction factor is f = 64/Re, where Re = ρVD/μ. Substituting gives h_f = (64/Re) (L/D) (V^2 / 2g) = (64 μ / (ρ V D)) (L/D) (V^2 / 2g). The V^2 term is divided by V, leaving h_f ∝ V. So the head loss increases directly with velocity in laminar flow. In contrast, for turbulent flow the head loss is proportional to V^2.

In laminar flow the viscous forces dominate, and the friction head loss follows a linear relationship with velocity. The Darcy–Weisbach form for head loss is h_f = f (L/D) (V^2 / 2g). In laminar flow, the friction factor is f = 64/Re, where Re = ρVD/μ. Substituting gives h_f = (64/Re) (L/D) (V^2 / 2g) = (64 μ / (ρ V D)) (L/D) (V^2 / 2g). The V^2 term is divided by V, leaving h_f ∝ V. So the head loss increases directly with velocity in laminar flow. In contrast, for turbulent flow the head loss is proportional to V^2.

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