For a hydraulically long pipe run, which head-loss components are commonly neglected in comparison to the dominant losses?

Introduction / Context:
In extended pipeline systems, designers must decide which loss terms significantly impact total head requirements. Over long distances, some localized losses are negligible when compared to frictional head loss distributed along the pipe length.

Given Data / Assumptions:

• Steady, incompressible flow in a long, prismatic pipe.
• Minor losses (entrance, exit, fittings) are small relative to major (friction) losses over long lengths.
• Fully rough or transitional friction factors may apply, but the reasoning remains.

Concept / Approach:
Total head loss = friction loss (major) + sum of minor losses. For long pipelines, the Darcy–Weisbach friction term 4 f L/D * (V^2 / (2 g)) dominates. Entrance and outlet losses are finite and do not scale with L, so their relative contribution diminishes as L increases.

Step-by-Step Solution:
Estimate friction head: h_f ≈ 4 f (L/D) (V^2 / (2 g)).Entrance and exit losses: h_e = K_e V^2/(2 g), h_o = K_o V^2/(2 g), with K’s of order unity.For L/D large, h_f ≫ h_e + h_o → neglect entrance and exit in preliminary sizing.

Verification / Alternative check:
Numerical example shows that for L/D in the thousands, minor-loss contributions are below a few percent of total head, justifying their omission in first-pass design.

Why Other Options Are Wrong:
Entrance only / exit only: both are minor, and both are typically neglected together.Friction loss: cannot be ignored; it is dominant in long lines.“Minor losses in fittings”: may or may not be negligible depending on numerous fittings; the safe generalization is about entrance and exit specifically.

Common Pitfalls:

• Neglecting significant valve and fitting losses in complex networks.
• Using this simplification for short pipes where minor losses can be comparable to friction.

Final Answer:
Both entrance and exit losses