Question 1

What is the difference between Darcy-Weisbach and Hazen-Williams?

Accepted Answer

Darcy-Weisbach is a physics-based equation that works for any fluid (water, oil, glycol) in any flow regime. It uses surface roughness and requires solving for the friction factor. Hazen-Williams is an empirical formula calibrated specifically for water in turbulent flow, using a single C factor per material. Use Darcy-Weisbach for accuracy or non-water fluids; Hazen-Williams for quick water system estimates.

Question 2

How do pipe fittings affect friction loss?

Accepted Answer

Fittings like elbows, tees, and valves create additional turbulence and friction. Each fitting is equivalent to a certain length of straight pipe (the L/D ratio). For example, a globe valve adds the equivalent of 340 pipe diameters. Ignoring fittings can undersize pumps by 20–40% in typical systems.

Question 3

Why does pipe diameter matter so much for friction loss?

Accepted Answer

Friction loss is inversely proportional to roughly the 5th power of diameter. Doubling the pipe diameter reduces friction loss by about 97%. Conversely, halving the diameter increases it roughly 32 times. This extreme sensitivity is why proper pipe sizing is critical for system efficiency.

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