The Swamee-Jain formula is used to estimate the Darcy friction factor directly for turbulent flow in pipes.

• A. Only for laminar flow
• B. False
• C. Only for smooth pipes
• D. True

Answer: (D)

In pipe flow, the friction factor (Darcy) for turbulent conditions depends on both the Reynolds number and the pipe’s relative roughness. The Swamee-Jain formula gives a direct, explicit way to estimate that friction factor from Re and the relative roughness, so you don’t have to solve an implicit equation. The common form is f = 0.25 / [log10( (ε/D)/3.7 + 5.74 / Re^0.9 )]^2, valid for fully turbulent flow (typically Re above a few thousand) and a range of roughness values. Because it includes roughness, it’s not limited to smooth pipes; when roughness is zero, it still produces the smooth-pipe friction factor as a function of Re. It’s also not used for laminar flow, where f = 64/Re applies. So the statement is true: the Swamee-Jain formula estimates the Darcy friction factor directly for turbulent flow in pipes.