The major loss of energy in long pipes is primarily due to what?

• A. Gradual contraction or enlargement
• B. Sudden expansion and contraction
• C. Bend in the pipe
• D. Friction

Answer: (D)

In fluid dynamics, the major loss of energy in long pipes is primarily attributed to friction. When fluid flows through a pipe, it experiences resistance due to the internal roughness of the pipe walls as well as the viscosity of the fluid itself. This resistance leads to a significant amount of energy being dissipated as heat due to friction between the fluid layers and the pipe surface.

Friction loss is often quantified using the Darcy-Weisbach equation, which factors in the length and diameter of the pipe, the fluid's density, and the flow velocity along with a friction factor that accounts for the roughness of the pipe's inner surface. As the length of the pipe increases, the cumulative frictional losses become more pronounced, resulting in a substantial drop in pressure and energy as the fluid travels through the system.

While other factors like sudden expansions, contractions, or bends can contribute to localized energy losses (known as minor losses), these are generally less significant compared to the overall energy loss due to friction in long, straight runs of piping.