The exponent 0.8 in the h-Re relationship is characteristic of which flow regime in pipes?

The exponent 0.8 in the h-Re relationship is characteristic of which flow regime in pipes?

• A. Turbulent flow.
• B. Laminar flow.
• C. Transitional flow.
• D. Stagnant flow.

Answer: (A)

The main idea is how head loss due to friction in a pipe scales with Reynolds number and what that tells you about the flow regime. In laminar flow, viscous forces dominate, and the friction factor decreases with Re in such a way that head loss grows roughly linearly with Re (a near-linear relationship). In turbulent flow, inertia takes over and the friction factor drops with Re, so head loss increases with Re but at a slower, sublinear rate. An empirical h-Re relation with an exponent around 0.8 reflects that sublinear growth, which is typical of turbulent pipe flow where eddies and mixing reduce the rate at which added Reynolds number translates into additional friction losses. Transitional flow would not have a consistent, fixed exponent and can be unstable, while stagnant flow has essentially no flow and does not follow a meaningful h versus Re trend. Therefore, an exponent of 0.8 is characteristic of turbulent flow.

The main idea is how head loss due to friction in a pipe scales with Reynolds number and what that tells you about the flow regime. In laminar flow, viscous forces dominate, and the friction factor decreases with Re in such a way that head loss grows roughly linearly with Re (a near-linear relationship). In turbulent flow, inertia takes over and the friction factor drops with Re, so head loss increases with Re but at a slower, sublinear rate. An empirical h-Re relation with an exponent around 0.8 reflects that sublinear growth, which is typical of turbulent pipe flow where eddies and mixing reduce the rate at which added Reynolds number translates into additional friction losses. Transitional flow would not have a consistent, fixed exponent and can be unstable, while stagnant flow has essentially no flow and does not follow a meaningful h versus Re trend. Therefore, an exponent of 0.8 is characteristic of turbulent flow.