What factor determines if the flow is turbulent or laminar?

• A. Pressure gradient
• B. Reynold's Number
• C. Pipes' roughness
• D. Flow velocity

Answer: (B)

The determining factor for whether the flow is turbulent or laminar is the Reynolds Number. The Reynolds Number is a dimensionless quantity used in fluid mechanics to predict flow patterns in different fluid flow situations. It takes into account the fluid’s density, velocity, viscosity, and characteristic length (such as diameter of a pipe) to quantify the flow regime.

In general, a low Reynolds Number (typically less than 2000) indicates laminar flow, where fluid moves in parallel layers with minimal mixing and disruption between them. Conversely, a high Reynolds Number (typically greater than 4000) indicates turbulent flow, characterized by chaotic changes in pressure and flow velocity that lead to increased mixing and swirling.

While factors such as pressure gradient, pipe roughness, and flow velocity can influence flow conditions, it is ultimately the Reynolds Number that provides a clear threshold between laminar and turbulent flow.