Which statement about flow in a vessel is true?

Which statement about flow in a vessel is true?

• A. Fluid travels in parallel layers with minimal mixing.
• B. There is turbulent mixing between layers.
• C. Flow rate is independent of radius.
• D. Laminar flow only occurs in gases.

Answer: (A)

In laminar flow through a vessel, the fluid moves in distinct, parallel layers with minimal mixing between them. Each layer slides smoothly past the one next to it, creating a smooth velocity gradient from the center toward the wall without interlayer chaos. This is exactly what the statement describing flow as parallel layers with little mixing is getting at, so it’s the correct description of typical laminar flow in a vessel. If there were turbulent mixing between layers, the motion would be chaotic and not laminar, which is why the alternative about turbulent mixing doesn’t fit laminar flow. Flow rate is not independent of radius; in circular vessels, the flow rate grows steeply with radius (Poiseuille’s law shows a fourth-power dependence), so radius matters a lot. Finally, laminar flow is not limited to gases; liquids can exhibit laminar flow just as well, provided the conditions (viscosity, diameter, and speed) keep Reynolds number low.

In laminar flow through a vessel, the fluid moves in distinct, parallel layers with minimal mixing between them. Each layer slides smoothly past the one next to it, creating a smooth velocity gradient from the center toward the wall without interlayer chaos. This is exactly what the statement describing flow as parallel layers with little mixing is getting at, so it’s the correct description of typical laminar flow in a vessel.

If there were turbulent mixing between layers, the motion would be chaotic and not laminar, which is why the alternative about turbulent mixing doesn’t fit laminar flow. Flow rate is not independent of radius; in circular vessels, the flow rate grows steeply with radius (Poiseuille’s law shows a fourth-power dependence), so radius matters a lot. Finally, laminar flow is not limited to gases; liquids can exhibit laminar flow just as well, provided the conditions (viscosity, diameter, and speed) keep Reynolds number low.