Which type of difference is the primary driver of flow in a closed tube?

Which type of difference is the primary driver of flow in a closed tube?

• A. Pressure difference
• B. Temperature difference
• C. Viscosity difference
• D. Density difference

Answer: (A)

Flow in a closed tube is driven primarily by the pressure difference between the tube’s ends. This pressure difference creates a gradient that pushes the fluid from high pressure toward low pressure, generating the net motion along the tube. The size of the flow depends on that pressure difference and on resisting factors like viscosity and the tube’s geometry (as shown in the laminar-flow relation Q ∝ ΔP/(μL) with the radius amplifying flow). Temperature differences can influence viscosity and density, which in turn affect how easily the fluid flows for a given ΔP, but they don’t set the driving force itself. Density differences would drive flow mainly in natural convection scenarios where buoyancy matters, not in the ordinary closed-tube flow driven by a pressure source.

Flow in a closed tube is driven primarily by the pressure difference between the tube’s ends. This pressure difference creates a gradient that pushes the fluid from high pressure toward low pressure, generating the net motion along the tube. The size of the flow depends on that pressure difference and on resisting factors like viscosity and the tube’s geometry (as shown in the laminar-flow relation Q ∝ ΔP/(μL) with the radius amplifying flow). Temperature differences can influence viscosity and density, which in turn affect how easily the fluid flows for a given ΔP, but they don’t set the driving force itself. Density differences would drive flow mainly in natural convection scenarios where buoyancy matters, not in the ordinary closed-tube flow driven by a pressure source.