Fluid Dynamics & Flow Analysis Flashcards

In a piping system, the Moody friction factor for fully turbulent flow in a rough pipe depends primarily on:

Answer: Relative roughness only

At fully turbulent (wholly rough) flow, the friction factor becomes independent of Reynolds number and depends only on relative roughness (ε/D).

The hydraulic diameter for a rectangular duct with width W and height H is:

Answer: 4WH / (2(W + H))

Hydraulic diameter Dh = 4A/P = 4WH / (2(W+H)), used to apply circular-pipe correlations to non-circular cross sections.

Which phenomenon causes pressure oscillations when a valve is rapidly closed in a liquid piping system?

Answer: Water hammer

Water hammer (hydraulic shock) occurs when rapid valve closure converts kinetic energy of flowing liquid into pressure waves that travel through the system.

For two-phase gas-liquid flow, the Lockhart-Martinelli parameter X is used to characterize:

Answer: The ratio of frictional pressure drops of liquid and gas phases flowing alone

The Lockhart-Martinelli parameter X² is the ratio of frictional pressure drop of the liquid phase alone to that of the gas phase alone.

The continuity equation for steady incompressible flow through a converging nozzle states that:

Answer: The product of area and velocity is constant

Continuity for incompressible flow requires A₁V₁ = A₂V₂, so as area decreases, velocity must increase proportionally.

A pump's NPSH required (NPSHr) is exceeded when the system NPSH available (NPSHa) is lower than NPSHr, resulting in:

Answer: Cavitation within the pump

When NPSHa < NPSHr, the liquid pressure at the pump inlet drops below vapor pressure, causing cavitation—bubble formation and collapse that damages impeller.

The Colebrook-White equation is used in piping design to determine:

Answer: The Darcy-Weisbach friction factor for turbulent flow

The Colebrook-White equation implicitly relates friction factor to Reynolds number and relative roughness for turbulent flow in the transition and rough zones.