Fluid Mechanics Flashcards

A fluid with viscosity μ = 0.001 Pa·s flows between parallel plates 1 mm apart; the top plate moves at 1 m/s. What is the shear stress on the plates?

Answer: 1 Pa

τ = μ(du/dy) = 0.001 × (1/0.001) = 0.001 × 1000 = 1 Pa.

The specific gravity of a fluid is defined as the ratio of its density to the density of:

Answer: Water at 4°C

Specific gravity is the dimensionless ratio of a fluid's density to pure water's density at 4°C (1000 kg/m³).

For flow over a flat plate, the boundary layer thickness δ grows proportionally to:

Answer: x^(1/2)

For laminar flow over a flat plate, the Blasius solution gives δ ∝ x^(1/2) (or δ/x = 5/√Re_x).

Which valve type is best suited for throttling (flow control) applications?

Answer: Globe valve

Globe valves are specifically designed for throttling because their disc movement is perpendicular to flow, providing precise control.

A 6-inch schedule 40 steel pipe has a length of 100 ft and a friction factor f = 0.02. What is the Darcy-Weisbach head loss if water flows at 5 ft/s? (D = 0.5054 ft)

Answer: 1.54 ft

hf = f(L/D)(V²/2g) = 0.02×(100/0.5054)×(25/64.4) = 0.02×197.9×0.388 ≈ 1.54 ft.

The continuity equation for steady, incompressible flow in a pipe states that:

Answer: A₁V₁ = A₂V₂

For incompressible flow, density is constant, so mass conservation reduces to A₁V₁ = A₂V₂ (volumetric flow rate is constant).

In the Moody diagram, the fully turbulent (rough pipe) zone is characterized by:

Answer: Friction factor independent of Reynolds number

In the fully turbulent (complete turbulence) zone, the friction factor depends only on relative roughness, not Reynolds number.