Which dimensionless number characterizes the relative importance of inertial forces to viscous forces in fluid flow?
Answer: B
Reynolds number (Re = ρVD/μ) represents the ratio of inertial to viscous forces
Q.242Medium
In turbulent flow through a pipe, the friction factor can be estimated using the Colebrook-White equation. For smooth pipes at high Reynolds numbers, which equation applies?
Answer: B
For smooth pipes at high Re, Blasius correlation (f = 0.316/Re^0.25) is used with Darcy-Weisbach equation
Q.243Medium
A fluid flows through a sudden expansion from pipe diameter D₁ = 0.05 m to D₂ = 0.1 m with velocity V₁ = 4 m/s. Calculate the pressure recovery coefficient (Cp) for the expansion.
Answer: B
For sudden expansion, Cp = 1 - (A₁/A₂)² = 1 - (D₁/D₂)⁴ = 1 - (0.005.1)⁴ = 0.9375, but accounting for losses, recovery coefficient ≈ 0.56
Q.244Medium
In an orifice meter with diameter ratio β = 0.6, what is the typical discharge coefficient (Cd) used for flow calculations?
Answer: B
For sharp-edged orifices, discharge coefficient typically ranges from 0.60-0.65, with 0.61 being standard for β = 0.6
Q.245Medium
A rotameter (variable area flowmeter) is used for gas flow measurement. The float rise in the tube depends on which factor?
Answer: B
Rotameter float position equilibrium depends on drag force, buoyancy, and weight - all affected by fluid viscosity and density
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Q.246Medium
For compressible isothermal flow through a horizontal pipe, which statement is correct?
Answer: A
In isothermal compressible flow with friction, pressure decreases while velocity increases due to fluid expansion
Q.247Easy
In a reciprocating pump with piston diameter D = 0.1 m and stroke length L = 0.2 m operating at 60 RPM, calculate the theoretical displacement per revolution.
Answer: A
Displacement = π/4 × D² × L = π/4 × (0.1)² × 0.2 = 0.00157 m³ per revolution
Q.248Medium
Which of the following conditions must be satisfied for cavitation to occur in a centrifugal pump?
Answer: B
Cavitation occurs when available NPSH is less than required NPSH, causing vapor bubble formation
Q.249Medium
In open channel flow, the Froude number is defined as Fr = V/√(gD_h), where D_h is the hydraulic depth. When Fr = 1, the flow is classified as:
Answer: B
Fr = 1 defines critical flow; Fr < 1 is subcritical; Fr > 1 is supercritical
Q.250Medium
For flow measurement in a Venturi tube with diameter ratio (D₁/D₂) = 2, what is the diameter ratio for minimum vibration and noise?
Answer: C
Optimal Venturi throat diameter ratio is typically 2.5-3.0 for smooth operation and minimal vibration
Q.251Hard
A gas flows through a convergent nozzle. At what condition does maximum mass flow rate occur in the nozzle exit?
Answer: B
For convergent nozzles, mass flow becomes independent of downstream pressure when throat reaches sonic conditions (M = 1)
Q.252Hard
The Moody diagram is used to determine friction factor in pipes. For which flow regime is the Darcy friction factor independent of Reynolds number?
Answer: C
In fully turbulent flow in rough pipes, friction factor depends only on relative roughness, not Reynolds number
Q.253Hard
In boundary layer theory, the displacement thickness (δ*) represents which physical concept?
Answer: B
Displacement thickness is the distance the external streamline is displaced due to the reduction in flow velocity within the boundary layer
Q.254Medium
A fluid with kinematic viscosity ν = 2×10⁻⁵ m²/s flows over a flat plate at velocity V = 10 m/s. At what plate length does transition from laminar to turbulent flow occur (Re_critical ≈ 5×10⁵)?
Answer: B
Re = Vx/ν; 5×10⁵ = 10×x/(2×10⁻⁵); x = 1.0 m
Q.255Medium
In a settling tank (clarifier) with depth H = 2 m, overflow rate = 1 m³/m²·h, and settling velocity of particles = 0.02 m/min, will the particles settle completely?
Answer: A
Settling velocity = 0.02 m/min = 1.2 m/h. Overflow rate = 1 m³/m²·h means rise velocity = 1 m/h < 1.2 m/h, so particles will settle
Q.256Medium
For a centrifugal pump, cavitation can be prevented by maintaining NPSH above the required value. In 2024-25 industrial practice, what is the typical margin kept above calculated NPSH_required?
Answer: C
Modern pump design standards recommend 20-30% safety margin above NPSH_required to ensure cavitation-free operation
Q.257Medium
A submersed weir has crest length L = 1.5 m and head H = 0.6 m. Using Francis formula for suppressed weir (Q = 1.84 LH^1.5), calculate discharge.
In pipe flow with fittings, which fitting typically causes the highest pressure loss coefficient (K)?
Answer: D
Sudden contraction typically has K ≈ 0.5, while 90° elbow has K ≈ 0.9, but sudden expansion losses are highest at K > 1.0 for significant diameter changes
Q.259Easy
A fluid flows through a circular pipe of diameter 50 mm at a velocity of 2 m/s. If the kinematic viscosity is 1×10⁻⁵ m²/s, calculate the Reynolds number and identify the flow regime.
Answer: A
Reynolds number = (ρVD)/μ = VD/ν = (2 × 0.05)/(1×10⁻⁵) = 10,000. Flow is turbulent for Re > 4,000.
Q.260Easy
Which of the following dimensionless numbers represents the ratio of inertial forces to viscous forces in fluid flow?
Answer: B
Reynolds number (Re) = inertial forces/viscous forces. It is the fundamental dimensionless number in fluid mechanics.
