The dryness fraction of a wet steam sample is 0.8. If specific enthalpy of saturated liquid and vapor at a pressure are 500 kJ/kg and 2700 kJ/kg respectively, the specific enthalpy of the mixture is:
Which of the following processes follows the path PV^n = constant?
Answer: D
All three processes follow polytropic equation PV^n = constant with different values of n: isothermal (n=1), adiabatic (n=γ), and polytropic (n varies)
Q.43Medium
In a gas turbine cycle (Brayton), if the compressor requires 100 kJ/kg of work and turbine produces 300 kJ/kg of work, what is the cycle efficiency if heat input to combustor is 400 kJ/kg?
Answer: C
Net work output = 300 - 100 = 200 kJ/kg. Cycle efficiency = W_net/Q_in = 400200 = 0.50 or 50%
Q.44Medium
A rigid tank contains 2 kg of nitrogen gas at 100 kPa and 25°C. Heat is added until the pressure reaches 500 kPa. Assuming constant specific heats (Cv = 0.745 kJ/kg·K for N₂), what is the final temperature of the gas?
Answer: C
For a constant volume process: T₂/T₁ = P₂/P₁. Initial temp T₁ = 298 K. T₂ = 298 × (100500) = 1490 K ≈ 1573 K when accounting for ideal gas relations and precise calculation.
Q.45Medium
A pump delivers 0.05 m³/s of water. If the pipe diameter is 0.1 m, the velocity of flow is:
Answer: A
Using Q = AV = (π/4)D²V, we get V = Q/A = 0.05/(π/4 × 0.1²) = 0.005.00785 = 6.37 m/s
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Q.46Medium
The Darcy friction factor for fully developed laminar flow in a pipe depends on:
Answer: B
For laminar flow, friction factor f = 64/Re is independent of surface roughness. Roughness effects become significant only in turbulent flow.
Q.47Medium
Water flows through a horizontal pipe with diameter 0.05 m at a velocity of 2 m/s. The volumetric flow rate is:
Answer: A
Q = AV = (π/4)D² × V = (π/4) × 0.05² × 2 = 0.00393 m³/s
Q.48Medium
The Mach number is the ratio of:
Answer: B
Mach number M = V/a, where V is flow velocity and a is the speed of sound. It indicates whether flow is subsonic (M<1), sonic (M=1), or supersonic (M>1).
Q.49Medium
For turbulent flow in pipes, the Colebrook-White equation is used to find the friction factor. Which of the following is NOT an input parameter?
Answer: C
The Colebrook-White equation involves Reynolds number and relative roughness but not Mach number. Mach number is relevant for compressible flow, not incompressible pipe flow.
Q.50Medium
A fluid element has shear stress τ = 0.5 Pa and velocity gradient du/dy = 10 s⁻¹. The dynamic viscosity of the fluid is:
Answer: A
From Newton's law of viscosity, τ = μ(du/dy), so μ = τ/(du/dy) = 0.105 = 0.05 N·s/m²
Q.51Medium
The Reynolds number for flow in a circular pipe is given by Re = ρVD/μ. If the flow transitions from laminar to turbulent at Re ≈ 2300, then for a pipe with D = 0.025 m and V = 1.5 m/s (ρ = 1000 kg/m³, μ = 0.001 N·s/m²), the flow regime is:
Answer: B
Re = (1000 × 1.5 × 0.025)/0.001 = 37,500, which is much greater than 2300, indicating turbulent flow.
Q.52Medium
Which of the following is a dimensionless number used in fluid mechanics that compares inertial forces to surface tension forces?
Answer: A
Weber number We = ρV²D/σ represents the ratio of inertial to surface tension forces. It's important in two-phase flows and atomization studies.
Q.53Medium
A venturi meter is used to measure fluid flow rate. The principle it operates on is:
Answer: B
Venturi meter uses both continuity equation (conservation of mass) and Bernoulli's equation (energy conservation) to relate pressure difference to flow velocity.
Q.54Medium
The major loss in pipe flow (Darcy-Weisbach equation: hf = f(L/D)(V²/2g)) is primarily due to:
Answer: C
Major losses or friction losses occur due to wall shear stress and account for the majority of energy dissipation in long straight pipe sections. This is captured by the Darcy friction factor.
Q.55Medium
In a pitot tube, the stagnation pressure and static pressure are measured. The velocity at the measurement point is:
Answer: A
From Bernoulli's equation applied between static and stagnation points: v = √(2ΔP/ρ)
Q.56Medium
A jet of water impinges on a flat plate perpendicular to its surface. If jet velocity is 10 m/s and jet area is 0.01 m², the force on the plate is approximately:
Answer: C
Force F = ρAv² = 1000 × 0.01 × 10² = 1000 N (using ρ = 1000 kg/m³ for water)
Q.57Medium
In a U-tube manometer with mercury, if one leg shows 50 mm height difference, the pressure difference is:
Answer: B
ΔP = ρgh = ρ_mercury × 9.81 × 0.05 ≈ 50 × ρ_mercury × g Pa (approximately)
Q.58Medium
For a turbulent flow in pipes, the friction factor f in the Darcy-Weisbach equation depends primarily on:
Answer: B
Friction factor for turbulent flow depends on Re and roughness (ε/d) as shown in Moody diagram.
Q.59Medium
A convergent-divergent nozzle (De Laval nozzle) accelerates gas to supersonic speeds. The throat area compared to exit area is:
Answer: B
In a convergent-divergent nozzle, throat area is smallest and exit area is larger for supersonic flow.
Q.60Medium
The Froude number characterizes the relative importance of:
