Chemical Engineering questions for GATE and PSU exams are built on a handful of core subjects applied in many ways. Practice spans fluid mechanics, heat transfer, mass transfer, chemical reaction engineering, thermodynamics, process control and instrumentation, and plant design economics. Numerical solutions carry the assumptions written out, because the assumption is usually what separates a correct answer from a plausible one.
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
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.
