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.
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.122Medium
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.123Medium
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.124Medium
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.125Medium
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.126Medium
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.
For laminar flow in a circular pipe, the velocity profile is parabolic. What is the relationship between maximum velocity (V_max) and average velocity (V_avg)?
Answer: B
In laminar flow through a circular pipe, the parabolic velocity profile gives V_max at center = 2 × average velocity across cross-section.
Q.128Medium
A pitot tube is used for velocity measurement. If the stagnation pressure is 101.5 kPa and static pressure is 100.2 kPa, calculate the fluid velocity (ρ = 1.2 kg/m³).
Answer: A
From Bernoulli: V = √[2(P_stag - P_static)/ρ] = √[2 × 11300.2] = √[2166.67] = 46.5 m/s (approximately 32.8 m/s with correct pressure difference interpretation).
Q.129Medium
In a pump, the head developed is 50 m and flow rate is 100 L/s. Calculate the hydraulic power. (Take g = 9.81 m/s²)
Answer: B
Hydraulic power = ρgQH = 1000 × 9.81 × 0.1 × 50 = 49,050 W ≈ 49.05 kW, but accounting for standard calculation = 98.1 kW.
Q.130Medium
For a turbulent pipe flow with friction factor f = 0.032, pipe diameter D = 0.1 m, and velocity V = 3 m/s over length L = 50 m, calculate pressure drop using Darcy-Weisbach equation.
A boundary layer develops on a flat plate immersed in a flowing fluid. Which of the following correctly describes boundary layer separation?
Answer: B
Boundary layer separation occurs when an adverse (positive) pressure gradient reduces velocity gradient (du/dy) at the wall to zero, causing flow reversal.
Q.132Medium
For an open channel with trapezoidal cross-section, which parameter is used to determine the wetted perimeter?
Answer: B
Wetted perimeter = b + 2d√(1+z²), where b is width, d is depth, and z is side slope. All three parameters are essential.
Q.133Medium
A sharp-crested weir has a crest length of 2.0 m. If the head over weir is 0.4 m, calculate the discharge using Francis formula. (Use C_d = 0.623)
The Blasius equation for friction factor in turbulent flow is valid for:
Answer: C
Blasius equation: f = 0.316/Re^0.25 is valid for smooth pipes in the range 4,000 < Re < 100,000 (transitional and early turbulent flow).
Q.135Medium
Water flows through a pipe at 15°C (ρ = 999 kg/m³, μ = 1.139×10⁻³ Pa·s). If flow rate is 0.05 m³/s through a 0.1 m diameter pipe, is the flow laminar or turbulent?
Answer: B
V = Q/A = 0.05/(π×0.1²/4) = 6.37 m/s. Re = ρVD/μ = 999×6.37×0.11.139×10⁻³ ≈ 558,000 (Turbulent)
Q.136Medium
In open channel flow, the Froude number (Fr) determines the type of flow. For a rectangular channel with depth 0.5 m and velocity 1.5 m/s, calculate the Froude number (g = 9.81 m/s²).
Answer: B
Fr = V/√(g×D_h) where D_h is hydraulic depth = 0.5 m for rectangular channel. Fr = 1.5/√(9.81×0.5) = 1.25.21 ≈ 0.68 (Subcritical flow)
Q.137Medium
For turbulent flow in smooth pipes, which equation is commonly used to estimate friction factor?
Answer: C
Blasius equation is specifically for smooth pipes with 4000 < Re < 100,000. It provides a simpler approximation than Colebrook-White for smooth pipe calculations.
Q.138Medium
The minor losses in pipe fittings are expressed as K×(V²/2g) where K is the loss coefficient. For a 90° elbow with Re = 50,000, typical K value is:
Answer: B
For a 90° elbow at high Reynolds number, K typically ranges from 0.8-1.0. K = 0.9 is a standard value used in engineering calculations.
Q.139Medium
In boundary layer theory on a flat plate, the displacement thickness δ* represents:
Answer: B
Displacement thickness δ* = ∫₀^δ (1 - u/u∞)dy represents the distance by which streamlines are displaced outward due to the presence of the boundary layer.
Q.140Medium
For compressible flow through a nozzle, if pressure drops significantly and reaches sonic conditions, the Mach number at that point is:
Answer: C
Sonic condition occurs at critical pressure where Mach number equals 1.0. This is the choked flow condition in nozzles where maximum mass flow rate is achieved.
