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.
For turbulent flow in rough pipes at high Reynolds numbers, which friction factor equation is most applicable?
Answer: B
Colebrook-White equation is implicit but accurate for all turbulent regimes including rough pipes. For very rough pipes at high Re, relative roughness dominates.
Q.2Medium
Water flows through a venturimeter with inlet diameter 0.1 m and throat diameter 0.05 m. The pressure difference is 5 kPa. Assuming ideal flow, calculate the velocity at the inlet (ρ = 1000 kg/m³).
Answer: B
Using continuity and Bernoulli: V₁ = √[2ΔP/(ρ(A₁²/A₂² - 1))]. With area ratio 4, V₁ = √[2×5000/(1000×15)] = 2.88 m/s.
Q.3Medium
Which type of pump is most suitable for high-head, low-flow applications?
Answer: B
Reciprocating pumps (piston/plunger) are positive displacement pumps ideal for high-head, low-flow conditions. Centrifugal pumps suit high-flow, low-head applications.
Q.4Medium
What is the relationship between Fanning friction factor (f) and Darcy friction factor (fD)?
Answer: A
Fanning factor is ¼ of Darcy factor: f = fD/4. Both relate pressure drop to flow, but through different equations.
Q.5Medium
In a packed bed, if particle diameter increases while maintaining constant bed porosity and superficial velocity, the pressure drop will:
Answer: B
Ergun equation: ΔP ∝ (1-ε)²V/(ε³dp²). Pressure drop is inversely proportional to dp². Larger particles = lower pressure drop.
Q.6Medium
The drag coefficient for a sphere in creeping flow (Re < 0.1) is given by:
Answer: A
For creeping flow (Stokes law), CD = 24/Re. This is valid for Re < 0.1. For higher Re, additional terms and constant drag apply.
Q.7Medium
Which of the following statements about orifice plates is TRUE?
Answer: B
Vena contracta is the region of minimum cross-section and maximum velocity after the orifice. Pressure drop is proportional to V², discharge coefficient depends on Re, and recovery is incomplete.
Q.8Medium
A pump must deliver 50 m³/h against a total head of 30 m. Calculate the theoretical power required (assuming water, g = 10 m/s²).
A manometer shows a mercury height difference of 0.2 m for air flow in a duct. Calculate the pressure difference (ρHg = 13600 kg/m³, g = 10 m/s²).
Answer: C
ΔP = ρgh = 13600 × 10 × 0.2 = 27200 Pa. But if measured in cm (0.002 m): ΔP = 272 Pa. Given context, likely 0.2 m = 20 cm, so ΔP = 2720 Pa.
Q.10Medium
For incompressible flow through a converging nozzle, if the inlet area is 4 times the outlet area and inlet velocity is 5 m/s, the outlet velocity will be:
Answer: C
By continuity equation: A₁V₁ = A₂V₂. If A₁ = 4A₂, then V₂ = 4V₁ = 4 × 5 = 20 m/s.
Q.11Medium
A centrifugal pump delivers 30 m³/h of water. The inlet pressure is -0.2 bar (gauge) and outlet pressure is 8 bar (gauge). If the outlet is 2m higher than inlet, calculate the total head in meters. (Consider g = 9.81 m/s², ρ = 1000 kg/m³)
Answer: B
Total head H = (P_out - P_in)/(ρg) + (v_out² - v_in²)/(2g) + z_out - z_in = (800000 + 20000)/(1000×9.81) + 2 = 82.26 + 2 = 84.26 m ≈ 84.2 m
Q.12Medium
For a sharp-edged orifice, the coefficient of contraction (Cc) typically ranges between:
Answer: B
The coefficient of contraction for sharp-edged orifices is typically 0.60-0.65 due to the vena contracta effect where the jet contracts after leaving the orifice.
Q.13Medium
In the Hagen-Poiseuille equation for laminar flow through a circular pipe, the volumetric flow rate is proportional to:
Answer: D
Hagen-Poiseuille equation: Q = (πΔPd⁴)/(128μL), showing Q ∝ d⁴. This is why small diameter pipes are very sensitive to pressure drops.
Q.14Medium
A ball of diameter 5 cm falls through glycerin at terminal velocity. If the Stokes drag coefficient Cd is used, this indicates:
Answer: B
Stokes law (Cd = 24/Re) applies for creeping flow where Re < 1. For low Reynolds numbers, viscous forces dominate over inertial forces.
Q.15Medium
The Darcy-Weisbach equation relates friction loss to flow parameters. The friction factor f for turbulent flow in smooth pipes is given by:
Answer: D
For turbulent flow in smooth pipes, the Blasius equation is explicit and simpler, while Colebrook-White is implicit but more accurate. Both are used depending on applications.
Q.16Medium
For flow over a flat plate, the drag force depends on velocity according to:
Answer: B
Drag force F_d = 0.5 × ρ × V² × A × Cd. The V² dependence comes from dynamic pressure (½ρV²). This applies to both skin friction and pressure drag.
Q.17Medium
In a siphon arrangement, what is the maximum theoretical height from which water can be siphoned up using atmospheric pressure?
Answer: C
The maximum height is approximately 10.3 m (or one atmosphere height), determined by h = P_atm/(ρg) = 101325/(1000 × 9.81) = 10.33 m. Friction losses reduce this in practice.
Q.18Medium
For a venturimeter operating with water flow, the pressure at the throat is found to be lower than upstream. This pressure drop is used to:
Answer: A
Venturimeter uses Bernoulli's equation principle. The pressure difference between throat and upstream is related to flow velocity and can be used to calculate the volumetric flow rate.
Q.19Medium
In a pitot tube application, the stagnation point pressure exceeds static pressure by an amount equal to:
Answer: B
From Bernoulli's equation: P_stagnation - P_static = ½ρV². This dynamic pressure difference is measured by pitot tubes to determine local flow velocity.
Q.20Medium
For a long horizontal pipeline with incompressible fluid, the pressure loss due to friction increases when:
Answer: C
From Darcy-Weisbach: h_f = f(L/D)(V²/2g). Friction loss is proportional to length and approximately proportional to V² (in turbulent flow, f decreases slightly with V).
