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 of the following is the SI unit of kinematic viscosity?
Answer: A
Kinematic viscosity is dynamic viscosity divided by density. Its SI unit is m²/s (or Stokes in CGS, where 1 Stoke = 10⁻⁴ m²/s).
Q.2Easy
A fluid flows through a pipe of diameter 0.1 m with velocity 2 m/s. If the kinematic viscosity is 1×10⁻⁶ m²/s, calculate the Reynolds number.
Answer: A
Re = (ρVD)/μ = VD/ν. Re = (2 × 0.1)/(1×10⁻⁶) = 0.2/(1×10⁻⁶) = 2×10⁵. Flow is turbulent.
Q.3Easy
Which equation relates pressure drop to velocity in laminar flow through pipes?
Answer: A
Hagen-Poiseuille equation (ΔP = 32μLV/D²) is specific for laminar flow. Darcy-Weisbach is general for both laminar and turbulent flows.
Q.4Medium
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.5Easy
A centrifugal pump operates at 1500 RPM. If the impeller diameter is 0.3 m, what is the tip speed?
Answer: A
Tip speed = πDN/60 = π × 0.3 × 601500 = 23.56 m/s (where N is in RPM).
Q.6Easy
In the Bernoulli equation, which term represents the pressure energy per unit volume?
Answer: C
The Bernoulli equation is P + ½ρV² + ρgz = constant. P itself is pressure energy per unit volume (not P/ρ which is pressure head).
Q.7Medium
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.8Medium
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.9Medium
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.10Easy
A fluid with dynamic viscosity 0.5 Pa·s and density 800 kg/m³ flows in a pipe. Its kinematic viscosity is:
Answer: A
ν = μ/ρ = 0.8005 = 6.25×10⁻⁴ m²/s.
Q.11Medium
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.12Medium
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.13Medium
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.14Easy
For a Newtonian fluid, shear stress (τ) is related to shear rate (dV/dy) by:
Answer: A
Newton's law of viscosity: τ = μ(dV/dy). Option B is power law (non-Newtonian), C is Bingham plastic model.
Q.15Medium
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).
In fluid mechanics, which dimensionless number represents the ratio of inertial forces to viscous forces?
Answer: A
Reynolds number Re = (Inertial forces)/(Viscous forces) = ρVD/μ. It characterizes flow regime (laminar vs turbulent).
Q.17Hard
For a given pipe and fluid, if the flow velocity doubles, the pressure drop in turbulent flow will approximately:
Answer: C
In turbulent flow, ΔP ∝ f × V^m where m is between 1.8-2 depending on friction factor variation. Not exactly V² due to changing friction factor with Re.
Q.18Medium
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.19Easy
Which pumping principle is used in a gear pump?
Answer: B
Gear pumps are positive displacement pumps. They move fixed volumes of fluid per rotation. Dynamic principle applies to centrifugal pumps.
Q.20Medium
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.
