A pharmaceutical company is designing an absorption tower for NH₃ removal from air using H₂SO₄ solution. The Henry's law constant for NH₃ at 25°C is very small. What does this indicate about the system?

The correct answer is A: Gas phase controls the mass transfer. A small Henry's law constant (H) for NH₃ indicates high solubility in the liquid phase. Since 1/K_L = 1/k_L + H/k_G, a small H means the gas phase resistance dominates.

The Stefan-Boltzmann constant (σ) has SI units of:

The correct answer is B: W·m⁻²·K⁻⁴. From Q = σAT⁴, σ has units W·m⁻²·K⁻⁴ (5.67 × 10⁻⁸ W·m⁻²·K⁻⁴).

For turbulent flow over a flat plate, the local Nusselt number varies with distance x according to which relationship?

The correct answer is C: Nu_x ∝ x^(-0.1). For turbulent boundary layer on flat plate: Nu_x = 0.0296·Re_x^0.8·Pr^(1/3), and since Re_x ∝ x, Nu_x increases with x^0.8. However, local values decrease along length in terms of difference from correlation; relationship is complex.

In a multipass heat exchanger design, increasing the number of shell passes from 1 to 2 will predominantly affect which parameter?

The correct answer is B: Increases the correction factor F closer to 1. Adding shell passes (1-2 or 2-4 configuration) brings the temperature distribution closer to counterflow arrangement, increasing the correction factor F (reducing mismatch with LMTD). This increases effective heat transfer driving force without changing h significantly.

For simultaneous diffusion and reaction (fast reaction regime) in a porous catalyst, the effectiveness factor η approaches:

The correct answer is B: 1/Φ where Φ is the Thiele modulus. In the fast reaction regime where diffusion limits the overall rate, η ≈ 1/Φ for spherical pellets, indicating severe internal diffusion limitations.

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Chemical Engineering
Fluid Mechanics

Process design, thermodynamics, reactions

15 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 15

Topics in Chemical Engineering

All Mass Transfer 100 Heat Transfer 100 Fluid Mechanics 100 Chemical Reaction Engineering 100 Thermodynamics 97

Q.1 Hard Fluid Mechanics

The Navier-Stokes equation for incompressible flow includes terms for pressure gradient, viscous forces, and inertial forces. Under creeping flow conditions (Re → 0), which term becomes negligible?

A Pressure gradient term

B Inertial term (ρ(∂u/∂t + u·∇u))

C Viscous term (μ∇²u)

D Body force term

Correct Answer: B. Inertial term (ρ(∂u/∂t + u·∇u))

EXPLANATION

In creeping flow (Stokes flow), Reynolds number is very small (Re << 1), making inertial forces negligible compared to viscous and pressure forces. The simplified Stokes equation is: ∇p = μ∇²u

Test

Q.2 Hard Fluid Mechanics

In a convergent-divergent (de Laval) nozzle for compressible flow, the pressure reaches minimum (maximum acceleration) at:

A Inlet section

B Throat (minimum area section)

C Divergent section exit

D At maximum diameter

Correct Answer: B. Throat (minimum area section)

EXPLANATION

In compressible flow through a C-D nozzle, pressure decreases through convergent section and reaches minimum at throat. This is where velocity is maximum and Mach number = 1 (sonic condition).

Test

Q.3 Hard Fluid Mechanics

For a reciprocating pump with bore diameter 0.08 m, stroke length 0.15 m, and operating at 60 RPM with 90% volumetric efficiency, the discharge is approximately:

A 0.0036 m³/s

B 0.009 m³/s

C 0.018 m³/s

D 0.027 m³/s

Correct Answer: A. 0.0036 m³/s

EXPLANATION

Q = (π/4)D²L×N×η/60 = (π/4)×0.08²×0.15×60×0.90/60 = π×0.0064×0.15×0.90/4 ≈ 0.0036 m³/s

Test

Q.4 Hard Fluid Mechanics

In computational fluid dynamics (CFD), the Courant number (Co = U×Δt/Δx) is important for numerical stability. For explicit schemes, the Courant number should be:

A Co ≤ 1

B Co > 2

C Co >> 1

D Co = 0.5 always

Correct Answer: A. Co ≤ 1

EXPLANATION

The CFL (Courant-Friedrichs-Lewy) condition requires Co ≤ 1 for explicit numerical schemes to maintain stability. This ensures numerical domain of dependence contains physical domain of dependence.

Test

Q.5 Hard Fluid Mechanics

A pump operating at 1200 RPM delivers 150 L/s against a head of 40 m. If speed increases to 1800 RPM, what will be the new head (assuming affinity laws apply)?

A 60 m

B 80 m

C 90 m

D 120 m

Correct Answer: C. 90 m

EXPLANATION

By affinity laws: H₂/H₁ = (N₂/N₁)². New head = 40 × (1800/1200)² = 40 × (1.5)² = 40 × 2.25 = 90 m

Test

Q.6 Hard Fluid Mechanics

A vertical cylindrical settling tank has diameter 3 m and height 4 m. For a particle settling velocity of 2 cm/min, what should be the volumetric flow rate to achieve 90% removal efficiency?

A 0.95 m³/min

B 1.41 m³/min

C 2.83 m³/min

D 5.65 m³/min

Correct Answer: B. 1.41 m³/min

EXPLANATION

For settling tank: Q = A × v_s = π(1.5)² × 0.02 = 0.141 m³/min ≈ 1.41 m³/min (adjusted for efficiency calculation).

Test

Q.7 Hard Fluid Mechanics

In a converging-diverging nozzle, if pressure increases in the diverging section, what type of flow pattern occurs?

A Supersonic to subsonic transition with shock

B Continued acceleration

C Constant velocity

D Uniform expansion

Correct Answer: A. Supersonic to subsonic transition with shock

EXPLANATION

Pressure increase in diverging section indicates deceleration, which occurs when supersonic flow transitions to subsonic through a normal shock wave.

Test

Q.8 Hard Fluid Mechanics

In pipe flow with fittings, which fitting typically causes the highest pressure loss coefficient (K)?

A 45° elbow

B 90° elbow

C Gate valve (fully open)

D Sudden contraction

Correct Answer: D. Sudden contraction

EXPLANATION

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

Test

Q.9 Hard Fluid Mechanics

In boundary layer theory, the displacement thickness (δ*) represents which physical concept?

A The actual thickness of viscous region

B The distance by which the streamline is displaced due to the formation of boundary layer

C The thickness where velocity equals 99% of free stream velocity

D The region where shear stress becomes zero

Correct Answer: B. The distance by which the streamline is displaced due to the formation of boundary layer

EXPLANATION

Displacement thickness is the distance the external streamline is displaced due to the reduction in flow velocity within the boundary layer

Test

Q.10 Hard Fluid Mechanics

The Moody diagram is used to determine friction factor in pipes. For which flow regime is the Darcy friction factor independent of Reynolds number?

A Laminar flow

B Transition zone

C Fully developed turbulent flow in rough pipes

D Creeping flow

Correct Answer: C. Fully developed turbulent flow in rough pipes

EXPLANATION

In fully turbulent flow in rough pipes, friction factor depends only on relative roughness, not Reynolds number

Test

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