What is the Schmidt number (Sc) in mass transfer? Select the most accurate definition.

The correct answer is A: Sc = μ/(ρ × D_AB). Schmidt number is Sc = kinematic viscosity/diffusivity = μ/(ρ × D_AB). It is a dimensionless number analogous to Prandtl number in heat transfer.

The mass transfer rate from a solid sphere dissolving in a flowing liquid can be described using the Ranz-Marshall correlation. Which parameter is NOT included in this correlation?

The correct answer is C: Froude number. The Ranz-Marshall correlation for a sphere is Sh = 2 + 0.6 Re^(1/2) Sc^(1/3). Froude number (related to gravity effects) is not part of this correlation.

Which of the following best describes the behavior of thermal conductivity with temperature for most metals?

The correct answer is B: Decreases with temperature. For most pure metals, thermal conductivity decreases with increasing temperature due to increased lattice vibrations causing phonon scattering.

A fluid with dynamic viscosity 0.5 Pa·s and density 800 kg/m³ flows in a pipe. Its kinematic viscosity is:

The correct answer is A: 6.25×10⁻⁴ m²/s. ν = μ/ρ = 0.5/800 = 6.25×10⁻⁴ m²/s.

A centrifugal pump has an impeller diameter of 0.3 m rotating at 1500 RPM. Calculate the peripheral speed of the impeller tip.

The correct answer is A: 23.56 m/s. Peripheral speed = πDN/60 = π × 0.3 × 1500/60 = 23.56 m/s

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Chemical Engineering
Fluid Mechanics

Process design, thermodynamics, reactions

100 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 100

Topics in Chemical Engineering

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

Q.1 Medium Fluid Mechanics

For a horizontal pipe with diameter variation from D₁ to D₂, if pressure difference is ΔP and ignoring losses, the velocity ratio V₁/V₂ is:

A D₂/D₁

B (D₂/D₁)²

C 1.0 (equal)

D Depends on viscosity

Correct Answer: B. (D₂/D₁)²

EXPLANATION

By continuity: A₁V₁ = A₂V₂. Since A = πD²/4, we get V₁/V₂ = A₂/A₁ = (D₂/D₁)². Pressure difference from Bernoulli validates this for incompressible flow.

Test

Q.2 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.3 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.4 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.5 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.6 Easy Fluid Mechanics

For a fluid flowing over a submerged object, the drag force is given by F_D = (1/2)ρV²AC_D. If velocity doubles and drag coefficient remains constant, drag force increases by a factor of:

A 2

B 4

C 8

D 16

Correct Answer: B. 4

EXPLANATION

F_D ∝ V². When V doubles (V₂ = 2V₁), F_D increases by factor of (2)² = 4

Test

Q.7 Medium Fluid Mechanics

The Moody diagram is used to determine friction factor for pipe flow. It shows that friction factor increases with:

A Increasing Reynolds number for all conditions

B Increasing relative roughness and decreasing Reynolds number

C Decreasing Reynolds number only

D Temperature decrease

Correct Answer: B. Increasing relative roughness and decreasing Reynolds number

EXPLANATION

In the Moody diagram, friction factor decreases with increasing Re in laminar region. In turbulent region, f increases with relative roughness (ε/D) and slightly decreases with increasing Re for rough pipes.

Test

Q.8 Medium Fluid Mechanics

A hydraulic jump occurs in open channel flow when:

A Froude number decreases gradually

B Supercritical flow (Fr > 1) transitions to subcritical flow (Fr < 1)

C Flow remains at critical condition (Fr = 1)

D Depth remains constant throughout the channel

Correct Answer: B. Supercritical flow (Fr > 1) transitions to subcritical flow (Fr < 1)

EXPLANATION

Hydraulic jump is an abrupt, turbulent transition from supercritical to subcritical flow. Energy is dissipated during this process, causing a sudden rise in water surface.

Test

Q.9 Medium Fluid Mechanics

For compressible flow through a nozzle, if pressure drops significantly and reaches sonic conditions, the Mach number at that point is:

A M = 0 (subsonic)

B M = 0.5

C M = 1.0 (sonic)

D M > 1.0 (supersonic)

Correct Answer: C. M = 1.0 (sonic)

EXPLANATION

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.

Test

Q.10 Medium Fluid Mechanics

In boundary layer theory on a flat plate, the displacement thickness δ* represents:

A The distance from wall to edge where velocity becomes zero

B The distance by which the free stream is displaced due to boundary layer formation

C The maximum thickness of the boundary layer

D The distance where velocity reaches 99% of free stream velocity

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

EXPLANATION

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.

Test

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