The penetration theory for mass transfer assumes that:

The correct answer is A: Eddies expose fresh bulk fluid to the interface for short contact times. Penetration theory (Higbie) assumes eddies contact interface, remain for time θ, then submerge. More realistic than film theory for turbulent systems.

Which of the following statements about the thermal boundary layer in forced convection is incorrect?

The correct answer is D: Thermal boundary layer thickness is independent of thermal conductivity. Thermal boundary layer thickness δₜ depends on thermal conductivity through the thermal diffusivity (α = k/ρ·Cₚ). Statement D is incorrect as k directly affects the temperature profile and boundary layer development in the thermal region.

In fermentation processes, the Monod equation describes microbial growth rate kinetics. Which substrate concentration results in 90% of maximum growth rate?

The correct answer is A: 9 times K_s. From Monod equation: μ = (μ_max × [S])/(K_s + [S]). For μ = 0.9μ_max: [S] ≈ 9K_s

In a shell and tube heat exchanger, which configuration reduces the pressure drop while maintaining adequate heat transfer?

The correct answer is A: Increasing number of tube passes. Increasing the number of tube passes distributes the flow over more tubes, reducing the velocity in each tube and consequently reducing pressure drop while maintaining heat transfer area. This is a design optimization technique in shell and tube exchangers.

In the context of reaction kinetics, which statement best describes the rate-determining step (RDS) in a multi-step reaction mechanism?

The correct answer is B: It is the slowest step that controls the overall reaction rate. The rate-determining step is the slowest elementary step in the reaction mechanism, which governs the overall rate of the reaction regardless of its position in the sequence

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Chemical Engineering

Process design, thermodynamics, reactions

133 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 51–60 of 133

Topics in Chemical Engineering

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

Q.51 Easy Chemical Reaction Engineering

Which statement is correct about the residence time distribution (RTD) in an ideal plug flow reactor?

A All molecules spend different residence times

B All molecules spend the same residence time τ

C RTD follows Gaussian distribution

D RTD is exponential

Correct Answer: B. All molecules spend the same residence time τ

EXPLANATION

In ideal PFR, E(t) = δ(t-τ), meaning all molecules have identical residence time equal to τ

Test

Q.52 Easy Chemical Reaction Engineering

For a zero-order reaction, the integrated rate law is:

A [A] = [A]₀ - kt

B ln[A] = ln[A]₀ - kt

C 1/[A] = 1/[A]₀ + kt

D [A] = [A]₀e^(-kt)

Correct Answer: A. [A] = [A]₀ - kt

EXPLANATION

Zero-order integrated rate law: [A] = [A]₀ - kt, linear with time

Test

Q.53 Easy Chemical Reaction Engineering

A first-order reaction has a rate constant of 0.693 min⁻¹. What is its half-life?

A 1 minute

B 0.693 minutes

C 2 minutes

D 0.5 minutes

Correct Answer: A. 1 minute

EXPLANATION

For first-order reactions, t₁/₂ = 0.693/k = 0.693/0.693 = 1 minute

Test

Q.54 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.55 Easy Fluid Mechanics

A manometer shows a pressure difference of 50 mm of mercury (ρ_Hg = 13,600 kg/m³). What is the equivalent pressure difference in Pa?

A 6,667 Pa

B 6,800 Pa

C 13,333 Pa

D 6,580 Pa

Correct Answer: A. 6,667 Pa

EXPLANATION

ΔP = ρ_Hg × g × h = 13,600 × 9.81 × 0.05 = 6,667 Pa

Test

Q.56 Easy Fluid Mechanics

The friction factor 'f' in the Darcy-Weisbach equation depends on Reynolds number and relative roughness. For laminar flow (Re < 2300), friction factor is given by:

A f = 64/Re

B f = 0.316/Re⁰·²⁵

C f = 0.079/Re⁰·²⁵

D f = constant = 0.02

Correct Answer: A. f = 64/Re

EXPLANATION

For laminar flow in circular pipes, the Hagen-Poiseuille solution gives f = 64/Re. This is independent of roughness and applies for Re < 2300.

Test

Q.57 Easy Fluid Mechanics

A fluid flows through a horizontal pipe of diameter 0.1 m at a velocity of 3 m/s. If the pipe suddenly contracts to 0.05 m diameter, what is the velocity in the contracted section (assuming incompressible flow)?

A 6 m/s

B 12 m/s

C 3 m/s

D 1.5 m/s

Correct Answer: B. 12 m/s

EXPLANATION

By continuity equation: A₁V₁ = A₂V₂. π(0.1)²/4 × 3 = π(0.05)²/4 × V₂. V₂ = (0.01/0.0025) × 3 = 12 m/s

Test

Q.58 Easy Fluid Mechanics

Which of the following statements about laminar flow in a circular pipe is correct?

A Velocity profile is parabolic and maximum velocity occurs at pipe wall

B Velocity profile is parabolic and maximum velocity occurs at the center

C Velocity profile is rectangular and uniform across the section

D Velocity profile is triangular with zero at center

Correct Answer: B. Velocity profile is parabolic and maximum velocity occurs at the center

EXPLANATION

In laminar flow through circular pipes, the velocity distribution follows Hagen-Poiseuille flow with parabolic profile. Maximum velocity is at the centerline (V_max = 2×V_avg), and velocity is zero at the wall (no-slip condition).

Test

Q.59 Easy Fluid Mechanics

The Reynolds number for a fluid flow is defined as the ratio of inertial forces to viscous forces. For a pipe flow with diameter 0.05 m, velocity 2 m/s, and kinematic viscosity 1.0×10⁻⁶ m²/s, calculate the Reynolds number.

A 100,000

B 100

C 10,000

D 1,000

Correct Answer: A. 100,000

EXPLANATION

Re = (V×D)/ν = (2×0.05)/(1.0×10⁻⁶) = 0.1/(1.0×10⁻⁶) = 100,000

Test

Q.60 Easy Fluid Mechanics

In a fluid flow system, which of the following best represents the Bernoulli equation?

A P + ½ρV² + ρgZ = constant

B P/ρg + V²/2g + Z = constant

C ΔP = f(L/D)(ρV²/2)

D H = (P₂-P₁)/ρg + (V₂²-V₁²)/2g + (Z₂-Z₁)

Correct Answer: B. P/ρg + V²/2g + Z = constant

EXPLANATION

Bernoulli equation in head form: P/ρg + V²/2g + Z = constant. Option A is energy form, C is Darcy-Weisbach, D is modified form.

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