The Rayleigh number (Ra) in natural convection is defined as Ra = Gr·Pr. When Ra < 10⁹ for vertical surfaces, the heat transfer is primarily:

The correct answer is B: Laminar. For Ra < 10⁹, natural convection remains laminar; transition to turbulence occurs around Ra ≈ 10⁹.

A heat pipe is used to transfer heat from an electronic component at 80°C to ambient air at 25°C through evaporation and condensation. What is the primary advantage of a heat pipe over conventional conduction cooling?

The correct answer is B: Effective thermal conductivity can be 1000 times higher than pure conduction. Heat pipes achieve very high effective thermal conductivity (often >1000 times that of copper) through the latent heat of evaporation and condensation of working fluid, making them ideal for high-power electronics cooling despite the small cross-sectional area.

What does the selectivity parameter in a competing reaction system measure?

The correct answer is B: The ratio of desired product to undesired product formation rates. Selectivity S = rate of desired product formation / rate of undesired product formation, used to optimize reactor conditions for maximum desired product yield

For a real gas obeying virial equation PV/nRT = 1 + B/V̄, the internal energy change with volume at constant T is:

The correct answer is D: Both B and C. For real gases, (∂U/∂V)_T ≠ 0. From thermodynamic relations: (∂U/∂V)_T = T(∂P/∂T)_V - P. Using virial equation gives (∂U/∂V)_T = T(dB/dT)/V̄². Non-ideal behavior affects internal energy.

The Thiele modulus (Φ) for a catalyst pellet determines whether the reaction is:

The correct answer is A: Diffusion-limited (high Φ) or kinetically-limited (low Φ). Φ = L√(k/D). When Φ >> 1, diffusion controls; when Φ

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Chemical Engineering
Mass Transfer

Process design, thermodynamics, reactions

22 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–22 of 22

Topics in Chemical Engineering

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

Q.21 Easy Mass Transfer

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

A Sc = μ/(ρ × D_AB)

B Sc = ρ × D_AB/μ

C Sc = μ × D_AB/ρ

D Sc = ρ/μ × D_AB

Correct Answer: A. Sc = μ/(ρ × D_AB)

EXPLANATION

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

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Q.22 Easy Mass Transfer

Which of the following is the correct definition of mass transfer coefficient in a binary diffusion system?

A Rate of mass transfer per unit area per unit concentration difference

B Total molar flux divided by pressure gradient

C Diffusivity multiplied by viscosity

D Molecular weight ratio of components

Correct Answer: A. Rate of mass transfer per unit area per unit concentration difference

EXPLANATION

Mass transfer coefficient (k) is defined as the rate of mass transfer per unit interfacial area per unit concentration difference, with units of length/time.

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