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

The correct answer is A: Rate of mass transfer per unit area per unit concentration difference. 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.

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 Fourier number (Fo = αt/L²) in unsteady-state conduction represents the ratio of:

The correct answer is A: Heat conducted to heat stored. Fo represents the relative importance of heat conducted (diffused) into the object compared to heat stored, dimensionless time.

In a finned tube heat exchanger, the overall surface effectiveness is 0.75. This means:

The correct answer is A: 75% of the theoretical maximum heat transfer is achieved. Overall surface effectiveness accounts for both fin and base surface contributions. A value of 0.75 indicates that 75% of the theoretical maximum heat transfer (assuming entire surface at base temperature) is actually achieved due to fin efficiency and geometric factors.

The heat capacity at constant pressure Cₚ is always greater than heat capacity at constant volume Cᵥ because:

The correct answer is B: At constant P, additional heat is needed for expansion work. Cₚ - Cᵥ = R (for ideal gas). At constant P, supplied heat does both internal energy and expansion work. At constant V, all heat goes to internal energy only.

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Chemical Engineering
Heat Transfer

Process design, thermodynamics, reactions

25 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–25 of 25

Topics in Chemical Engineering

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

Q.21 Easy Heat Transfer

The thermal diffusivity (α) has dimensions of which of the following?

A Length²/Time

B Length/Time²

C Energy/(Mass·Temperature)

D Energy/(Time·Length)

Correct Answer: A. Length²/Time

EXPLANATION

Thermal diffusivity α = k/(ρ·C_p) has dimensions L²/t, representing how fast thermal disturbances propagate through a material.

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Q.22 Easy Heat Transfer

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

A Increases with temperature

B Decreases with temperature

C Remains constant

D First increases then decreases

Correct Answer: B. Decreases with temperature

EXPLANATION

For most pure metals, thermal conductivity decreases with increasing temperature due to increased lattice vibrations causing phonon scattering.

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Q.23 Easy Heat Transfer

Which dimensionless number represents the ratio of buoyancy forces to viscous forces in natural convection?

A Grashof number (Gr)

B Rayleigh number (Ra)

C Nusselt number (Nu)

D Prandtl number (Pr)

Correct Answer: A. Grashof number (Gr)

EXPLANATION

Grashof number (Gr = gβΔT L³/ν²) represents the ratio of buoyancy to viscous forces. Ra = Gr × Pr combines both effects.

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Q.24 Easy Heat Transfer

In heat conduction through a composite wall, the overall heat transfer rate is determined by which principle?

A Ohm's law analogy

B Kirchhoff's law

C Fourier's law only

D Stefan-Boltzmann law

Correct Answer: A. Ohm's law analogy

EXPLANATION

The thermal resistance network (Ohm's law analogy) is used where total thermal resistance equals the sum of individual resistances in series for composite walls.

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Q.25 Easy Heat Transfer

Which of the following is the SI unit of thermal conductivity?

A W/(m·K)

B W/(m²·K)

C J/(s·m·K)

D cal/(s·cm·°C)

Correct Answer: A. W/(m·K)

EXPLANATION

Thermal conductivity is expressed as W/(m·K) in SI units, equivalent to J/(s·m·K). This represents heat flow rate per unit area per unit temperature gradient.

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