In an isothermal CSTR, if feed concentration C_A0 = 10 mol/m³ and outlet concentration C_A = 2 mol/m³, conversion is:

The correct answer is B: 0.8 or 80%. Conversion X = (C_A0 - C_A)/C_A0 = (10-2)/10 = 0.8 = 80%

In the design of a steam generator, the pinch point is the minimum temperature approach between steam and feedwater. What is its practical significance?

The correct answer is C: Determines the required surface area and operating cost of the exchanger. The pinch point represents the location where the minimum temperature difference exists between hot and cold fluids. A smaller pinch point requires larger heat transfer area (higher capital cost) but improves thermal effectiveness. The pinch point design directly impacts equipment sizing and economi

In a packed column used for gas absorption, the NTU (Number of Transfer Units) approach is preferred over HTU when:

The correct answer is C: The gas and liquid flow rates are both variable. NTU accounts for changing concentrations along the column height and is more versatile for varying flow rates, while HTU is better for constant flow conditions with linear equilibrium.

In the context of mass transfer, what does the Schmidt number (Sc) represent?

The correct answer is A: The ratio of kinematic viscosity to mass diffusivity. Schmidt number (Sc = ν/D_AB) represents the relative importance of momentum diffusion and mass diffusion in a fluid.

The relative roughness of a pipe is defined as:

The correct answer is B: Ratio of absolute roughness to pipe diameter. Relative roughness ε/D = (absolute roughness)/(pipe diameter). This dimensionless parameter determines flow behavior in the Moody chart for turbulent flow calculations.

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Chemical Engineering
Mass Transfer

Process design, thermodynamics, reactions

32 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 31–32 of 32

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

Q.31 Hard Mass Transfer

For turbulent flow in a pipe, the Colburn analogy for mass transfer is: j_D = (Sh)/(Re × Sc^(1/3)). Which correlation best estimates j_D for smooth pipes?

A j_D = 0.023 Re^(-0.2)

B j_D = 0.023 Re^(0.2)

C j_D = 0.037 Re^(-0.2)

D j_D = f/2 (where f is Fanning friction factor)

Correct Answer: A. j_D = 0.023 Re^(-0.2)

EXPLANATION

For smooth pipes in turbulent flow, j_D ≈ 0.023 Re^(-0.2), which is analogous to the Dittus-Boelert correlation for heat transfer with the Colburn j-factor approach.

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Q.32 Hard Mass Transfer

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?

A Gas phase controls the mass transfer

B Liquid phase controls the mass transfer

C Both phases equally resist mass transfer

D Equilibrium conversion is very low

Correct Answer: A. Gas phase controls the mass transfer

EXPLANATION

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.

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