The eddy diffusivity (ε_D) in turbulent flow represents contribution of _____ to overall mass transfer.

The correct answer is B: Turbulent eddies and mixing. Eddy diffusivity (ε_D) accounts for the enhanced mass transfer due to turbulent mixing and eddy formation. Total diffusivity = D_AB + ε_D in turbulent regions.

In radiation view factor calculations, the reciprocity relation F₁₂·A₁ = F₂₁·A₂ ensures:

The correct answer is A: Energy conservation in radiation exchange. Reciprocity relation ensures energy conservation: heat leaving surface 1 striking surface 2 equals heat leaving 2 striking 1 on reciprocal basis.

For an open channel with trapezoidal cross-section, which parameter is used to determine the wetted perimeter?

The correct answer is B: Width, depth, and side slope. Wetted perimeter = b + 2d√(1+z²), where b is width, d is depth, and z is side slope. All three parameters are essential.

For a first-order consecutive reaction A → B → C where k₁ = 0.1 min⁻¹ and k₂ = 0.05 min⁻¹, the maximum concentration of intermediate B occurs at approximately:

The correct answer is C: t = 13.86 minutes. For consecutive reactions, [B]max occurs at t_max = ln(k₁/k₂)/(k₁-k₂) = ln(2)/0.05 = 13.86 minutes

What is the order of reaction if the rate law is: rate = k[A]^(1/2)[B]?

The correct answer is B: 1.5-order. Order = sum of exponents = 1/2 + 1 = 1.5 (fractional order, common in enzyme kinetics)

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Chemical Engineering

Process design, thermodynamics, reactions

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Difficulty: All Easy Medium Hard 221–230 of 247

Topics in Chemical Engineering

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

Q.221 Medium Mass Transfer

In evaporative cooling, the effectiveness (ε) is defined as:

A Ratio of actual temperature drop to maximum possible drop (wet bulb approach)

B Ratio of mass flow rate of water evaporated to air mass flow

C Percentage of heat transferred to total sensible heat

D Ratio of outlet to inlet air humidity ratio

Correct Answer: A. Ratio of actual temperature drop to maximum possible drop (wet bulb approach)

EXPLANATION

ε = (t_in - t_out)/(t_in - t_wb). Higher effectiveness indicates better utilization of air capacity, crucial for cooling tower design.

Test

Q.222 Medium Mass Transfer

The concept of 'equivalent theoretical stages' in absorption is based on:

A Comparing actual performance with theoretical maximum from equilibrium stages

B Counting the number of stages physically present

C Calculating residence time in the column

D Measuring pressure drop across stages

Correct Answer: A. Comparing actual performance with theoretical maximum from equilibrium stages

EXPLANATION

Used to compare different types of contactors. Actual stages divided by Murphree efficiency gives equivalent theoretical stages needed.

Test

Q.223 Medium Mass Transfer

For gas absorption in a plate column, the gas-phase mass transfer coefficient increases with:

A Higher gas velocity and lower pressure

B Lower gas velocity and higher pressure

C Decreased column diameter

D Increased liquid viscosity

Correct Answer: A. Higher gas velocity and lower pressure

EXPLANATION

Higher velocity increases turbulence (higher k); lower pressure increases diffusivity D. Both increase Sh = kL/D.

Test

Q.224 Medium Mass Transfer

In distillation, the Murphree plate efficiency is defined as the ratio of:

A Actual separation achieved to theoretical maximum separation possible

B Vapor flow rate to liquid flow rate

C Stage temperature to feed temperature

D Condenser duty to reboiler duty

Correct Answer: A. Actual separation achieved to theoretical maximum separation possible

EXPLANATION

E_mv = (y_n - y_(n-1))/(y*_n - y_(n-1)), where y* is equilibrium vapor composition. Accounts for non-equilibrium stage behavior.

Test

Q.225 Medium Mass Transfer

For simultaneous heat and mass transfer in a cooling tower, the Lewis number (Le = α/D) typically has a value of:

A Approximately 1 for air-water system

B Always greater than 1

C Dependent only on temperature

D Independent of substance pair

Correct Answer: A. Approximately 1 for air-water system

EXPLANATION

For air-water system: Le = α/D ≈ 0.8-1.0. This means heat and mass transfer coefficients are comparable, important for cooling tower design.

Test

Q.226 Medium Mass Transfer

The penetration theory for mass transfer assumes that:

A Eddies expose fresh bulk fluid to the interface for short contact times

B A stagnant film exists at the interface indefinitely

C Mass transfer is independent of time

D Turbulence is completely absent

Correct Answer: A. Eddies expose fresh bulk fluid to the interface for short contact times

EXPLANATION

Penetration theory (Higbie) assumes eddies contact interface, remain for time θ, then submerge. More realistic than film theory for turbulent systems.

Test

Q.227 Medium Mass Transfer

In a continuous contacting device, the operating line is obtained from which fundamental principle?

A Material balance equation

B Energy balance

C Equilibrium relation

D Rate equation

Correct Answer: A. Material balance equation

EXPLANATION

Operating line represents all possible compositions entering and leaving the device based on material balance: Y₁ - Y₂ = (L/V)(X₁ - X₂)

Test

Q.228 Medium Mass Transfer

The Sherwood number (Sh) in mass transfer is analogous to which number in heat transfer?

A Nusselt number (Nu)

B Rayleigh number (Ra)

C Grashof number (Gr)

D Fourier number (Fo)

Correct Answer: A. Nusselt number (Nu)

EXPLANATION

Sh = kL·L/D is analogous to Nu = h·L/k. Both represent dimensionless transfer coefficients for mass and heat respectively.

Test

Q.229 Medium Mass Transfer

In a packed column absorption operation, the overall mass transfer coefficient KG is related to individual phase coefficients by:

A 1/KG = 1/kG + (m/kL)

B KG = kG + kL

C 1/KG = 1/kL + 1/kG

D KG = m·kG·kL

Correct Answer: A. 1/KG = 1/kG + (m/kL)

EXPLANATION

For gas-phase controlling resistance: 1/KG = 1/kG + (m/kL), where m is Henry's Law constant and accounts for equilibrium relationship.

Test

Q.230 Medium Mass Transfer

In the design of a sieve tray distillation column, the mass transfer efficiency (Murphree efficiency) accounts for:

A The deviation from equilibrium due to finite mass transfer rate

B The pressure drop across the tray

C The temperature gradient in the column

D The liquid holdup on the tray

Correct Answer: A. The deviation from equilibrium due to finite mass transfer rate

EXPLANATION

Murphree efficiency (E_M) reflects that equilibrium is not achieved on real trays due to limited contact time and finite mass transfer rates in the actual column.

Test

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