In a once-through steam generator (OTSG) for heat recovery, the effectiveness-NTU relation for counterflow is ε = 1 - exp(-NTU(1-C_r))/(1-C_r·exp(-NTU(1-C_r))) where C_r = C_min/C_max. When C_r = 1, this simplifies to:

The correct answer is A: ε = NTU/(1 + NTU). For C_r = 1 (equal capacity rates), counterflow relation simplifies to ε = NTU/(1 + NTU), same as parallel flow.

For a pseudosteady-state diffusion with heterogeneous reaction, the effectiveness factor η accounts for:

The correct answer is A: The reduction in reaction rate due to limited diffusion to active sites. η = (actual reaction rate)/(rate if all surface at bulk concentration). Important in catalytic reactors where diffusion and reaction compete.

Which of the following is NOT an extensive property?

The correct answer is B: Temperature. Temperature is an intensive property as it does not depend on the quantity of substance. Volume, mass, and internal energy are extensive properties that depend on the amount of material.

In a cocurrent absorption tower where gas and liquid flow in the same direction, compared to counter-current operation:

The correct answer is A: Cocurrent towers require larger height for same separation. Counter-current flow provides greater concentration differences throughout the tower (larger average driving force), requiring less height and contact time compared to cocurrent operation for equivalent separation.

In a countercurrent absorption column, if the gas-phase mass transfer coefficient is k_G = 0.05 kmol/(m²·s·atm), the interfacial area 'a' = 200 m²/m³, and column cross-section = 5 m², the volumetric overall mass transfer coefficient is:

The correct answer is B: 50 kmol/(s·atm). Overall volumetric mass transfer = k_G × a × Volume = 0.05 × 200 × (5 × height). For unit height, K_G·a·V = 0.05 × 200 × 5 = 50 kmol/(s·atm).

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Chemical Engineering
Fluid Mechanics

Process design, thermodynamics, reactions

15 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–15 of 15

Topics in Chemical Engineering

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

Q.11 Hard Fluid Mechanics

A gas flows through a convergent nozzle. At what condition does maximum mass flow rate occur in the nozzle exit?

A When subsonic flow exists throughout

B When Mach number at exit = 1.0 (sonic condition)

C When pressure ratio equals 1.5

D When temperature is maximum

Correct Answer: B. When Mach number at exit = 1.0 (sonic condition)

EXPLANATION

For convergent nozzles, mass flow becomes independent of downstream pressure when throat reaches sonic conditions (M = 1)

Test

Q.12 Hard Fluid Mechanics

Which of the following best describes the boundary layer separation phenomenon?

A Occurs when pressure increases in the direction of flow

B Results from adverse pressure gradient causing flow reversal

C Always occurs after the maximum thickness point

D Is independent of Reynolds number

Correct Answer: B. Results from adverse pressure gradient causing flow reversal

EXPLANATION

Boundary layer separation occurs when an adverse (positive) pressure gradient opposes the flow, causing the flow to reverse near the wall and separate from the surface.

Test

Q.13 Hard Fluid Mechanics

A pipeline carries water at 20°C. When the flow velocity increases from 1 m/s to 3 m/s in a straight horizontal pipe of constant diameter, the friction factor:

A Increases by factor of 3

B Decreases

C Remains essentially constant

D Increases by factor of 9

Correct Answer: C. Remains essentially constant

EXPLANATION

For a given pipe with constant diameter and same fluid (constant Re behavior), the friction factor depends on Re and relative roughness. For geometrically similar conditions, f remains relatively constant in turbulent flow.

Test

Q.14 Hard Fluid Mechanics

For compressible flow through a converging-diverging nozzle (de Laval nozzle), the throat conditions occur where:

A Pressure is maximum

B Mach number equals 1

C Velocity is minimum

D Temperature is maximum

Correct Answer: B. Mach number equals 1

EXPLANATION

In a converging-diverging nozzle for supersonic flow, sonic conditions (M=1) occur at the throat. Beyond the throat, the flow accelerates to supersonic speeds.

Test

Q.15 Hard Fluid Mechanics

For a given pipe and fluid, if the flow velocity doubles, the pressure drop in turbulent flow will approximately:

A Double

B Quadruple

C Increase 1.8 to 2 times

D Remain same

Correct Answer: C. Increase 1.8 to 2 times

EXPLANATION

In turbulent flow, ΔP ∝ f × V^m where m is between 1.8-2 depending on friction factor variation. Not exactly V² due to changing friction factor with Re.

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