The effectiveness-NTU (Number of Transfer Units) method is preferred over LMTD method when designing heat exchangers because:

The correct answer is B: LMTD method cannot handle cases where outlet temperatures are unknown (design problems). In heat exchanger design, outlet temperatures are unknown, making the LMTD method iterative and cumbersome. The NTU method (ε-NTU) directly uses inlet temperatures and known parameters to find the outlet temperatures without iteration, making it ideal for design problems.

In a jacketed CSTR for an endothermic reaction, increasing the heat transfer area per unit volume of reactor primarily affects which parameter?

The correct answer is C: Reaction rate and operating temperature stability. Increased heat transfer area improves heat supply rate for endothermic reactions, allowing higher operating temperatures with better temperature control and stability.

In compressible flow through a nozzle, sonic or critical conditions occur when Mach number equals:

The correct answer is B: 1.0. Critical or sonic conditions occur at Mach number = 1.0, where velocity equals the speed of sound in the fluid.

A fluid flows through a sudden expansion from pipe diameter D₁ = 0.05 m to D₂ = 0.1 m with velocity V₁ = 4 m/s. Calculate the pressure recovery coefficient (Cp) for the expansion.

The correct answer is B: 0.56. For sudden expansion, Cp = 1 - (A₁/A₂)² = 1 - (D₁/D₂)⁴ = 1 - (0.05/0.1)⁴ = 0.9375, but accounting for losses, recovery coefficient ≈ 0.56

Which dimensionless number is used to characterize the ratio of inertial forces to viscous forces in fluid flow?

The correct answer is B: Reynolds number. Reynolds number (Re = ρVD/μ) represents the ratio of inertial to viscous forces and determines the flow regime (laminar, transitional, or turbulent).

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Chemical Engineering

Process design, thermodynamics, reactions

117 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 51–60 of 117

Topics in Chemical Engineering

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

Q.51 Hard Fluid Mechanics

In a converging-diverging nozzle, if pressure increases in the diverging section, what type of flow pattern occurs?

A Supersonic to subsonic transition with shock

B Continued acceleration

C Constant velocity

D Uniform expansion

Correct Answer: A. Supersonic to subsonic transition with shock

EXPLANATION

Pressure increase in diverging section indicates deceleration, which occurs when supersonic flow transitions to subsonic through a normal shock wave.

Test

Q.52 Hard Fluid Mechanics

In pipe flow with fittings, which fitting typically causes the highest pressure loss coefficient (K)?

A 45° elbow

B 90° elbow

C Gate valve (fully open)

D Sudden contraction

Correct Answer: D. Sudden contraction

EXPLANATION

Sudden contraction typically has K ≈ 0.5, while 90° elbow has K ≈ 0.9, but sudden expansion losses are highest at K > 1.0 for significant diameter changes

Test

Q.53 Hard Fluid Mechanics

In boundary layer theory, the displacement thickness (δ*) represents which physical concept?

A The actual thickness of viscous region

B The distance by which the streamline is displaced due to the formation of boundary layer

C The thickness where velocity equals 99% of free stream velocity

D The region where shear stress becomes zero

Correct Answer: B. The distance by which the streamline is displaced due to the formation of boundary layer

EXPLANATION

Displacement thickness is the distance the external streamline is displaced due to the reduction in flow velocity within the boundary layer

Test

Q.54 Hard Fluid Mechanics

The Moody diagram is used to determine friction factor in pipes. For which flow regime is the Darcy friction factor independent of Reynolds number?

A Laminar flow

B Transition zone

C Fully developed turbulent flow in rough pipes

D Creeping flow

Correct Answer: C. Fully developed turbulent flow in rough pipes

EXPLANATION

In fully turbulent flow in rough pipes, friction factor depends only on relative roughness, not Reynolds number

Test

Q.55 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.56 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.57 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.58 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.59 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.

Test

Q.60 Hard Heat Transfer

For turbulent flow over a flat plate, the local Nusselt number varies with distance x according to which relationship?

A Nu_x ∝ x^0.5

B Nu_x ∝ x^(-0.5)

C Nu_x ∝ x^(-0.1)

D Nu_x is independent of x

Correct Answer: C. Nu_x ∝ x^(-0.1)

EXPLANATION

For turbulent boundary layer on flat plate: Nu_x = 0.0296·Re_x^0.8·Pr^(1/3), and since Re_x ∝ x, Nu_x increases with x^0.8. However, local values decrease along length in terms of difference from correlation; relationship is complex.

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