What does LMTD stand for in heat exchanger analysis?

Log Mean Temperature Difference

True or False: Counter-flow heat exchangers are more thermodynamically efficient than parallel-flow.

True. Counter-flow configuration provides the highest effectiveness for given NTU and Cᵣ.

In the effectiveness-NTU method, NTU = _____/C_min

UA

Which heat exchanger type has the highest surface area-to-volume ratio?
A) Shell-and-tube
B) Double-pipe
C) Compact
D) Cross-flow

C) Compact

What causes fouling in heat exchangers?

Scale deposition, corrosion, biological growth, or particulate accumulation on surfaces.

For parallel-flow arrangement, both fluids enter at the _____ end.

Same

True or False: When one fluid undergoes phase change, Cᵣ approaches zero.

True. The fluid at constant temperature has infinite heat capacity rate.

What is the formula for overall heat transfer coefficient through a flat wall?

1/U = 1/hᵢ + t/k + 1/hₒ

In a 1-2 shell-and-tube heat exchanger, how many shell passes are there?
A) 1
B) 2
C) 3
D) 4

A) 1

What does effectiveness (ε) represent in heat exchanger analysis?

Ratio of actual heat transfer to maximum possible heat transfer.

For turbulent flow in tubes, which correlation is commonly used: Nu = 0.023 Re^0.8 Pr^n?

Dittus-Boelter equation

True or False: Compact heat exchangers have area density greater than 700 m²/m³.

True. This is the defining criterion for compact heat exchangers.

What happens to LMTD when a correction factor F is applied?

LMTD is multiplied by F for multi-pass and cross-flow configurations.

In cross-flow heat exchangers, fluids flow _____ to each other.

Perpendicular

For counter-flow with Cᵣ = 1, effectiveness equals _____/(1 + NTU).

NTU

Which method is preferred when outlet temperatures are unknown?
A) LMTD
B) Effectiveness-NTU
C) Energy balance
D) Fouling analysis

B) Effectiveness-NTU

True or False: Shell-and-tube heat exchangers allow various pass configurations.

True. They can have multiple tube passes and shell passes.

What does Cᵣ represent in effectiveness-NTU analysis?

Heat capacity ratio (Cₘᵢₙ/Cₘₐₓ)

For laminar flow in circular tubes with constant wall temperature, Nu = _____.

3.66

When is LMTD method most appropriate to use?

When inlet and outlet temperatures are known (rating problems).

What parameter indicates the size of a heat exchanger in NTU method?

NTU (Number of Transfer Units)

True or False: All flow configurations have the same effectiveness when Cᵣ = 0.

True. Effectiveness equals 1 - exp(-NTU) for phase change applications.

In pressure drop calculations, what does the friction factor f represent?

Darcy friction factor from Moody chart or Colebrook equation.

Which heat exchanger configuration is most common in industrial applications?
A) Double-pipe
B) Shell-and-tube
C) Plate
D) Regenerative

B) Shell-and-tube

For constant heat flux in circular tubes, Nu = _____.

4.36

What does the P parameter represent in LMTD correction factor charts?

P = (Tc,out - Tc,in)/(Th,in - Tc,in)

True or False: Fouling resistance decreases overall heat transfer coefficient.

True. Fouling adds thermal resistance, reducing U.

In the Dittus-Boelter equation, what value of n is used for heating?

0.4

What is the standard tube length range for shell-and-tube heat exchangers?
A) 4-8 ft
B) 8-20 ft
C) 20-30 ft
D) 30-40 ft

B) 8-20 ft

For condensation on horizontal tubes, which factor appears in the denominator: D or L?

D (tube diameter)

What does C represent in heat capacity rate calculations?

C = ṁcₚ (mass flow rate times specific heat)

True or False: Baffle spacing in shell-and-tube exchangers is typically 20-50% cut.

True. This is the standard range for segmental baffle design.

For cross-flow with both fluids unmixed, effectiveness involves which exponential term: exp[-Cᵣ·NTU^0.78]?

This term appears in the complex effectiveness correlation for unmixed cross-flow.