What is the fundamental driving force for all heat transfer processes?

Temperature difference (ΔT) between two regions or systems.

True or False: Conduction requires bulk motion of material for heat transfer.

False. Conduction occurs through molecular-level energy exchange without bulk motion.

The thermal conductivity of aluminum is 237 W/m·K. What does this value represent?

Material's ability to conduct heat through its structure per unit temperature gradient.

For a pipe with inner radius 2 cm and outer radius 4 cm, what is ln(ro/ri)?

Ln(4/2) = ln(2) = 0.693

Which heat exchanger configuration provides the highest effectiveness for given conditions?
A) Parallel flow
B) Counterflow
C) Crossflow
D) Mixed flow

B) Counterflow

The Reynolds number for pipe flow transitions from laminar to turbulent at Re = _____.

2300

What happens to heat loss when insulation thickness exceeds the critical radius?

Heat loss decreases as insulation thickness increases beyond critical radius.

True or False: The Nusselt number represents dimensionless heat transfer coefficient.

True. Nu = hD/k relates convective to conductive heat transfer.

Calculate thermal resistance for 5 cm thick wall, k=2 W/m·K, area=10 m².

R = L/(kA) = 0.05/(2×10) = 0.0025 K/W

Which dimensionless number determines natural convection strength?
A) Reynolds
B) Prandtl
C) Grashof
D) Weber

C) Grashof

Why is counterflow more efficient than parallel flow in heat exchangers?

Maintains more uniform temperature difference along entire heat exchanger length.

The lumped capacitance method applies when Biot number is less than _____.

0.1

True or False: Adding insulation always reduces heat transfer from pipes.

False. For small pipes, adding insulation can increase heat transfer initially.

What does effectiveness equal to 0.8 mean in heat exchanger performance?

Actual heat transfer is 80% of maximum theoretically possible heat transfer.

Scenario: Steam at 150°C flows through uninsulated pipe in 20°C air. Name three heat transfer modes occurring.

Conduction through pipe wall, convection to air, radiation to surroundings.

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

3.66

Which parameter becomes zero when fluid undergoes phase change?
A) Heat capacity rate
B) Capacity ratio
C) NTU
D) Effectiveness

B) Capacity ratio

True or False: LMTD method requires known inlet and outlet temperatures.

True. LMTD method needs all four terminal temperatures to calculate.

Why does fin effectiveness decrease as fin thermal conductivity decreases?

Lower conductivity reduces fin's ability to transfer heat from base.

Calculate critical radius for insulation with k=0.04 W/m·K and ho=10 W/m²·K.

Rcr = k/ho = 0.04/10 = 0.004 m = 4 mm

True or False: Turbulent flow always has higher heat transfer than laminar flow.

True. Turbulent mixing enhances heat transfer compared to laminar flow.

What does NTU represent in effectiveness-NTU method?

Number of Transfer Units, measuring heat exchanger thermal size relative to capacity.

For parallel thermal resistances R₁ and R₂, total resistance equals _____.

1/Rtotal = 1/R₁ + 1/R₂