ME 323

What are the correct heat transfer mechanisms for the identified systems?

• Q1: Convection, radiation

  Q2: Radiation

  Q3: Convection

• Q1: Conduction

  Q2: Radiation

  Q3: Convection, radiation

• Q1: Conduction

  Q2: Radiation, conduction

  Q3: Convection

• Q1: Conduction

  Q2: Radiation

  Q3: Convection

On a hot summer day, a student turns his fan on when he

leaves his room in the morning. When he returns in the evening,

will his room be warmer or cooler than the neighboring rooms? (Assume all the doors and windows are kept closed.)

• Warmer

• Cooler

• Not different from them

Which is a better heat conductor?

• Steel

• Copper

• Diamond

• Aluminum

Consider a hot dog being cooked in boiling water in a

pan. Would the heat transfer to the hot dog be steady or

transient?

• Steady

• Transient

Radiation heat transfer increases, ...

• when the temperature gradient decreases between the bodies.

• when the thermal conductivity of the body increases.

• when the heat transfer surface area decreases.

• when the emissivity of the surface increases.

Two finned surfaces with long fins are identical,

except that the convection heat transfer coefficient for the first

the finned surface is twice that of the second one. What statement

below is accurate for the efficiency and effectiveness of the

Is the first finned surface relative to the second one?

• Higher efficiency and higher effectiveness

• Higher efficiency but lower effectiveness

• Lower efficiency but higher effectiveness

• Lower efficiency and lower effectiveness

• Equal efficiency and equal effectiveness

Which one is the equivalent thermal resistance for the thermal circuit shown below?

• 
• 
• 
• 
• 

Consider two metal plates pressed against each other. Other things being equal, which of the measures below will cause the thermal contact resistance to increase?

• Pressing the plates against each other with a greater force

• Filling the gap with a conducting fluid

• Cleaning the surfaces to make them shinier

• Coating the contact surfaces with a thin layer of soft metal such as tin

• Using softer metals

Which wall has the greatest thermal resistance where k is the thermal conductivity of the wall, L is the thickness of the wall, A is the surface area of the wall?

• R1

  k = 20 W/mK

  A = 0.5 m^2

  L = 0.1 m

• R2

  k = 15 W/mK

  A = 5 m^2

  L = 0.1 m

• R3

  k = 10 W/mK

  A = 0.5 m^2

  L = 0.01 m

• R4

  k = 2.5 W/mK

  A = 2 m^2

  L = 0.02 m