WTMA Heat Transfer and Conduction 4 — Questions and Answers
Question 1: A furnace pipe passes through a wall. To prevent the wall from overheating, you should install:
- A thicker metal sleeve
- A thermal insulating collar around the pipe (Correct answer)
- A copper heat sink on the pipe
- An aluminum foil wrap inside the wall
Correct answer: A thermal insulating collar around the pipe
An insulating collar reduces conduction from the hot pipe to the surrounding wall material.
Question 2: Which of the following best explains why a metal spoon left in hot soup becomes hot throughout its length?
- Convection currents in the spoon
- Radiation from the soup surface
- Conduction along the spoon from the hot end to the cool end (Correct answer)
- Evaporation from the soup
Correct answer: Conduction along the spoon from the hot end to the cool end
Heat conducts from the hot submerged end through the metal spoon to the cooler handle end.
Question 3: Two pipes carry the same hot fluid. Pipe A has twice the wall thickness of Pipe B, made of the same material. Which pipe loses more heat per hour through its walls?
- Pipe A, because it has more material to store heat
- Pipe B, because thinner walls offer less resistance to heat flow (Correct answer)
- Both lose heat at the same rate
- Pipe A, because thicker walls conduct more total heat
Correct answer: Pipe B, because thinner walls offer less resistance to heat flow
Thinner walls have lower thermal resistance, allowing more heat to conduct through per unit time.
Question 4: Why are the handles of cooking pots often made of plastic or wood rather than metal?
- Plastic and wood are stronger than metal
- Metal handles would corrode over heat
- Plastic and wood are poor heat conductors, keeping handles cool (Correct answer)
- Metal handles would melt
Correct answer: Plastic and wood are poor heat conductors, keeping handles cool
Non-metallic materials with low thermal conductivity prevent heat from conducting up to the handle where it would burn the hand.
Question 5: A heat exchanger transfers heat from hot exhaust gas to cold incoming air. The metal plates between them work because metal:
- Absorbs heat permanently
- Has high thermal conductivity, allowing rapid heat transfer through the plates (Correct answer)
- Radiates heat between the gas streams
- Prevents any heat from passing
Correct answer: Has high thermal conductivity, allowing rapid heat transfer through the plates
Metal's high thermal conductivity allows heat to quickly conduct from the hot side through the plate to the cold side.
Question 6: A welded steel joint is cooled rapidly with water immediately after welding. What thermal process is occurring at the joint surface?
- Radiation from the water
- Convection of heat from the steel into the moving water (Correct answer)
- Conduction with no fluid movement
- Sublimation of the steel
Correct answer: Convection of heat from the steel into the moving water
Moving water carries heat away from the steel surface through convection.
Question 7: If the thermal conductivity of a material is very high, that material makes a good:
- Insulator
- Reflector
- Conductor (Correct answer)
- Absorber of radiation
Correct answer: Conductor
High thermal conductivity directly defines a good thermal conductor—heat passes through it easily.
WTMA Heat Transfer and Conduction 4
A furnace pipe passes through a wall.
To prevent the wall from overheating, you should install: