Heat Transfer
JKSSB Junior Engineer (Mechanical) · Thermal Engineering and Refrigeration & Air-conditioning · 19 practice questions with answers and explanations: 6 Easy, 13 Medium, 0 Hard.
Sample questions
Sample Easy question 1
Which of these materials has the highest thermal conductivity?
- Air
- Wood
- Copper
- Glass wool
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Answer: C. Metals conduct heat much better than insulators.
Sample Easy question 2
Fins are added to a surface to:
- increase the heat transfer area
- reduce the weight only
- decrease the temperature difference
- stop convection
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Answer: A. More surface area means more heat is transferred.
Sample Easy question 3
The emissivity of a perfect black body is:
- 0.5
- 0
- 1
- infinite
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Answer: C. A black body is the best possible emitter.
Sample Medium question 4
For the same terminal temperatures, the log mean temperature difference of a counterflow heat exchanger is:
- greater than that of a parallel flow exchanger
- equal to it
- less than that of a parallel flow exchanger
- always zero
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Answer: A. Counterflow gives a larger LMTD and so needs less area.
Sample Medium question 5
The thermal resistance of a plane wall of thickness L, area A and thermal conductivity k is:
- k A / L
- L / (k A)
- k L / A
- A / (k L)
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Answer: B. Conduction resistance R = L/(kA).
Sample Medium question 6
For a composite wall of layers in series, the total thermal resistance is:
- the sum of the individual resistances
- the product of the resistances
- the largest resistance only
- the reciprocal of the sum of conductances
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Answer: A. Resistances in series add.