21. With increase in temperature, the thermal conductivity of non-metallic amorphous solids
Decreases
Increases
Remains constant
First decreases upto certain temperature and then increases
✅ The correct answer is option B.
Heat Transfer MCQs
22. Mode of heat transfer involved in the cooling of air cooled internal combustion engine is
Conduction
Natural convection
Forced convection
None of these
✅ The correct answer is option B.
23. Baffles in the shell side of a shell and tube heat exchanger
Increase the cross-section of the shell side liquid
Force the liquid to flow parallel to the bank
Increase the shell side heat transfer co-efficient
Decrease the shell side heat transfer co-efficient
✅ The correct answer is option C.
24. Sensible heat absorbed by 1 lb of water when it is heated from 32 to 212°F may be around __________ BTU.
180
970
3.97
Data insufficient, can
✅ The correct answer is option A.
25. For a laminar flow of fluid in a circular tube, ‘h₁’ is the convective heat transfer co-efficient at velocity ‘V₁’. If the velocity is reduced by half and assuming the fluid properties are constant, the new convective heat transfer co-efficient is
1.26 h₁
0.794 h₁
0.574 h₁
1.741 h₁
✅ The correct answer is option B.
26. Resistance to heat flow by conduction is proportional to (where, t & ρ are thickness & density of the material respectively and A = area normal to the direction of heat flow. )
T
1/ρ
1/A
All of the above
✅ The correct answer is option D.
27. Which is the most suitable for the con-certration of highly concentrated solution?
Open pan evaporation
Long tube vertical evaporator
Agitated film evaporator
None of these
✅ The correct answer is option A.
28. At Pr > 1, conduction in an ordinary fluid flowing through a heated pipe is limited to the
Buffer zone
Turbulent core
Both A and B
Viscous sub-layer
✅ The correct answer is option D.
29. If h₁ = inner film co-efficient and /h₂ = outer film co-efficient, then the overall heat transfer co-efficient is
Always less than h₁
Always between h₁ and h₂
Always higher than h₂
Dependent on metal resistance
✅ The correct answer is option B.
30. When vaporisation takes place directly at the heating surface, it is called
Film boiling
Nucleate boiling
Vapour binding
None of these
✅ The correct answer is option B.