At high fluid velocity
At low velocity
When fluid flows past a smooth surface
None of these
✅ The correct answer is option A.
Heat Transfer MCQs
112. With increase in temperature, the thermal conductivity of fresh lubricating oil
Increases
Decreases
Remains unchanged
May increase or decrease; depends on its composition
✅ The correct answer is option B.
113. Thermal conductivity of a conducting solid material depends upon its
Temperature
Porosity
Both A & B
Neither A nor B
✅ The correct answer is option C.
114. Dropwise condensation of steam on cooling surface is promoted
An oily surface
When both the steam and the tube are clean
Only in presence of air
None of these
✅ The correct answer is option A.
115. Prandtl number for most of dry gases is about
0.001
0.72
70
150
✅ The correct answer is option B.
116. The number of kg vaporised per kg of steam fed to the evaporator is defined as
Capacity
Rate of evaporation
Economy
Rate of vaporisation
✅ The correct answer is option C.
117. Mechanical recompression evaporation is used in the production of
Alcohol
Distilled water
Salt
Fruits jam
✅ The correct answer is option B.
118. Heat flux, as defined in heat flow is analogous to __________ in electricity flow.
Current
Voltage
Resistance
None of these
✅ The correct answer is option A.
119. With increase in temperature, the thermal conductivity of steel
Increases
Decreases
Remains unchanged
Increases exponentially
✅ The correct answer is option B.
120. A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest ?
Cube
Plate
Sphere
All of the above
✅ The correct answer is option C.