151. Which of the following has maximum thermal conductivity?
Iron
Coal
Nitrogen
Tar
✅ The correct answer is option A.
Heat Transfer MCQs
153. For gases, the thermal conductivity increases with temperature rise. For liquids, with increase in concentration, its thermal conductivity generally
Decreases
Increases
Remains unchanged
Increases exponentially
✅ The correct answer is option A.
154. If the thermal conductivity of a wall material is independent of temperature, the steady state temperature distribution in the very large thin plane wall having steady, uniform surface temperature follows __________ law.
Hyperbolic
Parabolic
Linear
Logarithmic
✅ The correct answer is option C.
155. Which of the following is the most widely used heat insulating material for pipelines carrying steam?
Tar dolomite bricks followed by asbestos
Fireclay refractory followed by aluminium sheet
Cotton followed by aluminium foil
85% magnesia cement and glass wool
✅ The correct answer is option D.
156. Planck’s distribution law is valid for __________ bodies.
Black
White
Coloured
All of the above
✅ The correct answer is option C.
157. In a co-current double pipe heat exchanger used for condensing saturated steam over the inner tube, if the entrance and exit conditions of the coolant are interchanged, then the rate of condensation will
Increase
Decrease
Remain unchanged
Either increase or decrease; depends on the coolant flow rate
✅ The correct answer is option C.
158. With increase in porosity, the thermal conductivity of a solid substance
Increases
Decreases
Remains unchanged
May increase or decrease; depends on the solid
✅ The correct answer is option B.
159. Unsteady state heat conduction occurs, when
Temperature distribution is independent of time
Temperature distribution is dependent on time
Heat flows in one direction only
Three dimensional heat flow is concerned
✅ The correct answer is option B.
160. The thermal boundary layer at NPr > 1
Is thicker than hydrodynamic boundary layer
Is thinner than hydrodynamic boundary layer
And the hydrodynamic boundary layer are identical
Disappears
✅ The correct answer is option B.