101. What is the emissivity of a black body?
1
0
0.9
0.5
✅ The correct answer is option A.
Heat Transfer MCQs
102. Mode of heat transfer in which the fluid moves under the influence of changes in fluid pressure produced by external work is called
Radiation
Natural convection
Forced convection
Conduction
✅ The correct answer is option C.
103. What is the steam economy in case of a single effect evaporator system?
1
>1
< 1
0.1
✅ The correct answer is option C.
104. Fourier’s law of heat conduction applies to __________ surfaces.
Isothermal
Non-isothermal
Both A and B
Neither A and B
✅ The correct answer is option C.
105. In case of heat transfer by conduction in a hollow cylinder, __________ mean area is used to calculate the heat transfer rate.
Geometric
Arithmetic
Logarithmic
Either A, B or C
✅ The correct answer is option C.
106. In case of a multipass shell and tube heat exchanger, providing a baffle on the shell side __________ the heat transfer rate.
Increases
Decreases
Does not affect
May increase or decrease, depends on the type of baffle
✅ The correct answer is option A.
107. A composite wall consists of two plates A and B placed in series normal to the flow of heat. The thermal conductivities are kA and kB and the specific heat capacities are CPA and CPB for plates A and B respectively. Plate B has twice the thickness of plate A. At steady state, the temperature difference across plate A is greater than that across plate B, when
CPA > CPB
CPA < CPB
KA < 0.5kB
KA>2 kB
✅ The correct answer is option C.
108. The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as
(ΔT)1/4
(ΔT)1/2
(ΔT)5/4
(ΔT)3/4
✅ The correct answer is option D.
109. The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U0 = 400 W/m².K. The fouling factor after one year of operation is found to be hd0 = 2000 W/m².K. The overall heat transfer co-efficient at this time is
1200W/m².K
894W/m².K
333W/m².K
287 W/m².K
✅ The correct answer is option C.
110. For concentrating an aqueous solution of a material like anhydrous Na₂SO₄, whose solubility decreases with rise in temperature, the most suitable evaporator is a __________ evaporator.
High pressure
Vacuum
Backward feed
None of these
✅ The correct answer is option B.