1534. In which mode of heat transfer, the Biot number is important?
Transient heat conduction
Natural convection
Forced convection
Radiation
✅ The correct answer is option A.
1536. A black body when hot, emits heat radiation of __________ wavelengths.
Small
Large
All
One fixed
✅ The correct answer is option C.
1538. A dephlegmator is a
Total condenser
Vacuum evaporator
Partial condenser
Double pipe heat exchanger
✅ The correct answer is option C.
1540. A composite flat wall of a furnace is made of two materials ‘A’ and ‘B’. The thermal conductivity of ‘A’ is twice of that of material ‘B’, while the thickness of layer of ‘A’ is half that of B. If the temperature at the two sides of the wall are 400 and 1200°K, then the temperature drop (in °K) across the layer of material ‘A’ is
125
133
150
160
✅ The correct answer is option D.
1542. The purpose of providing a ‘catchall’ in the vapor line of an evaporator is to
Create vacuum
Regulate the vapor flow
Vent the non-condensible gases
Arrest the entrained liquid
✅ The correct answer is option D.
1544. Minimum recommended baffle spacing in a shell and tube heat exchanger is about (where, D = shell diameter)
0.2 D
0.5 D
0.66 D
0.80 D
✅ The correct answer is option A.
1546. Which of the following is not used as a medium for high temperature heating?
Dowtherm
Mercury
Liquid metal (e.g. molten sodium)
Fused salts (e.g., an eutectic mixture of 53% KNO₃, 40% NaNO₂and 7% NaNO₃)
✅ The correct answer is option B.
1548. Harmonic mean temperature difference is given by
√(ΔT₁ . ΔT₂)
2.(ΔT₁ . ΔT₂)/(ΔT₁ + ΔT₂)
2.(ΔT₁ . ΔT₂)(ΔT₁ – ΔT₂)
(ΔT₁ – ΔT₂)/(ΔT₁ . ΔT₂)
✅ The correct answer is option B.
1550. The actual temperature drop across the heating surface of an evaporator depends on the
Liquid depth over the heating surface
Solution being evaporated
Pressure difference between the steam chest and the vapor space above the boiling liquid
All of the above
✅ The correct answer is option D.
1553. 1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, using immersed coils carrying condensing steam at 150°C. The area of the steam coils is 1.2 m² and the overall heat transfer co-efficient to the liquid is 1500 W/m².°C. Assuming negligible heat loss to the surrounding and specific heat capacity of the liquid to be 4 kJ/kg.°C, the time taken for the liquid to reach desired temperature will be
15 min
22 min
44 min
51 min
✅ The correct answer is option D.