Same velocity profile or equal eddy diffusivities
Thermal or pressure mass diffusion
Viscous heating or chemical reaction
Both B and C
✅ The correct answer is option D.
Heat Transfer MCQs
The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50°C in industrial practice mainly to avoid
Its evaporation loss
Excessive corrosion
Uneconomic LMTD
Decrease in heat exchanger efficiency
✅ The correct answer is option B.
The actual temperature drop across the heating surface in an evaporator depends on the
Feed
Depth of liquid over heating surface
Pressure difference between steam chest and vapour space
All of the above
✅ The correct answer is option D.
The overall resistance for heat transfer through a series of flat resistance, is the __________ of the resistances.
Average
Geometric mean
Product
Sum
✅ The correct answer is option D.
Boiling of milk in an open vessel is an example of __________ boiling.
Film
Sub-cooled
Saturated nucleate
None of these
✅ The correct answer is option A.
A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the centre of the sphere reaches 350°K in 20 minutes, how long will it take for a 0.05 m radius steel sphere to reach the same temperature (at the centre) under identical conditions ? Assume that the conductive heat transfer co-efficient is infinitely large.
5 minutes
10 minutes
20 minutes
40 minutes
✅ The correct answer is option A.
In sub-cooled boiling,
Temperature of the heating surface is less than the boiling point of the liquid
Temperature of the heating surface is more than the boiling point of the liquid
Bubbles from heating surface are absorbed by the mass of the liquid
Very large vapour space is necessary
✅ The correct answer is option B.
In a cooling tower, water becomes cool by
Loosing sensible heat
Heat transfer to surroundings
Vaporisation due to heat loss to air
Loosing latent heat
✅ The correct answer is option A.
Duhring rule is important in solving problems on
Distillation
Crystallisation
Evaporation
Humidification
✅ The correct answer is option C.
Corrosiveness of steam condensate is due to the presence of
CO₂
Dissolved O₂
Both A & B
Neither A nor B
✅ The correct answer is option C.