Heat Transfer MCQs Archives

181. The actual temperature drop across the heating surface in an evaporator depends on the

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Depth of liquid over heating surface

Pressure difference between steam chest and vapour space

All of the above

✅ The correct answer is option D.

182. 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.

183. 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.

184. 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.

185. 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.

186. 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.

187. Duhring rule is important in solving problems on

Distillation

Crystallisation

Evaporation

Humidification

✅ The correct answer is option C.

188. 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.

189. __________ heat exchanger is used for chilling oil to be dewaxed.

U-tube

Double pipe

Fixed tube

Floating head

✅ The correct answer is option B.

190. The average heat transfer co-efficient over the entire length of the plate (ha) and the local heat transfer co-efficient (hL), in case of heat transfer over a flat plate in lminar zone is related as

Ha = 0.8hL

Ha = 2hL

Ha = hL

Ha= 5hL

✅ The correct answer is option B.