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1255. When the ratio of the Grashoff number and to the square of Reynolds number is one, the dominant mechanism of heat transfer is

Free convection

Entry length problem in laminar forced conduction (developing thermal boundary layer)

Mixed convection (both free and forced)

Forced convection

✅ The correct answer is option C.

1258. When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as __________ boiling.

Pool

Nucleate

Transition

Film

✅ The correct answer is option D.

1261. The equivalent diameter for the annulus of a double pipe heat exchanger, whose inner pipe has fins on the outside is __________ compared to the same size pipes without fins.

Less

Same

Unpredictable

✅ The correct answer is option B.

1264. Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer co-efficient for the cooling water, whether on shell side or tube side is the same. The best arrangement is

Vertical heat exchanger with steam on tube side

Vertical heat exchanger with steam on shell side

Horizontal heat exchanger with steam on tube side

Horizontal heat exchanger with steam on shell side

✅ The correct answer is option B.

1267. Stefan-Boltzman law which describes the radiation heat transfer states that, it is proportional to (where, t = temperature in °C T = absolute temperature in ° K )

t⁴

T⁴

1/t⁴

1/T⁴

✅ The correct answer is option B.

1269. Overall heat transfer co-efficient of a particular tube is U₁. If the same tube with some dirt deposited on either side has coefficient U₂, then

U₁ = U₂

U₂ > U₁

U₁ > U₂

U₁ = dirt factor – U₂

✅ The correct answer is option A.

1271. Which of the following is correct?

Rate = Driving force x Resistance

Driving force = Rate x Resistance

Resistance = Driving force x Rate

Rate = Resistance/Driving force

✅ The correct answer is option B.

1273. Baffles in the shell side of a shell and tube heat exchanger

Increase the cross-section of the shell side liquid

Force the liquid to flow parallel to the bank

Increase the shell side heat transfer co-efficient

Decrease the shell side heat transfer co-efficient

✅ The correct answer is option C.

1275. For a laminar flow of fluid in a circular tube, ‘h₁’ is the convective heat transfer co-efficient at velocity ‘V₁’. If the velocity is reduced by half and assuming the fluid properties are constant, the new convective heat transfer co-efficient is

1.26 h₁

0.794 h₁

0.574 h₁

1.741 h₁

✅ The correct answer is option B.

1277. Which is the most suitable for the con-certration of highly concentrated solution?

Open pan evaporation

Long tube vertical evaporator

Agitated film evaporator

None of these

✅ The correct answer is option A.

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