Heat Transfer

Question: Kirchoff’s law is applicable to
[A].

monochromatic radiation only

[B].

total radiation only

[C].

both (a) and (b)

[D].

only volumes and not to surfaces

Answer: Option C

Explanation:

No answer description available for this question.

Question: As per Kirchoffs law, the ratio of the total radiating power to the absorptivity of a body depends on the
[A].

temperature of the body only.

[B].

wavelength of monochromatic radiation.

[C].

both (a) and (b).

[D].

nature of material of body.

Answer: Option A

Explanation:

No answer description available for this question.

Question: Nucleate boiling is promoted
[A].

on polished surfaces

[B].

on rough surfaces

[C].

in the absence of agitation

[D].

none of these

Answer: Option B

Explanation:

No answer description available for this question.

Question: Heat flux increases with temperature drop beyond the Leiden frost point in the plot of heat flux vs. temperature drop for a boiling liquid, because
[A].

convection becomes important

[B].

conduction becomes important

[C].

radiation becomes important

[D].

sub-cooled boiling occurs

Answer: Option C

Explanation:

No answer description available for this question.

Question: In sub-cooled boiling,
[A].

temperature of the heating surface is less than the boiling point of the liquid.

[B].

temperature of the heating surface is more than the boiling point of the liquid.

[C].

bubbles from heating surface are absorbed by the mass of the liquid.

[D].

very large vapour space is necessary.

Answer: Option B

Explanation:

No answer description available for this question.

Question: Film boiling is usually not desired in commercial equipments, because
[A].

the heat transfer rate is low in view of the large temperature drop.

[B].

it is difficult to maintain.

[C].

it is not economic.

[D].

none of these.

Answer: Option A

Explanation:

No answer description available for this question.

Question: Dropwise condensation occurs on __________ surfaces.
[A].

clean and dirt free

[B].

smooth clean

[C].

contaminated cooling

[D].

polished

Answer: Option C

Explanation:

No answer description available for this question.

Question: All analogy equations connecting friction factor and heat transfer co-efficient apply only to
[A].

wall or skin friction

[B].

form friction

[C].

both (a) and (b)

[D].

turbulent flow

Answer: Option A

Explanation:

No answer description available for this question.

Question: If average heat transfer co-efficient is ha and the local coefficient at the end of the plate is hl then in case of heat transfer to a fluid flowing over a flat plate, heated over its entire length
[A].

ha = hl

[B].

ha = 2hl

[C].

ha = 0.5 hl

[D].

ha = 0.75 hl

Answer: Option B

Explanation:

No answer description available for this question.

Question: For a liquid in laminar flow through a very long tube, when the exit fluid temperature approaches the wall temperature, the equation to be used is
[A].

Nu = 0.023 Re0.8 . Pr0.4

[B].

Nu = Gz

[C].

Nu = Gz

[D].

Nu = 2Gz0.5

Answer: Option C

Explanation:

No answer description available for this question.