Heat Transfer

Question: A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be
[A].

greater than that for uninsulated steam pipe.

[B].

less than that of the uninsulated steam pipe.

[C].

equal to that of the uninsulated steam pipe.

[D].

less than the steam pipe with 5 cms insulation.

Answer: Option B

Explanation:

No answer description available for this question.

Question: If the baffle spacing in a shell and tube heat exchanger increases, then the Reynolds number of the shell side fluid
[A].

remains unchanged.

[B].

increases.

[C].

increases or decreases depending on number of shell passes.

[D].

decreases.

Answer: Option D

Explanation:

No answer description available for this question.

Question: In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m2.s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m2/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is
[A].

2000

[B].

4000

[C].

5000

[D].

6000

Answer: Option C

Explanation:

No answer description available for this question.

Question: As the difference between the wall temperature and bulk temperature increases, the boiling heat transfer co-efficient
[A].

continues to increase.

[B].

continues to decrease.

[C].

goes through a minimum.

[D].

goes through a maximum.

Answer: Option C

Explanation:

No answer description available for this question.

Question: For condensation of pure vapors, if the heat transfer co-efficients in filmwise and drop-wise condensation are respectively hf and hd, then
[A].

hf = hd

[B].

hf > hd

[C].

hf < hd

[D].

hf could be greater or smaller than hd

Answer: Option C

Explanation:

No answer description available for this question.

Question: At steady state the temperature variation in a plane wall, made of two different solids I & II is shown below :The thermal conductivity of material I
[A].

is smaller than that of II.

[B].

is greater than that of II.

[C].

is equal to that of II.

[D].

can be greater than or smaller than that of II.

Answer: Option A

Explanation:

No answer description available for this question.

Question: For shell and tube heat exchanger, with increasing heat transfer area, the purchased cost per unit heat transfer area
[A].

increases

[B].

decreases

[C].

remains constant

[D].

passes through a maxima

Answer: Option D

Explanation:

No answer description available for this question.

Question: In thermal radiation for a black body (where, ε is emissivity and α is absorptivity)
[A].

α = 1; ε ≠ 1

[B].

α ≠ 1, ε = 1

[C].

α ≠ 1, ε ≠ 1

[D].

α = 1; ε = 1

Answer: Option D

Explanation:

No answer description available for this question.

Question: A metal wire of 0.01 m dia and thermal conductivity 200 W/m.K is exposed to a fluid stream with a convective heat transfer coefficient of 100 W/m2.K. The Biot number is
[A].

5.6

[B].

0.025

[C].

3.5

[D].

0.0035

Answer: Option B

Explanation:

No answer description available for this question.

Question: In a heat exchanger with steam outside the tubes, a liquid gets heated to 45°C, when its flow velocity in the tubes is 2 m/s. If the flow velocity is reduced to 1 m/s, other things remaining the same, the temperature of the exit liquid will be
[A].

less than 45°C

[B].

more than 45°C

[C].

equal to 45°C

[D].

initially decreases and remains constant thereafter.

Answer: Option B

Explanation:

No answer description available for this question.