Mechanical Engineering

Question: A furnace is made of a red brick wall of thickness 0.5 m and conductivity 0.7 W/mK. For the same heat loss and temperature drop, this can be replaced by a layer of diatomite earth of conductivity 0.14 W/mK and thickness
[A].

0.5 m

[B].

0.1 m

[C].

0.2 m

[D].

0.5 m

Answer: Option B

Explanation:

No answer description available for this question.

Question: A composite slab has two layers of different materials with thermal conductivities k1 and k2. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be
[A].

k1k2

[B].

k1 + k2

[C].

[D].

Answer: Option D

Explanation:

No answer description available for this question.

Question: Which of the following would lead to a reduction in thermal resistance?
[A].

In conduction, reduction in the thickness of the material and an increase in thermal conductivity.

[B].

In convection, stirring of the fluid and cleaning the heating surface.

[C].

In radiation, increasing the temperature and reducing the emissivity.

[D].

all of the above

Answer: Option D

Explanation:

No answer description available for this question.

Question: A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,
[A].

the better insulation must be put inside

[B].

the better insulation must be put outside

[C].

one could place either insulation on either side

[D].

one should take into account the steam temperature before deciding as to which insulation is put where

Answer: Option A

Explanation:

No answer description available for this question.

Question: The average value of thermal conductivity for water at 20° C saturate is about 0.51.
[A].

True

[B].

False

Answer: Option A

Explanation:

No answer description available for this question.

Question: According to Newton’s law of cooling, the heat transfer from a hot body to a cold body is
[A].

directly proportional to the surface area

[B].

directly proportional to the difference of temperatures between the two bodies

[C].

either (a) or (b)

[D].

both (a) and (b)

Answer: Option D

Explanation:

No answer description available for this question.

Question: The amount of heat flow through a body by conduction is
[A].

directly proportional to the surface area of the body

[B].

directly proportional to the temperature difference on the two faces of the body

[C].

inversely proportional to the thickness of the body

[D].

all of the above

Answer: Option D

Explanation:

No answer description available for this question.

Question: Fourier’s law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow, and k = Thermal conductivity of the body)
[A].

[B].

[C].

[D].

Answer: Option A

Explanation:

No answer description available for this question.

Question: In case of liquids and gases, the heat transfer takes place according to
[A].

conduction

[B].

convection

[C].

radiation

[D].

none of these

Answer: Option B

Explanation:

No answer description available for this question.

Question: In case of solids, the heat transfer takes place according to radiation.
[A].

Correct

[B].

Incorrect

Answer: Option B

Explanation:

No answer description available for this question.