Heat Transfer Test

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Heat Transfer Test - 5

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Weekly Quiz Competition

Question 1
4 / -1

What are the relevant boundary conditions in case of heat transfer from a bar connected to two heat sources at different temperatures?

A
α = α₁ at x = 1 and α = α₂at x = 2L

B
α = α₁ at x = 0 and α = α₂at x = infinity

C
α = α₁ at x = 0 and α = α₂at x = L

D
α = α₁ at x = infinity and α = α₂at x = 1

Solution

It should be at x = o and x = L.
Question 2
4 / -1

Radiation heat transfer is characterized by

A
Movement of discrete packets of energy as electromagnetic waves

B
Due to bulk fluid motion, there is a transport of energy

C
There is the circulation of fluid by buoyancy effects

D
Thermal energy transfer as vibrational energy in the lattice structure of the material

Solution

EM waves is characterized by radiant heat transfer.
Question 3
4 / -1

A thin metal plate of 4 cm diameter is suspended in atmospheric air whose temperature is 290 K. This plate attains a temperature of 295 K when one of its faces receives radiant energy from a heat source at the rate of 2 W. If heat transfer coefficient on both surfaces of the plate is stated to be 87.5 W/m ² K, workout the reflectivity of the plate.

A
0.15

B
0.55

C
0.25

D
0.45

Solution

Heat loss by convection from both sides of the plates = 2 h A d t = 1.1 W. Energy lost by reflection = 2.0 – 1.1 = 0.9 W.
Question 4
4 / -1

The radiant heat transfer from a plate of 2.5 cm² area at 1250 K to a very cold enclosure is 5.0 W. Determine the emissivity of the plate at this temperature

A
0.544

B
0.144

C
0.044

D
0.244

Solution

Emissivity = E/σ A T⁴ = 0.144.
Question 5
4 / -1

The calculation of heat transmission by convection is based on the determination of a Nusselt number or convective film coefficient. To that goal, which of the following strategies have been proposed

(i) Non-dimensional analysis and experimental correlations

(ii) Hydrodynamic concept of velocity boundary layer

(iii) Reynolds similarity between the mechanism of fluid friction in the boundary layer and the transfer of heat by convection

Identify the correct one

A
ii and iii

B
i and iii

C
i, ii, and iii

D
i and ii

Solution

It should be a dimensional analysis and experimental correlations.
Question 6
4 / -1

The non-dimensional parameter known as Stanton number is used in which of the following heat transfer?

A
Natural convection heat transfer

B
Unsteady state heat transfer

C
Condensation heat transfer

D
Forced convection heat transfer

Solution

It’s the ratio of the heat transfer coefficient to the heat flow per unit temperature rise caused by fluid velocity. It can only be used for forced convection heat transfer.
Question 7
4 / -1

The convective heat transfer coefficient in the laminar flow over a flat plate __________

A
Decreases with increase in free stream velocity

B
Increases if a denser fluid is used

C
Increases with distance

D
Increases if a higher viscosity fluid is used

Solution

It mostly increases if a denser fluid is used.
Question 8
4 / -1

Maximum heat transfer rate in a modern boiler is about

A
4 * 10 ⁵ W/m²

B
5 * 10 ⁵ W/m²

C
3 * 10 ⁵ W/m²

D
2 * 10 ⁵ W/m²

Solution

Greater importance has recently been given to the boiling heat transfer.
Question 9
4 / -1

In spite of the large heat transfer coefficient in boiling liquids, fins are used advantageously when the entire surface is exposed to

A
Nucleate boiling

B
Film boiling

C
Transition boiling

D
All modes of boiling

Solution

Here all modes of boiling i.e. film, transition and nucleate are of great importance.
Question 10
4 / -1

Which of the following is the unit of coefficient of radiant heat transfer?

A
W/m²

B
W/m K

C
W/m² K

D
W/K

Solution

Its value can be calculated from the heat flux equation for any configuration.

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Heat Transfer Test - 5

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Heat Transfer Test - 5

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Question 1

α = α 1 at x = 1 and α = α 2 at x = 2L

α = α 1 at x = 0 and α = α 2 at x = infinity

α = α 1 at x = 0 and α = α 2 at x = L

α = α 1 at x = infinity and α = α 2 at x = 1

Solution

Question 2

Movement of discrete packets of energy as electromagnetic waves

Due to bulk fluid motion, there is a transport of energy

There is the circulation of fluid by buoyancy effects

Thermal energy transfer as vibrational energy in the lattice structure of the material

Solution

Question 3

0.15

0.55

0.25

0.45

Solution

Question 4

0.544

0.144

0.044

0.244

Solution

Question 5

ii and iii

i and iii

i, ii, and iii

i and ii

Solution

Question 6

Natural convection heat transfer

Unsteady state heat transfer

Condensation heat transfer

Forced convection heat transfer

Solution

Question 7

Decreases with increase in free stream velocity

Increases if a denser fluid is used

Increases with distance

Increases if a higher viscosity fluid is used

Solution

Question 8

4 * 10 5 W/m2

5 * 10 5 W/m2

3 * 10 5 W/m2

2 * 10 5 W/m2

Solution

Question 9

Nucleate boiling

Film boiling

Transition boiling

All modes of boiling

Solution

Question 10

W/m2

W/m K

W/m2 K

W/K

Solution

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α = α₁ at x = 1 and α = α₂at x = 2L

α = α₁ at x = 0 and α = α₂at x = infinity

α = α₁ at x = 0 and α = α₂at x = L

α = α₁ at x = infinity and α = α₂at x = 1

4 * 10 ⁵ W/m²

5 * 10 ⁵ W/m²

3 * 10 ⁵ W/m²

2 * 10 ⁵ W/m²

W/m²

W/m² K