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## For an object i.e. spherical the value of critical radius would be

MCQs: For an object i.e. spherical the value of critical radius would be - (A) 2k/3h - (B) 3k/h

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Question & Answer Q:

For an object i.e. spherical the value of critical radius would be

**A)**2k/3h

**B)**3k/h

**C)**2k/h

**D)**k/h

View Answer Explanation

Category: Mechanical Engineering MCQs

Sub Category: Heat Transfer Mcqs

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Maximum value of critical radius is

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An electric cable of aluminum (k = 240 W/ m degree) is to be insulated with rubber (k = 6 W/ square meter degree). If the cable is in air (h = 6 W/square meter degree). Find the critical radius?

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The value of critical radius in case of a cylindrical hollow object is

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A wire of radius 3 mm and 1.25 m length is to be maintained at 60 degree Celsius by insulating it by a material of thermal conductivity 0.175 W/m K. The temperature of surrounding is 20 degree Celsius with heat transfer coefficient 8.5 W/ m² K. Find percentage increase in heat loss due to insulation?

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A pipe of outside diameter 20 mm is to be insulated with asbestos which has a mean thermal conductivity of 0.1 W/m degree. The local coefficient of convective heat to the surroundings is 5 W/square meter degree. Find the critical radius of insulation for optimum heat transfer from a pipe?

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For insulation to be properly effective in restricting heat transmission, the pipe radius r₀ will be

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In case of heat conduction through the plane wall, which one of the following is not a correct assumption?

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otable example of uniform generation of heat within the conducting medium are

(i) Energy of a nuclear reactor

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(iii) Resistance heating in electrical appliances

Which of the statements made above are correct?

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Choose the correct option

## Heat Transfer Questions and Answers for Freshers

This set of Heat Transfer Questions & Answers for freshers focuses on “Critical Thickness Of Insulation”. 1. A cable of 10 mm outside is to be laid in an atmosphere of 25 degree Celsius (h = 12.5 W/m2 degree) and its surface temperature is likely to be 75 degree Celsius due to heat generated within ... Read more

## Heat Transfer Questions and Answers – Critical Thickness of Insulation

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This set of Heat Transfer Questions & Answers for freshers focuses on “Critical Thickness Of Insulation”.

1. A cable of 10 mm outside is to be laid in an atmosphere of 25 degree Celsius (h = 12.5 W/m2 degree) and its surface temperature is likely to be 75 degree Celsius due to heat generated within it. How would the heat flow from the cable be affected if it is insulated with rubber having thermal conductivity k = 0.15 W/m degree?

a) 43.80 W per meter length

b) 53.80 W per meter length

c) 63.80 W per meter length

d) 73.80 W per meter length

View Answer

2. Chose the correct one with respect to the critical radius of insulation

a) There is more heat loss i.e. conductive

b) There occurs a decrease in heat flux

c) Heat loss increases with addition of insulation

d) Heat loss decreases with addition of insulation

View Answer

3. A heat exchanger shell of outside radius 15 cm is to be insulated with glass wool of thermal conductivity 0.0825 W/m degree. The temperature at the surface is 280 degree Celsius and it can be assumed to remain constant after the layer of insulation has been applied to the shell. The convective film coefficient between the outside surface of glass wool and the surrounding air is estimated to be 8 W/m2 degree. What is the value of a critical radius?

a) 9.31 mm b) 10.31 mm c) 11.31 mm d) 12.31 mm View Answer

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4. For an object i.e. spherical the value of critical radius would be

a) 2k/3h b) 3k/h c) 2k/h d) k/h View Answer

5. Maximum value of critical radius is

a) 0.01 m b) 0.04 m c) 0.06 m d) 0.0001 m View Answer

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6. An electric cable of aluminum (k = 240 W/ m degree) is to be insulated with rubber (k = 6 W/ square meter degree). If the cable is in air (h = 6 W/square meter degree). Find the critical radius?

a) 80 mm b) 160 mm c) 40 mm d) 25 mm View Answer

7. The value of critical radius in case of a cylindrical hollow object is

a) 2k/h b) 2h/k c) k/h d) h/k View Answer advertisement

8. A wire of radius 3 mm and 1.25 m length is to be maintained at 60 degree Celsius by insulating it by a material of thermal conductivity 0.175 W/m K. The temperature of surrounding is 20 degree Celsius with heat transfer coefficient 8.5 W/ m2 K. Find percentage increase in heat loss due to insulation?

a) 134.46 % b) 124.23 % c) 100.00 % d) 12.55 % View Answer

9. A pipe of outside diameter 20 mm is to be insulated with asbestos which has a mean thermal conductivity of 0.1 W/m degree. The local coefficient of convective heat to the surroundings is 5 W/square meter degree. Find the critical radius of insulation for optimum heat transfer from a pipe?

a) 10 mm b) 20 mm c) 30 mm d) 40 mm View Answer advertisement

10. For insulation to be properly effective in restricting heat transmission, the pipe radius r0 will be

a) Greater than critical radius

b) Less than critical radius

c) Equal to critical radius

d) Greater than or equal to critical radius

View Answer

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## For an object i.e. spherical the value of critical radius would be

For an object i.e. spherical the value of critical radius would be 2k/3h 3k/h 2k/h k/h. Heat Transfer Objective type Questions and Answers.

## E-PolyLearning

E-PolyLearning Discussion Forum

Que. For an object i.e. spherical the value of critical radius would be

a. 2k/3h b. 3k/h c. 2k/h d. k/h Correct Answer:2k/h

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### More Questions Like this:

A cable of 10 mm outside is to be laid in an atmosphere of 25 degree Celsius (h = 12.5 W/m² degree) and its surface temperature is likely to be 75 degree Celsius due to heat generated within it. How would the heat flow from the cable be affected if it is insulated with rubber having thermal conductivity k = 0.15 W/m degree?

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Maximum value of critical radius is

For an object i.e. spherical the value of critical radius would be

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