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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/hC) 2k/h D) k/h

Category: Mechanical Engineering MCQs

Sub Category: Heat Transfer Mcqs

397 Related Questions Q:

Maximum value of critical radius is

Q:

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?

Q:

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

Q:

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?

Q:

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?

Q:

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

Q:

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

Q:

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

(i) Energy of a nuclear reactor

(ii) Liberation of energy due to some exothermic chemical reactions

(iii) Resistance heating in electrical appliances

Which of the statements made above are correct?

Q:

The temperature drop in a plane wall with uniformly distributed heat generation can be decreased by reducing

Q:

There occurs heat conduction and internal heat generation at uniform rate within the conduction medium itself in the following cases

(i) Drying of concrete

(ii) Chemical processes

(iii) Fuel elements in a nuclear reaction

Choose the correct option

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## 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

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

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

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?

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

Sanfoundry Global Education & Learning Series – Heat Transfer.

To practice all areas of Heat Transfer for freshers, here is complete set of 1000+ Multiple Choice Questions and Answers.

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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

### 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?

Let us say thermal conductivity of a wall is governed by the relation k = k0 (1 + α t). In that case the temperature at the mid-plane of the heat conducting wall would be

A steel pipe of 20 mm inner diameter and 2 mm thickness is covered with 20 mm thick of fiber glass insulation (k = 0.05 W/m degree). If the inside and outside convective coefficients are 10 W/m² degree and 5 W/m² degree, calculate the overall heat transfer coefficient based on inside diameter of pipe. In the diagram, the diameter of small circle is 20 mm

Which is true regarding a complete rectangular furnace?

A pipe of outside diameter₂0 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 pipe?

A rod of 3 cm diameter and 20 cm length is maintained at 100 degree Celsius at one end and 10 degree Celsius at the other end. These temperature conditions are attained when there is heat flow rate of 6 W. If cylindrical surface of the rod is completely insulated, determine the thermal conductivity of the rod material

Three metal walls of same thickness and cross sectional area have thermal conductivities k, 2k and 3k respectively. The temperature drop across the walls (for same heat transfer) will be in the ratio

The oven of an electric store, of total outside surface area 2.9 m² dissipates electric energy at the rate of 600 W. The surrounding room air is at 20 degree Celsius and the surface coefficient of heat transfer between the room air and the surface of the oven is estimated to be 11.35 W/m² degree. Determine the average steady state temperature of the outside surface of the store

In Cartesian coordinates the heat conduction equation is given by

The rate of convective heat transfer between a solid boundary and adjacent fluid is given by

A plane wall of thickness δ has its surfaces maintained at temperatures T₁ and T₂. The wall is made of a material whose thermal conductivity varies with temperature according to the relation k = k₀ T². Find the expression to work out the steady state heat conduction through the wall?

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?

The following data pertains to a hollow cylinder and a hollow sphere made of same material and having the same temperature drop over the wall thickness

Inside radius = 0.1 m and outside surface area = 1 square meter

If the outside radius for both the geometrics is same, calculate the ratio of heat flow in the cylinder to that of sphere?

The mean thermal conductivity evaluated at the arithmetic mean temperature is represented by

“Radiation cannot be affected through vacuum or space devoid of any matter”. True or false

A composite wall is made of two layers of thickness δ₁ and δ₂ having thermal conductivities k and 2k and equal surface area normal to the direction of heat flow. The outer surface of composite wall are at 100 degree Celsius and 200 degree Celsius. The minimum surface temperature at the junction is 150 degree Celsius. What will be the ratio of wall thickness?

Let us assume two walls of same thickness and cross-sectional area having thermal conductivities in the ratio 1/2. Let us say there is same temperature difference across the wall faces, the ratio of heat flow will be

Maximum value of critical radius is

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

The rate of heat transfer for a plane wall of homogenous material with constant thermal conductivity is given by

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Mohammed 7 day ago

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