Thermal conductivity of a material may be defined as the

Heat and Mass Transfer
Thermal conductivity of a material may be defined as the

Quantity of heat flowing in one second through one cm cube of material when opposite faces are maintained at a temperature difference of 1°C

Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces

Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C

All of these

Quantity of heat flowing in one second through one cm cube of material when opposite faces are maintained at a temperature difference of 1°C

Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces

Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C

All of these

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Heat and Mass Transfer
Emissivity of a white polished body in comparison to a black body is

Depends upon the shape of body

Same

Lower

Higher

Depends upon the shape of body

Same

Lower

Higher

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Heat and Mass Transfer
A designer chooses the values of fluid flow rates and specific heats in such a manner that the heat capacities of the two fluids are equal. A hot fluid enters the counter flow heat exchanger at 100°C and leaves at 60°C. A cold fluid enters the heat exchanger at 40°C. The mean temperature difference between the two fluids is

66.7°C

40°C

60°C

20°C

66.7°C

40°C

60°C

20°C

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Heat and Mass Transfer
Which of the following would lead to a reduction in thermal resistance?

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

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

All of these

In radiation, increasing the temperature and reducing the emissivity.

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

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

All of these

In radiation, increasing the temperature and reducing the emissivity.

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Heat and Mass Transfer
An ordinary passenger aircraft requires a cooling system of capacity.

10 TR

4 TR

2 TR

8 TR

10 TR

4 TR

2 TR

8 TR

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Heat and Mass Transfer
The critical thickness of insulation for a sphere is

k/h₀

h₀/2k

2k/h₀

h₀/k

k/h₀

h₀/2k

2k/h₀

h₀/k

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Heat and Mass Transfer

Heat and Mass Transfer Thermal conductivity of a material may be defined as the

Heat and Mass Transfer Emissivity of a white polished body in comparison to a black body is

Heat and Mass Transfer Which of the following would lead to a reduction in thermal resistance?

Heat and Mass Transfer An ordinary passenger aircraft requires a cooling system of capacity.

Heat and Mass Transfer The critical thickness of insulation for a sphere is

Heat and Mass Transfer
Thermal conductivity of a material may be defined as the

Heat and Mass Transfer
Emissivity of a white polished body in comparison to a black body is

Heat and Mass Transfer
Which of the following would lead to a reduction in thermal resistance?

Heat and Mass Transfer
An ordinary passenger aircraft requires a cooling system of capacity.

Heat and Mass Transfer
The critical thickness of insulation for a sphere is