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

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

All of these

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

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

All of these

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Heat and Mass Transfer
Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be

Two

One

Three

Four

Two

One

Three

Four

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Heat and Mass Transfer
In case of liquids and gases, the heat transfer takes place according to

Convection

Conduction

Radiation

None of these

Convection

Conduction

Radiation

None of these

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

In radiation, increasing the temperature and reducing the emissivity.

All of these

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.

In radiation, increasing the temperature and reducing the emissivity.

All of these

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.

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Heat and Mass Transfer
A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is

h₁ + h₂ + h₃

(h₁.h₂.h₃)1/3

1/h₁ + 1/h₂ + 1/h₃

None of these

h₁ + h₂ + h₃

(h₁.h₂.h₃)1/3

1/h₁ + 1/h₂ + 1/h₃

None of these

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Heat and Mass Transfer
The value of Prandtl number for air is about

1.7

0.3

0.1

0.7

1.7

0.3

0.1

0.7

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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 In case of liquids and gases, the heat transfer takes place according to

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

Heat and Mass Transfer A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is

Heat and Mass Transfer The value of Prandtl number for air is about

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

Heat and Mass Transfer
In case of liquids and gases, the heat transfer takes place according to

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

Heat and Mass Transfer
A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is

Heat and Mass Transfer
The value of Prandtl number for air is about