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

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

Four

Three

One

Two

Four

Three

One

Two

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Heat and Mass Transfer
Joule sec is the unit of

Kinematic viscosity

Universal gas constant

Planck's constant

Thermal conductivity

Kinematic viscosity

Universal gas constant

Planck's constant

Thermal conductivity

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Heat and Mass Transfer
Metals are good conductors of heat because

They contain free electrons

Their atoms collide frequently

Their atoms are relatively far apart

They have high density

They contain free electrons

Their atoms collide frequently

Their atoms are relatively far apart

They have high density

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Heat and Mass Transfer
Thermal conductivity of non-metallic amorphous solids with decrease in temperature

Remain constant

May increase or decrease depending on temperature

Increases

Decreases

Remain constant

May increase or decrease depending on temperature

Increases

Decreases

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Heat and Mass Transfer
Planck’s law holds good for

All of these

all coloured bodies

black bodies

polished bodies

All of these

all coloured bodies

black bodies

polished bodies

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Heat and Mass Transfer
According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

Absolute temperature

Square of the absolute temperature

Fourth power of the absolute temperature

Cube of the absolute temperature

Absolute temperature

Square of the absolute temperature

Fourth power of the absolute temperature

Cube of the absolute temperature

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Heat and Mass Transfer

Heat and Mass Transfer Joule sec is the unit of

Heat and Mass Transfer Metals are good conductors of heat because

Heat and Mass Transfer Thermal conductivity of non-metallic amorphous solids with decrease in temperature

Heat and Mass Transfer Planck’s law holds good for

Heat and Mass Transfer According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

Heat and Mass Transfer
Joule sec is the unit of

Heat and Mass Transfer
Metals are good conductors of heat because

Heat and Mass Transfer
Thermal conductivity of non-metallic amorphous solids with decrease in temperature

Heat and Mass Transfer
Planck’s law holds good for

Heat and Mass Transfer
According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the