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

Three

Four

One

Two

Three

Four

One

Two

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Heat and Mass Transfer
A perfect black body is one which

Reflects all heat

Absorbs heat radiations of all wave lengths falling on it

Is black in colour

Transmits all heat radiations

Reflects all heat

Absorbs heat radiations of all wave lengths falling on it

Is black in colour

Transmits all heat radiations

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Heat and Mass Transfer
When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by

Conduction

Radiation

Conduction and convection

Convection

Conduction

Radiation

Conduction and convection

Convection

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Heat and Mass Transfer
According to Prevost theory of heat exchange

Heat transfer in most of the cases takes place by combination of conduction, convection and radiation

All bodies above absolute zero emit radiation

Heat transfer by radiation requires no medium

It is impossible to transfer heat from low temperature source to t high temperature source

Heat transfer in most of the cases takes place by combination of conduction, convection and radiation

All bodies above absolute zero emit radiation

Heat transfer by radiation requires no medium

It is impossible to transfer heat from low temperature source to t high temperature source

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Heat and Mass Transfer
The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to

Biot number

Peclet number

Grashoff number

Stanton number

Biot number

Peclet number

Grashoff number

Stanton number

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

Absolute temperature

T5

T2

T

Absolute temperature

T5

T2

T

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Heat and Mass Transfer

Heat and Mass Transfer A perfect black body is one which

Heat and Mass Transfer When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by

Heat and Mass Transfer According to Prevost theory of heat exchange

Heat and Mass Transfer The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to

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

Heat and Mass Transfer
A perfect black body is one which

Heat and Mass Transfer
When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by

Heat and Mass Transfer
According to Prevost theory of heat exchange

Heat and Mass Transfer
The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to

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