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

One

Four

Two

Three

One

Four

Two

Three

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Heat and Mass Transfer
Stefan Boltzmann law is applicable for heat transfer by

Radiation

Conduction

Conduction and radiation combined

Convection

Radiation

Conduction

Conduction and radiation combined

Convection

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Heat and Mass Transfer
The expression Q = ρ AT4 is called

Joseph-Stefan equation

Fourier equation

Newton Reichmann equation

Stefan-Boltzmann equation

Joseph-Stefan equation

Fourier equation

Newton Reichmann equation

Stefan-Boltzmann equation

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Heat and Mass Transfer
The most commonly used method for the design of duct size is the

Velocity reduction method

Static regains method

Equal friction method

Dual or double method

Velocity reduction method

Static regains method

Equal friction method

Dual or double method

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

All of these

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

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

All of these

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

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

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Heat and Mass Transfer
The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.

None of these

Inversely proportional to

Equal to

Directly proportional to

None of these

Inversely proportional to

Equal to

Directly proportional to

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Heat and Mass Transfer

Heat and Mass Transfer Stefan Boltzmann law is applicable for heat transfer by

Heat and Mass Transfer The expression Q = ρ AT4 is called

Heat and Mass Transfer The most commonly used method for the design of duct size is the

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

Heat and Mass Transfer The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.

Heat and Mass Transfer
Stefan Boltzmann law is applicable for heat transfer by

Heat and Mass Transfer
The expression Q = ρ AT4 is called

Heat and Mass Transfer
The most commonly used method for the design of duct size is the

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

Heat and Mass Transfer
The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.