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

Two

Four

One

Three

Two

Four

One

Three

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Heat and Mass Transfer
The product of Reynolds number and Prandtl number is known as

Biot number

Grashoff number

Peclet number

Stanton number

Biot number

Grashoff number

Peclet number

Stanton number

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Heat and Mass Transfer
Heat flows from one body to other when they have

Different specific heat

Different atomic structure

Different temperatures

Different heat contents

Different specific heat

Different atomic structure

Different temperatures

Different heat contents

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Heat and Mass Transfer
Depending on the radiating properties, a body will be white when(Where a = absorptivity, p = reflectivity, x = transmissivity)

P = 0, x = 1 and a = 0

P = 0, x = 0 and a = 1

P=1, T = 0 and a = 0

X = 0, a + p = 1

P = 0, x = 1 and a = 0

P = 0, x = 0 and a = 1

P=1, T = 0 and a = 0

X = 0, a + p = 1

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Heat and Mass Transfer
Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of

0.1

0.002

0.02

0.01

0.1

0.002

0.02

0.01

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Heat and Mass Transfer
Upto the critical radius of insulation,

Added insulation will decrease heat loss

Added insulation will increase heat loss

Convective heat loss will be less than conductive heat loss

Heat flux will decrease

Added insulation will decrease heat loss

Added insulation will increase heat loss

Convective heat loss will be less than conductive heat loss

Heat flux will decrease

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Heat and Mass Transfer

Heat and Mass Transfer The product of Reynolds number and Prandtl number is known as

Heat and Mass Transfer Heat flows from one body to other when they have

Heat and Mass Transfer Depending on the radiating properties, a body will be white when(Where a = absorptivity, p = reflectivity, x = transmissivity)

Heat and Mass Transfer Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of

Heat and Mass Transfer Upto the critical radius of insulation,

Heat and Mass Transfer
The product of Reynolds number and Prandtl number is known as

Heat and Mass Transfer
Heat flows from one body to other when they have

Heat and Mass Transfer
Depending on the radiating properties, a body will be white when(Where a = absorptivity, p = reflectivity, x = transmissivity)

Heat and Mass Transfer
Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of

Heat and Mass Transfer
Upto the critical radius of insulation,