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

Three

Four

One

Two

Three

Four

One

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Heat and Mass Transfer
The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles due to difference of density caused by temperature of the particle is known as

Conduction

Forced convection

Radiation

Free convection

Conduction

Forced convection

Radiation

Free convection

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Heat and Mass Transfer
According to Prevost theory of heat exchange

Heat transfer by radiation requires no medium

All bodies above absolute zero emit radiation

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

Heat transfer by radiation requires no medium

All bodies above absolute zero emit radiation

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

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Heat and Mass Transfer
According to Newton's law of cooling, the heat transfer from a hot body to a cold body is

Directly proportional to the surface area

Both (A) and (B)

Directly proportional to the difference of temperatures between the two bodies

Either (A) or (B)

Directly proportional to the surface area

Both (A) and (B)

Directly proportional to the difference of temperatures between the two bodies

Either (A) or (B)

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Heat and Mass Transfer
In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by

Conduction

Convection

Both convection and conduction

Radiation

Conduction

Convection

Both convection and conduction

Radiation

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Heat and Mass Transfer
Sensible heat factor is given by (where S.H. = Sensible heat, and L.H. = Latent heat)

S.H/(S.H + L.H)

(S.H + L.H) /S.H

S.H/(L.H - S.H)

(L.H - S.H)/S.H

S.H/(S.H + L.H)

(S.H + L.H) /S.H

S.H/(L.H - S.H)

(L.H - S.H)/S.H

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Heat and Mass Transfer

Heat and Mass Transfer The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles due to difference of density caused by temperature of the particle is known as

Heat and Mass Transfer According to Prevost theory of heat exchange

Heat and Mass Transfer According to Newton's law of cooling, the heat transfer from a hot body to a cold body is

Heat and Mass Transfer In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by

Heat and Mass Transfer Sensible heat factor is given by (where S.H. = Sensible heat, and L.H. = Latent heat)

Heat and Mass Transfer
The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles due to difference of density caused by temperature of the particle is known as

Heat and Mass Transfer
According to Prevost theory of heat exchange

Heat and Mass Transfer
According to Newton's law of cooling, the heat transfer from a hot body to a cold body is

Heat and Mass Transfer
In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by

Heat and Mass Transfer
Sensible heat factor is given by (where S.H. = Sensible heat, and L.H. = Latent heat)