HEAT AND MASS TRANSFER QUIZ

Conduction is a process of heat transfer

From a hot body to a cold body, in a straight line, without affecting the intervening medium

From one particle of the body to another without the actual motion of the particles

From one particle of the body to another by the actual motion of the heated particles

None of these

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Thermal conductivity of air with rise in temperature

Increases

Remain constant

May increase or decrease depending on temperature

Decreases

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The emissive power of a body depends upon its

Physical nature

Temperature

All of these

Wave length

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A grey body is one whose absorptivity

Does not vary with temperature and. wavelength of the incident ray

Varies with temperature

Varies with wavelength of the incident ray

Is equal to its emissivity

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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

One

Three

Four

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Unit of thermal diffusivity is

kcal/m. hr °C

m²/hr

m²/hr °C

kcal/m² hr

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Emissivity of a white polished body in comparison to a black body is

Same

Depends upon the shape of body

Lower

Higher

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Thermal conductivity of water _________ with rise in temperature.

Increases

May increase or decrease depending upon temperature

Decreases

Remain same

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The value of the wave length for maximum emissive power is given by

Stefan’s law

Kirchhoff’s law

Wine’s law

Planck’s law

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The value of Prandtl number for air is about

0.7

0.1

1.7

0.3

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