HEAT AND MASS TRANSFER QUIZ

Which of the following has maximum value of thermal conductivity?

Aluminium

Copper

Brass

Steel

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According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

Fourth power of the absolute temperature

Absolute temperature

Square of the absolute temperature

Cube of the absolute temperature

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According to Wien's law, the wavelength corresponding to maximum energy is proportion to

I²

T

F

Absolute temperature (T)

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Depending on the radiating properties, body will be transparent when (Where a = absorptivity, p = reflectivity, x = transmissivity)

X = 0, a + p = 1

P=1, x = 0, and a = 0

P = 0, x = 0 and a = 1

P = 0, x= 1, and a = 0

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A non-dimensional number generally associated with natural convection heat transfer is

Weber number

Grashoff number

Prandtl number

Nusselt number

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Thermal conductivity of solid metals with rise in temperature normally

Decreases

Remain constant

Increases

May increase or decrease depending on temperature

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The time constant of a thermocouple is

Determined by the time taken to reach 100°C from 0°C

The time taken to attain 50% of the value of initial temperature difference

The time taken to attain 63.2% of the value of initial temperature difference

The time taken to attain the final temperature to be measured

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The unit of Stefan Boltzmann constant is

watt2/cm °K⁴

watt/cm4 °K

watt/cm2 °K⁴

watt/cm3 °K

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The transfer of heat by molecular collision is smallest in

Gases

Liquids

None of these

Solids

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LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is

Higher

Lower

Depends on the area of heat exchanger

Same

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