Heat Transfer MCQs

Question 1

Heat conducted through unit area and unit thick face per unit time when temperature difference between opposite faces is unity, is called

Accepted Answer

Thermal conductivity

Answer

Thermal resistance

Answer

Thermal coefficient

Answer

Temperature gradient

Question 2

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

Accepted Answer

Grashof number

Answer

Nusselt number

Answer

Weber number

Answer

Prandtl number

Question 3

According of Kirchhoff's law

Accepted Answer

Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body

Answer

Radiant heat is proportional to fourth power of absolute temperature

Answer

Emissive power and absorptivity are constant for all bodies

Answer

Ratio of emissive power to absorptive power is maximum for perfectly black body

Question 4

The energy distribution of an ideal reflector at higher temperatures is largely in the range of

Accepted Answer

Shorter wavelength

Answer

Longer wavelength

Answer

Remains same at all wavelengths

Answer

Wavelength has nothing to do with it

Question 5

The thermal diffusivities for solids are generally

Accepted Answer

Inorg than those for liquids and gases

Answer

Less than those for gases

Answer

Jess than those for liquids

Answer

More or less same as for liquids and gases

Question 6

Thermal diffusivity of a substance is

Accepted Answer

All of the above

Answer

Directly proportional to thermal conductivity

Answer

Inversely proportional to density of substance

Answer

Inversely proportional to specific heat

Question 7

At thermal equilibrium

Accepted Answer

Absorptivity is equal to emissivity

Answer

Absorptivity is greater than emissivity

Answer

Absorptivity is lesser than emissivity

Answer

Sum of absorptivity and emissivity is unity

Question 8

40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is

Accepted Answer

0.45

Answer

0.55

Answer

0.40

Answer

0.75

Question 9

A grey body is one whose absorptivity

Accepted Answer

Does not vary with temperature and wave length of the incident ray

Answer

Varies with temperature

Answer

Varies with the wave length of incident ray

Answer

Varies with both