Heat and Mass Transfer MCQs

Question 1

Which of the following statement is wrong?

Accepted Answer

The thermal conductivity of solid metals increases with rise in temperature

Answer

The heat transfer in liquid and gases takes place according to convection

Answer

The amount of heat flow through a body is dependent upon the material of the body

Answer

Logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference

Question 2

When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,

Accepted Answer

α = 0, ρ = 0 and τ = 1

Answer

α = 1, ρ = 0 and τ = 0

Answer

α = 0, ρ = 1 and τ = 0

Answer

α + ρ = 1 and τ = 0

Question 3

Planck’s law holds good for

Accepted Answer

Black bodies

Answer

Polished bodies

Answer

All coloured bodies

Answer

All of the above

Question 4

Thermal conductivity of a material may be defined as the

Accepted Answer

All of the above

Answer

Quantity of heat flowing in one second through one cm cube of material when opposite faces are maintained at a temperature difference of 1°C

Answer

Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C

Answer

Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces

Question 5

A perfect black body is one which

Accepted Answer

Absorbs heat radiations of all wave lengths falling on it

Answer

Is black in colour

Answer

Reflects all heat

Answer

Transmits all heat radiations

Question 6

Film coefficient is defined as the ratio of

Accepted Answer

Thermal conductivity to the equivalent thickness of the film of fluid

Answer

Temperature drop through the films of fluids to the thickness of film of fluids

Answer

Thickness of film of fluid to the thermal conductivity

Answer

Thickness of film of fluid to the temperature drop through the films of fluids

Question 7

The highest thermal diffusivity is of

Accepted Answer

Lead

Answer

Iron

Answer

Concrete

Answer

Wood

Question 8

The rate of energy transferred by convection to that by conduction is called

Accepted Answer

Nusselt number

Answer

Stanton number

Answer

Biot number

Answer

Peclet number

Question 9

Thermal conductivity of water _________ with rise in temperature.

Accepted Answer

May increase or decrease depending upon temperature

Answer

Remain same

Answer

Decreases

Answer

Increases