α = 1, ρ = 0 and τ = 0

α = 0, ρ = 1 and τ = 0

α = 0, ρ = 0 and τ = 1

α + ρ = 1 and τ = 0

D. α + ρ = 1 and τ = 0

The total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature

The wave length corresponding to the maximum energy is proportional to the absolute temperature

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

None of the above

P = 0, x = 0 and a = 1

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

P = 0, T= 1, and a = 0

X = 0, a + p = 1

Directly proportional to the surface area of the body

Directly proportional to the temperature difference on the two faces of the body

Dependent upon the material of the body

All of the above

Change vapour into liquid

Change liquid into vapour

Increase the temperature of a liquid or vapour

Convert water into steam and superheat it

Stanton number

Nusselt number

Biot number

Peclet number

A dimensionless parameter

Function of temperature

Used as mathematical model

A physical property of the material

The time taken to attain the final temperature to be measured

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

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

m²/hr

m²/hr °C

kcal/m² hr

kcal/m. hr °C

RN = hl/k

RN = μ cp/k

RN = ρ V l /μ

RN = V²/t.cp

Convection

Radiation

Forced convection

Free convection

1 : 1

2 : 1

1 : 2

4 : 1

More than those for liquids

Less than those for liquids

More than those for solids

Dependent on the viscosity

Same

Less

Greater

None of these

Maximum

Minimum

Zero

None of these

Thermal conductivity to the equivalent thickness of the film of fluid

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

Thickness of film of fluid to the thermal conductivity

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

Grashoff number

Biot number

Stanton number

Prandtl number

_{m} = (Δt_{1} - Δt_{2})/ log_{e} (Δt_{1}/Δt_{2})

_{m} = log_{e} (Δt_{1}/Δt_{2})/ (Δt_{1} - Δt_{2})

_{m} = t_{m} = (Δt_{1} - Δt_{2}) log_{e} (Δt_{1}/Δt_{2})

_{m} = log_{e} (Δt_{1} - Δt_{2})/ Δt_{1}/Δt_{2}

Function of temperature

Physical property of a substance

Dimensionless parameter

All of these

A grey body is one which absorbs all radiations incident on it.

At thermal equilibrium, the emissivity and absorptivity are same.

The energy absorbed by a body to the total energy falling on it, is called emissivity.

A perfect body is one which is black in colour.

Higher

Lower

Same

Depends on the area of heat exchanger

Thermal conductivity

Thermal diffusivity

Density

Dynamic viscosity

Directly proportional to the surface area

Directly proportional to the difference of temperatures between the two bodies

Either (A) or (B)

Both (A) and (B)

Glass

Water

Plastic

Air

α = 1, ρ = 0 and τ = 0

α = 0, ρ = 1 and τ = 0

α = 0, ρ = 0 and τ = 1

α + ρ = 1 and τ = 0

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

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

The thermal conductivity of solid metals increases with rise in temperature

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

Black bodies

Polished bodies

All coloured bodies

All of the above

0.1

0.23

0.42

0.51

Thermal resistance

Thermal coefficient

Temperature gradient

Thermal conductivity

First law of thermodynamics

Newton's law of cooling

Newton's law of heating

Stefan's law

P = 0, x = 0 and a = 1

P=1, x = 0 and a = 0

P = 0, x = 1 and a = 0

X = 0, a + p = 1 Where a = absorptivity, p = reflectivity, X = transmissivity.