4

# Which of the following is a case of steady state heat transfer?

I.C. engine

Air preheaters

Heating of building in winter

None of the above

D. None of the above

4

Wien's law

Planck's law

Stefan's law

Fourier's law

4

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

Absolute temperature

Square of the absolute temperature

Cube of the absolute temperature

Fourth power of the absolute temperature

4

Conduction

Convection

None of these

4

# The use of heat exchangers is made in

Condensers and boilers in steam plants

Condensers and evaporators in refrigeration and air conditioning units

All of the above

4

# Thermal diffusivity of a substance is

Directly proportional to the thermal conductivity

Inversely proportional to density of substance

Inversely proportional to specific heat

All of the above

4

Thermometer

Thermistor

Thermocouple

None of these

4

# Which of the following statement is correct?

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.

4

# Fourier's law of heat conduction gives the heat flow for

Irregular surfaces

Nonuniform temperature surfaces

One dimensional cases only

Two dimensional cases only

4

Parallel flow

Counter flow

Cross flow

All of these

4

# The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is

Equal to one

Greater than one

Less than one

Equal to Nusselt number

4

# A grey body is one whose absorptivity

Varies with temperature

Varies with wavelength of the incident ray

Is equal to its emissivity

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

4

# Depending on the radiating properties, a body will be opaque when

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.

4

Composition

Density

Porosity

All of the above

4

# A perfect black body is one which

Is black in colour

Reflects all heat

Absorbs heat radiations of all wave lengths falling on it

4

# Heat transfer in liquid and gases takes place by

Conduction

Convection

Conduction and convection

4

# Heat transfer by radiation mainly depends upon

Its temperature

Nature of the body

Kind and extent of its surface

All of the above

4

# Thermal conductivity of water in general with rise in temperature

Increases

Decreases

Remain constant

May increase or decrease depending on temperature

4

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

Shorter wavelength

Longer wavelength

Remain same at all wavelengths

Wavelength has nothing to do with it

4

# The amount of radiation mainly depends upon the

Nature of the body

Temperature of the body

Type of surface of the body

All of these

4

Conduction

Convection

Scattering

4

k/h₀

2k/h₀

h₀/k

h₀/2k

4

Pb = pa - pv

Pb = pa + pv

Pb = pa × pv

Pb = pa/pv

4

# The amount of radiation mainly depends on

Nature of body

Temperature of body

Type of surface of body

All of the above

4

# Film coefficient is defined as Inside diameter of tube

Equivalent thickness of film

Thermal conductivity Equivalent thickness of film Specific heat × Viscosity

Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity

Film coefficient × Inside diameter Thermal conductivity

4

# A grey body is one whose absorptivity

Varies with temperature

Varies with the wave length of incident ray

Varies with both

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

4

# Cork is a good insulator because it has

Free electrons

Atoms colliding frequency

Low density

Porous body

4

2 TR

4 TR

8 TR

10 TR

4

# Film coefficient is defined as the ratio of

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

4

# Upto the critical radius of insulation,

Added insulation will increase heat loss

Added insulation will decrease heat loss

Convective heat loss will be less than conductive heat loss

Heat flux will decrease