4

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

Absolute temperature (T)

F

T

A. Absolute temperature (T)

4

Stanton number

Biot number

Peclet number

Grashoff number

4

# The concept of overall coefficient of heat transfer is used in heat transfer problems of

Conduction

Convection

Conduction and convection

4

Conduction

Convection

None of these

4

Grashoff number

Nusselt number

Weber number

Prandtl number

4

# Thermal conductivity of air with rise in temperature

Increases

Decreases

Remain constant

May increase or decrease depending on temperature

4

Iron

Concrete

Wood

4

Black body

Grey body

Opaque body

White body

4

# The amount of radiation mainly depends on

Nature of body

Temperature of body

Type of surface of body

All of the above

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

# Joule sec is the unit of

Universal gas constant

Kinematic viscosity

Thermal conductivity

Planck's constant

4

# A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is

h₁ + h₂ + h₃

(h₁.h₂.h₃)1/3

1/h₁ + 1/h₂ + 1/h₃

None of these

4

# Thermal diffusivity is

A dimensionless parameter

Function of temperature

Used as mathematical model

A physical property of the material

4

kcal/m²

kcal/hr °C

kcal/m² hr °C

kcal/m hr °C

4

1 : 1

2 : 1

1 : 2

4 : 1

4

# Conduction is a process of heat transfer

From one particle of the body to another without the actual motion of the particles

From one particle of the body to another by the actual motion of the heated particles

From a hot body to a cold body, in a straight line, without affecting the intervening medium

None of the above

4

# The total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.

Equal to

Directly proportional to

Inversely proportional to

None of these

4

# When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred to as heat transfer by

Conduction

Convection

Conduction and convection

4

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

Absolute temperature (T)

F

T

4

# In a shell and tube heat exchanger, baffles are provided on the shell side to

Improve heat transfer

Provide support for tubes

Prevent stagnation of shell side fluid

All of these

4

Absorptive power

Emissive power

Emissivity

None of these

4

0.1

0.3

0.7

1.7

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

# 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

# Planck's law holds good for

Black bodies

Polished bodies

All coloured bodies

All of the above

4

Watt/cm² °K

Watt/cm4 °K

Watt²/cm °K⁴

Watt/cm² °K⁴

4

Absorptive power

Emissive power

Absorptivity

Emissivity

4

# A composite slab has two layers of different materials with thermal conductivities k₁ and k₂. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be

k₁ k₂

(k₁ + k₂)

(k₁ + k₂)/ k₁ k₂

2 k₁ k₂/ (k₁ + k₂)

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

# 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