4

# Emissivity of a white polished body in comparison to a black body is

Higher

Lower

Same

Depends upon the shape of body

B. Lower

4

# The most commonly used method for the design of duct size is the

Velocity reduction method

Equal friction method

Static regains method

Dual or double method

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

Iron

Concrete

Wood

4

# The heat is transferred by conduction, convection and radiation in

Melting of ice

Boiler furnaces

Condensation of steam in condenser

None of these

4

# Which of the following property of air does not increase with rise in temperature?

Thermal conductivity

Thermal diffusivity

Density

Dynamic viscosity

4

Stanton number

Nusselt number

Biot number

Peclet number

4

# Heat flows from one body to other when they have

Different heat contents

Different specific heat

Different atomic structure

Different temperatures

4

# Which of the following would lead to a reduction in thermal resistance?

In conduction, reduction in the thickness of the material and an increase in thermal conductivity.

In convection, stirring of the fluid and cleaning the heating surface.

In radiation, increasing the temperature and reducing the emissivity.

All of the above

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

Stanton number

Biot number

Peclet number

Grashoff number

4

# The natural convection air cooled condensers are used in

Domestic refrigerators

Water coolers

Room air conditioners

All of these

4

Wien's law

Planck's law

Stefan's law

Fourier's law

4

Conduction

Convection

None of these

4

# Pick up the wrong case. Heat flowing from one side to other depends directly on

Face area

Time

Thickness

Temperature difference

4

# Unit of thermal conductivity in S.I. units is

J/m² sec

J/m °K sec

W/m °K

Option (B) and (C) above

4

# Absorptivity of a body will be equal to its emissivity

At all temperatures

At one particular temperature

When system is under thermal equilibrium

At critical temperature

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

One

Two

Three

Four

4

Conduction

Convection

4

# Emissivity of a white polished body in comparison to a black body is

Higher

Lower

Same

Depends upon the shape of body

4

# Log mean temperature difference in case of counter flow compared to parallel flow will be

Same

More

Less

Depends on other factors

4

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

Thermal resistance

Thermal coefficient

Thermal conductivity

4

# The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles caused by some mechanical means, is known as

Conduction

Free convection

Forced convection

4

h = k/ ρS

h = ρS/k

h = S/ρk

h = kρ/S

4

# Thermal conductivity of solid metals with rise in temperature normally

Increases

Decreases

Remain constant

May increase or decrease depending on temperature

4

Conduction

Convection

None of these

4

S.H/(S.H + L.H)

(S.H + L.H) /S.H

(L.H - S.H)/S.H

S.H/(L.H - S.H)

4

# The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body

Move actually

Do not move actually

Affect the intervening medium

Does not affect the intervening medium

4

Absorptive power

Emissive power

Emissivity

None of these