4

0.1

0.3

0.7

1.7

C. 0.7

4

# A steam pipe is to be insulated by two insulating materials put over each other. For best results

Better insulation should be put over pipe and better one over it

Inferior insulation should be put over pipe and better one over it

Both may be put in any order

Whether to put inferior OIL over pipe or the better one would depend on steam temperature

4

Glass

Water

Plastic

Air

4

# Fourier's law of heat conduction is valid for

One dimensional cases only

Two dimensional cases only

Three dimensional cases only

Regular surfaces having non-uniform temperature gradients

4

-1/3

-2/3

1

-1

4

One

Two

Three

Four

4

# Reynolds number is the ratio of

Energy transferred by convection to that by conduction

Kinematic viscosity to thermal diffusivity

Inertia force to viscous force

None of the above

4

Grashoff number

Nusselt number

Weber number

Prandtl number

4

# The expression Q = ρ AT4 is called

Fourier equation

Stefan-Boltzmann equation

Newton Reichmann equation

Joseph-Stefan equation

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

# 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

h = k/ ρS

h = ρS/k

h = S/ρk

h = kρ/S

4

# When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by

Conduction

Convection

Conduction and convection

4

# Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium.

Cold body to hot body

Hot body to cold body

Smaller body to larger body

Larger body to smaller body

4

All of these

4

Stanton number

Biot number

Peclet number

Grashoff number

4

W/m²K

W/m²

W/mK

W/m

4

# Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in

Electric heater

Steam condenser

Boiler

Refrigerator condenser coils

4

Iron

Concrete

Wood

4

K cal/kg m² °C

K cal m/hr m² °C

K cal/hr m² °C

K calm/hr °C

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

Conduction

Convection

None of these

4

# Depending on the radiating properties, body will be transparent when

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

4

Temperature

Thickness

Area

Time

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

# The critical temperature is the temperature

Below which a gas does not obey gas laws

Above which a gas may explode

Below which a gas is always liquefied

Above which a gas will never liquefied

4

Black body

Grey body

Opaque body

White body

4

0.45

0.55

0.40

0.75

4

# The thermal diffusivities for solids are generally

Less than those for gases

Less than those for liquids

More than those for liquids and gases

More or less same as for liquids and gases

4

Grashoff number

Biot number

Stanton number

Prandtl number