4

Total heat is the heat required to

Change vapour into liquid

Change liquid into vapour

Increase the temperature of a liquid or vapour

Convert water into steam and superheat it

D. Convert water into steam and superheat it

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

4

Iron

Concrete

Wood

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

Metals are good conductors of heat because

Their atoms collide frequently

Their atoms are relatively far apart

They contain free electrons

They have high density

4

Depending on the radiating properties, a body will be white when

P = 0, x = 0 and a = 1

P=1, T = 0 and a = 0

P = 0, x = 1 and a = 0

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

4

When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,

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

4

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

Conduction

Convection

Conduction and convection

4

Conduction

Convection

4

Watt/cm² °K

Watt/cm4 °K

Watt²/cm °K⁴

Watt/cm² °K⁴

4

20°C

40°C

60°C

66.7°C

4

The heat transfer by conduction through a thick sphere is given by

Q = 2πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 4πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 6πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 8πkr1 r2 (T1 - T2)/ (r2 - r1)

4

In free convection heat transfer, Nusselt number is function of

Grashoff number and Reynold number

Grashoff number and Prandtl number

Prandtl number and Reynold number

Grashoff number, Prandtl number and Reynold number

4

Same

Less

Greater

None 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

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

Same

More

Less

Depends on other factors

4

Glass

Water

Plastic

Air

4

0.1

0.3

0.7

1.7

4

In regenerator type heat exchanger, heat transfer takes place by

Direct mixing of hot and cold fluids

A complete separation between hot and cold fluids

Flow of hot and cold fluids alternately over a surface

Generation of heat again and again

4

Thermal conductivity of non-metallic amorphous solids with decrease in temperature

Increases

Decreases

Remain constant

May increase or decrease depending on temperature

4

Grashoff number

Nusselt number

Weber number

Prandtl number

4

RN = hl/k

RN = μ cp/k

RN = ρ V l /μ

RN = V²/t.cp

4

In counter flow heat exchangers

Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state

Both the fluids at inlet are in their hottest state

Both the fluids at exit are in their hottest state

One fluid is in hottest state and other in coldest state at inlet

4

Conduction

Convection

None of these

4

h = k/ ρS

h = ρS/k

h = S/ρk

h = kρ/S

4

Solids

Liquids

Gases

None of these

4

Which of the following statement is wrong?

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.

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

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

Electric heater

Steam condenser

Boiler

Refrigerator condenser coils

4

Thermal conductivity of water in general with rise in temperature

Increases

Decreases

Remain constant

May increase or decrease depending on temperature