4

Conduction

Convection

None of these

B. Convection

4

Depending on the radiating properties, a body will be black 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 = 0 Where a = absorptivity, p = reflectivity, X = transmissivity.

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

Thermal conductivity of water ________ with rise in temperature.

Remain same

Decreases

Increases

May increase or decrease depending upon temperature

4

Temperature

Thickness

Area

Time

4

Free convection flow depends on

Density

Coefficient of viscosity

Gravitational force

All 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

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

Stanton number

Biot number

Peclet number

Grashoff number

4

Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by

Convection

Forced convection

Free convection

4

The automobile radiator is a heat exchanger of

Parallel flow type

Counter flow type

Cross flow type

Regenerator type

4

Absorptive power

Emissive power

Absorptivity

Emissivity

4

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

Face area

Time

Thickness

Temperature difference

4

0.45

0.55

0.40

0.75

4

Kirchoffs law

Stefan's law

Wien' law

Planck's law

4

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

Absolute temperature (T)

F

T

4

The concept of overall coefficient of heat transfer is used in case of heat transfer by

Conduction

Convection

Conduction and convection

4

Watt/mK

Watt/m²K²

Watt/m²K4

Watt/mK²

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

The logarithmic mean temperature difference (tm) is given by (where Δt1 and Δt2 are temperature differences between the hot and cold fluids at entrance and exit)

tm = (Δt1 - Δt2)/ loge (Δt1/Δt2)

tm = loge (Δt1/Δt2)/ (Δt1 - Δt2)

tm = tm = (Δt1 - Δt2) loge (Δt1/Δt2)

tm = loge (Δt1 - Δt2)/ Δt1/Δt2

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

6

9

27

81

4

k/h₀

2k/h₀

h₀/k

h₀/2k

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

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

Sensible heat is the heat required to

Change vapour into liquid

Change liquid into vapour

Increase the temperature of a liquid of vapour

Convert water into steam and superheat it

4

Hr (time)

Sq. m (area)

°C (temperature)

K.cal (heat)

4

In heat exchangers, degree of approach is defined as the difference between temperatures of

Cold water inlet and outlet

Hot medium inlet and outlet

Hot medium outlet and cold water inlet

Hot medium outlet and cold water outlet