4

Thermometer

Thermistor

Thermocouple

None of these

C. Thermocouple

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

Kirchhoff's law

Stefan's law

Wines law

Planck's law

4

h = k/ ρS

h = ρS/k

h = S/ρk

h = kρ/S

4

The time constant of a thermocouple is

The time taken to attain the final temperature to be measured

The time taken to attain 50% of the value of initial temperature difference

The time taken to attain 63.2% of the value of initial temperature difference

Determined by the time taken to reach 100°C from 0°C

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 transfer by radiation mainly depends upon

Its temperature

Nature of the body

Kind and extent of its surface

All of the above

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

Hr (time)

Sq. m (area)

°C (temperature)

K.cal (heat)

4

Conduction

Convection

Scattering

4

Moisture

Density

Temperature

All of the above

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

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

Conduction

Convection

Conduction and convection

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

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

20°C

40°C

60°C

66.7°C

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

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

Thermometer

Thermistor

Thermocouple

None of these

4

Free convection flow depends on

Density

Coefficient of viscosity

Gravitational force

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

RN = hl/k

RN = μ cp/k

RN = ρ V l /μ

RN = V²/t.cp

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

k. A. (dT/dx)

k. A. (dx/dT)

k. (dT/dx)

k. (dx/dT)

4

1 : 1

2 : 1

1 : 2

4 : 1

4

25 mm

40 mm

160 mm

800 mm

4

Joule sec is the unit of

Universal gas constant

Kinematic viscosity

Thermal conductivity

Planck's constant

4

Absorptive power

Emissive power

Emissivity

None of these

4

Stanton number

Biot number

Peclet number

Grashoff number

4

Watt/mK

Watt/m²K²

Watt/m²K4

Watt/mK²