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

C. One dimensional cases only

4

One

Two

Three

Four

4

Free convection flow depends on

Density

Coefficient of viscosity

Gravitational force

All of these

4

Thermometer

Thermistor

Thermocouple

None of these

4

The energy distribution of an ideal reflector at higher temperatures is largely in the range of

Shorter wavelength

Longer wavelength

Remain same at all wavelengths

Wavelength has nothing to do with it

4

Planck's law holds good for

Black bodies

Polished bodies

All coloured bodies

All of the above

4

kcal/m²

kcal/hr °C

kcal/m² hr °C

kcal/m hr °C

4

2 TR

4 TR

8 TR

10 TR

4

Heat transfer in liquid and gases takes place by

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

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

Conduction

Convection

Conduction and convection

4

Thermal conductivity of air with rise in temperature

Increases

Decreases

Remain constant

May increase or decrease depending on temperature

4

In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by

Convection

Conduction

Both convection and conduction

4

The thermal diffusivities for gases are generally

More than those for liquids

Less than those for liquids

More than those for solids

Dependent on the viscosity

4

1 : 1

2 : 1

1 : 2

4 : 1

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

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

Electric heater

Steam condenser

Boiler

Refrigerator condenser coils

4

0.1

0.3

0.7

1.7

4

Moisture

Density

Temperature

All of the above

4

Absorptive power

Emissive power

Emissivity

None of these

4

Film coefficient is defined as Inside diameter of tube

Equivalent thickness of film

Thermal conductivity Equivalent thickness of film Specific heat × Viscosity

Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity

Film coefficient × Inside diameter Thermal conductivity

4

The amount of radiation mainly depends on

Nature of body

Temperature of body

Type of surface of body

All of the above

4

-1/3

-2/3

1

-1

4

Stanton number

Nusselt number

Biot number

Peclet number

4

A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,

The better insulation must be put inside

The better insulation must be put outside

One could place either insulation on either side

One should take into account the steam temperature before deciding as to which insulation is put where

4

Conduction

Convection

None of these

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 total radiation from a black body per second per unit area is ________ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.

Equal to

Directly proportional to

Inversely proportional to

None 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

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