4

# The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called

First law of thermodynamics

Newton's law of cooling

Newton's law of heating

Stefan's law

B. Newton's law of cooling

4

# Unit of thermal conductivity in S.I. units is

J/m² sec

J/m °K sec

W/m °K

Option (B) and (C) above

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

# 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

Thermometer

Thermistor

Thermocouple

None of these

4

W/m²K

W/m²

W/mK

W/m

4

Conduction

Convection

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

# 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

# The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called

First law of thermodynamics

Newton's law of cooling

Newton's law of heating

Stefan's law

4

# According of Kirchhoff's law

Radiant heat is proportional to fourth power of absolute temperature

Emissive power depends on temperature

Emissive power and absorptivity are constant for all bodies

Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body.

4

m²/hr

m²/hr °C

kcal/m² hr

kcal/m. hr °C

4

RN = hl/k

RN = μ cp/k

RN = ρ V l /μ

RN = V²/t.cp

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

4

# The insulation ability of an insulator with the presence of moisture would

Increase

Decrease

Remain unaffected

May increase/decrease depending on temperature and thickness of insulation

4

Wien's law

Stefan's law

Kirchhoff's law

Planck's law

4

# The heat transfer by conduction through a thick cylinder (Q) is given by (where T₁ = Higher temperature, T₂ = Lower temperature, r₁ = Inside radius, r₂ = Outside radius, l = Length of cylinder, and k = Thermal conductivity)

Q = [2πlk (T₁ - T₂)]/2.3 log (r₂/r₁)

Q = 2.3 log (r₂/r₁)/[2πlk (T₁ - T₂)]

Q = [2π (T₁ - T₂)]/2.3 lk log (r₂/r₁)

Q = = 2πlk/2.3 (T₁ - T₂) log (r₂/r₁)

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

# The heat transfer takes place according to

Zeroth law of thermodynamics

First law of thermodynamics

Second law of thermodynamics

Kirchhoff's law

4

Temperature

Thickness

Area

Time

4

# A perfect black body is one which

Is black in colour

Reflects all heat

Absorbs heat radiations of all wave lengths falling on it

4

# Planck's law holds good for

Black bodies

Polished bodies

All coloured bodies

All of the above

4

Minimum energy

Maximum energy

Both (A) and (B)

None of these

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

# 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

Glass

Water

Plastic

Air

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

# Which of the following property of air does not increase with rise in temperature?

Thermal conductivity

Thermal diffusivity

Density

Dynamic viscosity

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

# The natural convection air cooled condensers are used in

Domestic refrigerators

Water coolers

Room air conditioners

All of these