4

Conduction

Convection

None of these

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

Temperature

Thickness

Area

Time

4

Moisture

Density

Temperature

All of the above

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

Liquids

Energy

Temperature

Entropy

4

Maximum

Minimum

Zero

None of these

4

# Thermal conductivity of water ________ with rise in temperature.

Remain same

Decreases

Increases

May increase or decrease depending upon temperature

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

# 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

# The natural convection air cooled condensers are used in

Domestic refrigerators

Water coolers

Room air conditioners

All of these

4

# Which of the following is the case of heat transfer by radiation?

Blast furnace

Heating of building

Cooling of parts in furnace

Heat received by a person from fireplace

4

Conduction

Convection

None of these

4

# The rate of heat flow through a body is Q = [kA (T₁ - T₂)]/x. The term x/kA is known as

Thermal coefficient

Thermal resistance

Thermal conductivity

None of these

4

1 : 1

2 : 1

1 : 2

4 : 1

4

# The most commonly used method for the design of duct size is the

Velocity reduction method

Equal friction method

Static regains method

Dual or double method

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

# Fourier's law of heat conduction is valid for

One dimensional cases only

Two dimensional cases only

Three dimensional cases only

Regular surfaces having non-uniform temperature gradients

4

# Free convection flow depends on

Density

Coefficient of viscosity

Gravitational force

All of these

4

RN = hl/k

RN = μ cp/k

RN = ρ V l /μ

RN = V²/t.cp

4

0.1

0.23

0.42

0.51

4

Iron

Concrete

Wood

4

# Absorptivity of a body will be equal to its emissivity

At all temperatures

At one particular temperature

When system is under thermal equilibrium

At critical temperature

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

# According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

Absolute temperature

Square of the absolute temperature

Cube of the absolute temperature

Fourth power of the absolute temperature

4

# The automobile radiator is a heat exchanger of

Parallel flow type

Counter flow type

Cross flow type

Regenerator type

4

# The amount of radiation mainly depends on

Nature of body

Temperature of body

Type of surface of body

All of the above

4

Watt/mK

Watt/m²K²

Watt/m²K4

Watt/mK²

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

All of these