What is the correct answer?

4

# The amount of radiation mainly depends upon the

Nature of the body

Temperature of the body

Type of surface of the body

All of these

D. All of these

### Related Questions

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4

# Fourier's law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow, and k = Thermal conductivity of the body)

k. A. (dT/dx)

k. A. (dx/dT)

k. (dT/dx)

k. (dx/dT)

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4

# Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be

One

Two

Three

Four

What is the correct answer?

4

# The heat is transferred by conduction, convection and radiation in

Melting of ice

Boiler furnaces

Condensation of steam in condenser

None of these

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4

# According to Dalton's law of partial pressures, (where pb = Barometric pressure, pa = Partial pressure of dry air, and pv = Partial pressure of water vapour)

Pb = pa - pv

Pb = pa + pv

Pb = pa × pv

Pb = pa/pv

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4

# A perfect black body is one which

Is black in colour

Reflects all heat

Transmits all heat radiations

Absorbs heat radiations of all wave lengths falling on it

What is the correct answer?

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

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4

# An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be

25 mm

40 mm

160 mm

800 mm

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4

# The highest thermal diffusivity is of

Iron

Lead

Concrete

Wood

What is the correct answer?

4

# Wiens law states that the wave length corresponding to ________ is proportional to the absolute temperature.

Minimum energy

Maximum energy

Both (A) and (B)

None of these

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4

# The transfer of heat by molecular collision is smallest in

Solids

Liquids

Gases

None of these

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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

What is the correct answer?

4

# The expression Q = ρ AT4 is called

Fourier equation

Stefan-Boltzmann equation

Newton Reichmann equation

Joseph-Stefan equation

What is the correct answer?

4

# In free convection heat transfer, Nusselt number is function of

Grashoff number and Reynold number

Grashoff number and Prandtl number

Prandtl number and Reynold number

Grashoff number, Prandtl number and Reynold number

What is the correct answer?

4

# Heat is closely related with

Liquids

Energy

Temperature

Entropy

What is the correct answer?

4

# According to Prevost theory of heat exchange

It is impossible to transfer heat from low temperature source to t high temperature source

Heat transfer by radiation requires no medium

All bodies above absolute zero emit radiation

Heat transfer in most of the cases takes place by combination of conduction, convection and radiation

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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

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4

# The unit of overall coefficient of heat transfer is

W/m²K

W/m²

W/mK

W/m

What is the correct answer?

4

# The emissive power of a body depends upon its

Temperature

Wave length

Physical nature

All of the above

What is the correct answer?

4

# The rate of energy transferred by convection to that by conduction is called

Stanton number

Nusselt number

Biot number

Peclet number

What is the correct answer?

4

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

Convection

Radiation

Forced convection

Free convection

What is the correct answer?

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

What is the correct answer?

4

# The unit of overall coefficient of heat transfer is

kcal/m²

kcal/hr °C

kcal/m² hr °C

kcal/m hr °C

What is the correct answer?

4

# Fouling factor is used

In heat exchanger design as a safety factor

In case of Newtonian fluids

When a liquid exchanges heat with a gas

None of the above

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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.

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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

What is the correct answer?

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

What is the correct answer?

4

# Temperature of steam at around 540°C can be measured by

Thermometer

Thermistor

Thermocouple

None of these

What is the correct answer?

4

# The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles due to difference of density caused by temperature of the particle is known as

Conduction

Free convection

Forced convection

Radiation

What is the correct answer?

4

# Heat transfer in liquid and gases takes place by

Conduction

Convection

Radiation

Conduction and convection

What is the correct answer?

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