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According to Prevost theory of heat exchange

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

B. Heat transfer by radiation requires no medium

C. All bodies above absolute zero emit radiation

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

Correct Answer :

C. All bodies above absolute zero emit radiation


Related Questions

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Which of the following has least value of conductivity?

A. Glass

B. Water

C. Plastic

D. Air

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4

Sensible heat is the heat required to

A. Change vapour into liquid

B. Change liquid into vapour

C. Increase the temperature of a liquid of vapour

D. Convert water into steam and superheat it

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4

Absorptivity of a body will be equal to its emissivity

A. At all temperatures

B. At one particular temperature

C. When system is under thermal equilibrium

D. At critical temperature

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4

The thermal diffusivities for gases are generally

A. More than those for liquids

B. Less than those for liquids

C. More than those for solids

D. Dependent on the viscosity

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Unit of thermal conductivity in S.I. units is

A. J/m² sec

B. J/m °K sec

C. W/m °K

D. Option (B) and (C) above

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4

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

A. Conduction

B. Convection

C. Radiation

D. Conduction and convection

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4

In heat exchangers, degree of approach is defined as the difference between temperatures of

A. Cold water inlet and outlet

B. Hot medium inlet and outlet

C. Hot medium outlet and cold water inlet

D. Hot medium outlet and cold water outlet

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4

Heat is closely related with

A. Liquids

B. Energy

C. Temperature

D. Entropy

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4

Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ρ = Density of substance, S = Specific heat, and k = Thermal conductivity)

A. h = k/ ρS

B. h = ρS/k

C. h = S/ρk

D. h = kρ/S

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4

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

A. Minimum energy

B. Maximum energy

C. Both (A) and (B)

D. None of these

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4

The thermal diffusivities for solids are generally

A. Less than those for gases

B. Less than those for liquids

C. More than those for liquids and gases

D. More or less same as for liquids and gases

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4

Sensible heat factor is given by (where S.H. = Sensible heat, and L.H. = Latent heat)

A. S.H/(S.H + L.H)

B. (S.H + L.H) /S.H

C. (L.H - S.H)/S.H

D. S.H/(L.H - S.H)

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The ratio of the energy absorbed by the body to total energy falling on it is called

A. Absorptive power

B. Emissive power

C. Absorptivity

D. Emissivity

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The amount of radiation mainly depends upon the

A. Nature of the body

B. Temperature of the body

C. Type of surface of the body

D. All of these

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4

Which of the following has maximum value of thermal conductivity?

A. Aluminium

B. Steel

C. Brass

D. Copper

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4

Fourier's law of heat conduction gives the heat flow for

A. Irregular surfaces

B. Nonuniform temperature surfaces

C. One dimensional cases only

D. Two dimensional cases only

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

A. Stanton number

B. Nusselt number

C. Biot number

D. Peclet number

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In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the

A. Reynold's number

B. Grashoff's number

C. Reynold's number, Grashoff's number

D. Prandtl number, Grashoff's number

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4

Depending on the radiating properties, a body will be black when

A. P = 0, x = 0 and a = 1

B. P= 1, T = 0 and a = 0

C. P = 0, x = 1 and a = 0

D. X = 0, a + p = 0 Where a = absorptivity, p = reflectivity, X = transmissivity.

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Emissivity of a white polished body in comparison to a black body is

A. Higher

B. Lower

C. Same

D. Depends upon the shape of body

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The expression Q = ρ AT4 is called

A. Fourier equation

B. Stefan-Boltzmann equation

C. Newton Reichmann equation

D. Joseph-Stefan equation

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All radiations in a black body are

A. Reflected

B. Refracted

C. Transmitted

D. Absorbed

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4

Thermal conductivity of air with rise in temperature

A. Increases

B. Decreases

C. Remain constant

D. May increase or decrease depending on temperature

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The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles caused by some mechanical means, is known as

A. Conduction

B. Free convection

C. Forced convection

D. Radiation

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Thermal conductivity of water ________ with rise in temperature.

A. Remain same

B. Decreases

C. Increases

D. May increase or decrease depending upon temperature

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4

A grey body is one whose absorptivity

A. Varies with temperature

B. Varies with wavelength of the incident ray

C. Is equal to its emissivity

D. Does not vary with temperature and. wavelength of the incident ray

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4

Which of the following would lead to a reduction in thermal resistance?

A. In conduction, reduction in the thickness of the material and an increase in thermal conductivity.

B. In convection, stirring of the fluid and cleaning the heating surface.

C. In radiation, increasing the temperature and reducing the emissivity.

D. All of the above

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The natural convection air cooled condensers are used in

A. Domestic refrigerators

B. Water coolers

C. Room air conditioners

D. All of these

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4

The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as

A. Kirchoffs law

B. Stefan's law

C. Wien' law

D. Planck's law

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According to Stefan's law, the total radiation from a black body per second per unit area is proportional to

A. Absolute temperature

B.

C. T⁵

D. T