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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

Correct Answer :

D. May increase or decrease depending upon temperature


Related Questions

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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.

A. Equal to

B. Directly proportional to

C. Inversely proportional to

D. None of these

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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

A. Convection

B. Radiation

C. Conduction

D. Both convection and conduction

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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

A. Conduction

B. Convection

C. Radiation

D. Conduction and convection

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Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of

A. 0.002

B. 0.02

C. 0.01

D. 0.1

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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 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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Kirchhoff's law states that

A. The total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature

B. The wave length corresponding to the maximum energy is proportional to the absolute temperature

C. 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

D. None of the above

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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

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The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as

A. Emissivity

B. Transmissivity

C. Reflectivity

D. Intensity of radiation

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If the temperature of a solid surface changes from 27°C to 627°C, then its emissive power changes in the ratio of

A. 6

B. 9

C. 27

D. 81

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The process of heat transfer from one particle of the body to another by the actual motion of the heated particles, is called

A. Conduction

B. Convection

C. Radiation

D. None of these

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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 unit of overall coefficient of heat transfer is

A. kcal/m²

B. kcal/hr °C

C. kcal/m² hr °C

D. kcal/m hr °C

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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

Thermal conductivity of glass wool varies from sample to sample because of variation in

A. Composition

B. Density

C. Porosity

D. All of the above

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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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In regenerator type heat exchanger, heat transfer takes place by

A. Direct mixing of hot and cold fluids

B. A complete separation between hot and cold fluids

C. Flow of hot and cold fluids alternately over a surface

D. Generation of heat again and again

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4

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

A. The better insulation must be put inside

B. The better insulation must be put outside

C. One could place either insulation on either side

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

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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

A. Conduction

B. Free convection

C. Forced convection

D. Radiation

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The heat transfer takes place according to

A. Zeroth law of thermodynamics

B. First law of thermodynamics

C. Second law of thermodynamics

D. Kirchhoff's law

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Which of the following is a case of steady state heat transfer?

A. I.C. engine

B. Air preheaters

C. Heating of building in winter

D. None of the above

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

A. Blast furnace

B. Heating of building

C. Cooling of parts in furnace

D. Heat received by a person from fireplace

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Fouling factor is used

A. In heat exchanger design as a safety factor

B. In case of Newtonian fluids

C. When a liquid exchanges heat with a gas

D. None of the above

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

A. Electric heater

B. Steam condenser

C. Boiler

D. Refrigerator condenser coils

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The time constant of a thermocouple is

A. The time taken to attain the final temperature to be measured

B. The time taken to attain 50% of the value of initial temperature difference

C. The time taken to attain 63.2% of the value of initial temperature difference

D. Determined by the time taken to reach 100°C from 0°C

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The product of Reynolds number and Prandtl number is known as

A. Stanton number

B. Biot number

C. Peclet number

D. Grashoff number

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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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Depending on the radiating properties, a body will be white 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 = 1 Where a = absorptivity, p = reflectivity, x = transmissivity

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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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Heat conducted through per unit area and unit thick face per unit time when temperature difference between opposite faces is unity, is called

A. Thermal resistance

B. Thermal coefficient

C. Temperature gradient

D. Thermal conductivity