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What is the correct answer?

4

Upto the critical radius of insulation,

A. Added insulation will increase heat loss

B. Added insulation will decrease heat loss

C. Convective heat loss will be less than conductive heat loss

D. Heat flux will decrease

Correct Answer :

A. Added insulation will increase heat loss


Related Questions

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4

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

A. Increase

B. Decrease

C. Remain unaffected

D. May increase/decrease depending on temperature and thickness of insulation

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4

The automobile radiator is a heat exchanger of

A. Parallel flow type

B. Counter flow type

C. Cross flow type

D. Regenerator type

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4

Fourier's law of heat conduction is valid for

A. One dimensional cases only

B. Two dimensional cases only

C. Three dimensional cases only

D. Regular surfaces having non-uniform temperature gradients

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4

The unit of Stefan-Boltzmann constant is

A. Watt/mK

B. Watt/m²K²

C. Watt/m²K4

D. Watt/mK²

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4

The critical thickness of insulation for a sphere is

A. k/h₀

B. 2k/h₀

C. h₀/k

D. h₀/2k

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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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4

Unit of thermal conductivity in M.K.S. units is

A. K cal/kg m² °C

B. K cal m/hr m² °C

C. K cal/hr m² °C

D. K calm/hr °C

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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

The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit

A. Temperature

B. Thickness

C. Area

D. Time

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The critical radius is the insulation radius at which the resistance to heat flow is

A. Maximum

B. Minimum

C. Zero

D. None 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

A grey body is one whose absorptivity

A. Varies with temperature

B. Varies with the wave length of incident ray

C. Varies with both

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

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4

In free convection heat transfer, Nusselt number is function of

A. Grashoff number and Reynold number

B. Grashoff number and Prandtl number

C. Prandtl number and Reynold number

D. Grashoff number, Prandtl number and Reynold number

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4

Thermal conductivity of non-metallic amorphous solids with decrease in temperature

A. Increases

B. Decreases

C. Remain constant

D. May increase or decrease depending on temperature

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4

Total emissivity of polished silver compared to black body is

A. Same

B. Higher

C. More or less same

D. Very much lower

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4

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

Heat transfer by radiation mainly depends upon

A. Its temperature

B. Nature of the body

C. Kind and extent of its surface

D. All of the above

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Heat transfer takes place as per

A. Zeroth law of thermodynamics

B. First law of thermodynamic

C. Second law of the thermodynamics

D. Kirchoff's law

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4

The radiation emitted by a black body is known as

A. Black radiation

B. Full radiation

C. Total radiation

D. All of these

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4

The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is

A. Equal to one

B. Greater than one

C. Less than one

D. Equal to Nusselt number

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4

The amount of radiation mainly depends on

A. Nature of body

B. Temperature of body

C. Type of surface of body

D. All of the above

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4

Upto the critical radius of insulation,

A. Added insulation will increase heat loss

B. Added insulation will decrease heat loss

C. Convective heat loss will be less than conductive heat loss

D. Heat flux will decrease

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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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4

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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4

Thermal conductivity of water at 20°C is of the order of

A. 0.1

B. 0.23

C. 0.42

D. 0.51

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4

The value of the wave length for maximum emissive power is given by

A. Kirchhoff's law

B. Stefan's law

C. Wines law

D. Planck's law

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4

Unit of thermal diffusivity is

A. m²/hr

B. m²/hr °C

C. kcal/m² hr

D. kcal/m. hr °C

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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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4

Thermal conductivity of solid metals with rise in temperature normally

A. Increases

B. Decreases

C. Remain constant

D. May increase or decrease depending on temperature

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4

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