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4

Total heat is the heat required to

A. Change vapour into liquid

B. Change liquid into vapour

C. Increase the temperature of a liquid or vapour

D. Convert water into steam and superheat it

Correct Answer :

D. Convert water into steam and superheat it


Related Questions

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4

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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4

The highest thermal diffusivity is of

A. Iron

B. Lead

C. Concrete

D. Wood

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4

The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body

A. Move actually

B. Do not move actually

C. Affect the intervening medium

D. Does not affect the intervening medium

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4

Metals are good conductors of heat because

A. Their atoms collide frequently

B. Their atoms are relatively far apart

C. They contain free electrons

D. They have high density

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4

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

When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,

A. α = 1, ρ = 0 and τ = 0

B. α = 0, ρ = 1 and τ = 0

C. α = 0, ρ = 0 and τ = 1

D. α + ρ = 1 and τ = 0

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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

Stefan Boltzmann law is applicable for heat transfer by

A. Conduction

B. Convection

C. Radiation

D. Conduction and radiation combined

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4

The unit of Stefan Boltzmann constant is

A. Watt/cm² °K

B. Watt/cm4 °K

C. Watt²/cm °K⁴

D. Watt/cm² °K⁴

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4

A designer chooses the values of fluid flow rates and specific heats in such a manner that the heat capacities of the two fluids are equal. A hot fluid enters the counter flow heat exchanger at 100° C and leaves at 60° C. A cold fluid enters the heat exchanger at 40° C. The mean temperature difference between the two fluids is

A. 20°C

B. 40°C

C. 60°C

D. 66.7°C

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4

The heat transfer by conduction through a thick sphere is given by

A. Q = 2πkr1 r2 (T1 - T2)/ (r2 - r1)

B. Q = 4πkr1 r2 (T1 - T2)/ (r2 - r1)

C. Q = 6πkr1 r2 (T1 - T2)/ (r2 - r1)

D. Q = 8πkr1 r2 (T1 - T2)/ (r2 - r1)

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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

In counter current flow heat exchanger, the logarithmic temperature difference between the fluids is ________ as compared to parallel flow heat exchanger.

A. Same

B. Less

C. Greater

D. None 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

Log mean temperature difference in case of counter flow compared to parallel flow will be

A. Same

B. More

C. Less

D. Depends on other factors

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4

Which of the following has least value of conductivity?

A. Glass

B. Water

C. Plastic

D. Air

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4

The value of Prandtl number for air is about

A. 0.1

B. 0.3

C. 0.7

D. 1.7

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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

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

A non-dimensional number generally associated with natural convection heat transfer is

A. Grashoff number

B. Nusselt number

C. Weber number

D. Prandtl number

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4

Reynolds number (RN) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ρ = Density of fluid, cp = Specific heat at constant pressure, and μ = Coefficient of absolute viscosity)

A. RN = hl/k

B. RN = μ cp/k

C. RN = ρ V l /μ

D. RN = V²/t.cp

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4

In counter flow heat exchangers

A. Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state

B. Both the fluids at inlet are in their hottest state

C. Both the fluids at exit are in their hottest state

D. One fluid is in hottest state and other in coldest state at inlet

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4

The heat of sun reaches to us according to

A. Conduction

B. Convection

C. Radiation

D. None of these

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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

The transfer of heat by molecular collision is smallest in

A. Solids

B. Liquids

C. Gases

D. None of these

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4

Which of the following statement is wrong?

A. The heat transfer in liquid and gases takes place according to convection.

B. The amount of heat flow through a body is dependent upon the material of the body.

C. The thermal conductivity of solid metals increases with rise in temperature

D. Logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference.

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4

Thermal diffusivity of a substance is

A. Directly proportional to the thermal conductivity

B. Inversely proportional to density of substance

C. Inversely proportional to specific heat

D. All of the above

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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

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4

Thermal conductivity of water in general with rise in temperature

A. Increases

B. Decreases

C. Remain constant

D. May increase or decrease depending on temperature

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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