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4

# An ordinary passenger aircraft requires a cooling system of capacity.

2 TR

4 TR

8 TR

10 TR

C. 8 TR

### Related Questions

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4

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

Blast furnace

Heating of building

Cooling of parts in furnace

Heat received by a person from fireplace

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4

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

Q = 2πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 4πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 6πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 8πkr1 r2 (T1 - T2)/ (r2 - r1)

What is the correct answer?

4

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

Conduction

Convection

Radiation

Conduction and convection

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4

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

Increases

Decreases

Remain constant

May increase or decrease depending on temperature

What is the correct answer?

4

# According to Wien's law, the wavelength corresponding to maximum energy is proportion to

Absolute temperature (T)

F

T

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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

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4

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

Stanton number

Nusselt number

Biot number

Peclet number

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4

# When heat is transferred by molecular collision, it is referred to as heat transfer by

Conduction

Convection

Radiation

Scattering

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4

# Thermal conductivity of water in general with rise in temperature

Increases

Decreases

Remain constant

May increase or decrease depending on temperature

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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

Conduction

Free convection

Forced convection

Radiation

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4

# Thermal conductivity of a material may be defined as the

Quantity of heat flowing in one second through one cm cube of material when opposite faces ^re maintained at a temperature difference of 1°C

Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C

Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces

All of the above

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4

# Thermal diffusivity of a substance is

Directly proportional to the thermal conductivity

Inversely proportional to density of substance

Inversely proportional to specific heat

All of the above

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4

# The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to

Stanton number

Biot number

Peclet number

Grashoff number

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4

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

α = 1, ρ = 0 and τ = 0

α = 0, ρ = 1 and τ = 0

α = 0, ρ = 0 and τ = 1

α + ρ = 1 and τ = 0

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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 Stefan Boltzmann constant is

Watt/cm² °K

Watt/cm4 °K

Watt²/cm °K⁴

Watt/cm² °K⁴

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4

# When absorptivity (α) = 1, reflectivity (ρ) = 0 and transmissivity (τ) = 0, then the body is said to be a

Black body

Grey body

Opaque body

White body

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4

# Absorptivity of a body will be equal to its emissivity

At all temperatures

At one particular temperature

When system is under thermal equilibrium

At critical temperature

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4

# If the energy radiated per second per sq. cm. of the surface for wave lengths lying between λ, and λ + dλ is represented by (eλ.dλ), then eλ is called

Absorptive power

Emissive power

Emissivity

None of these

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4

# According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a

Grey body

Brilliant white polished body

Red hot body

Black body

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4

# The heat of sun reaches to us according to

Conduction

Convection

Radiation

None of these

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4

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

Grashoff number

Nusselt number

Weber number

Prandtl number

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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

# A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is

h₁ + h₂ + h₃

(h₁.h₂.h₃)1/3

1/h₁ + 1/h₂ + 1/h₃

None of these

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4

# The critical thickness of insulation for a sphere is

k/h₀

2k/h₀

h₀/k

h₀/2k

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4

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

0.002

0.02

0.01

0.1

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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

# The highest thermal diffusivity is of

Iron

Lead

Concrete

Wood

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4

# Which of the following property of air does not increase with rise in temperature?

Thermal conductivity

Thermal diffusivity

Density

Dynamic viscosity

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4

# Metals are good conductors of heat because

Their atoms collide frequently

Their atoms are relatively far apart

They contain free electrons

They have high density