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Heat Transfer > Radiation > Flashcards

Radiation Flashcards

1
Q

What is absorptivity?

A

is the fraction of energy absorbed.

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2
Q

What is reflectivity?

A

is the fraction of energy reflected.

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3
Q

What is transmissivity?

A

is the fraction of energy transmitted.

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4
Q

What is the radiation conservation law?

A

A body in the path of thermal radiation energy can absorb the energy, reflect the energy, transmit the energy or a combination of these actions.

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5
Q

What is the radiation conservation law equal to?

A

It is the sum of the absorptivity, reflectivity and the transmissivity which it is always equal to 1.

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6
Q

How is the radiation conservation law affected by an opaque body?

A

For an opaque body, transmissivity is zero.

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7
Q

What is emissivity?

A

The ratio of the actual emitted energy to the ideal emitted power of a body.

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8
Q

What is Kirchhoff’s radiation law?

A

When a body is in thermal equilibrium, the rates of absorbed and transmitted energies must be the same. Making the emissivity of a body equal to its absorptivity.

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9
Q

What are gray bodies?

A

A body that emits at constant emissivity, regardless of wavelength.

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10
Q

What are real bodies?

A

Are bodies that do not radiate at the ideal level. They are frequently approximated as gray bodies.

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11
Q

What are black bodies?

A

Bodies that emit the maximum possible radiation for its temperature and absorb all incident energy.

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12
Q

What is the Stephan Boltzmann law?

A

The energy radiated from a body.

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13
Q

What is Stephan Boltzmann law dependent on?

A

Its dependent on the emissivity, Stefan-Boltzmann constant, surface area, and the temperature of the body.

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14
Q

How is the radiation conservation law effected by a black body?

A

Absorptivity which is equal to one. The emissivity is equal to the absorptivity.

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15
Q

How is the radiation conservation law effected by a gray body?

A

The sum of the reflectivity and the absorptivity is equal to one. The emissivity is equal to the absorptivity.

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16
Q

What is the shape factor?

A

Is the fraction of radiation leaving surface one that is intercepted by surface two.

17
Q

What is the shape factor range?

A

Its range is from zero to one.

18
Q

What is the reprocity theorem?

A

The product of the surface area and the shape factor from object one is equal to the product of the surface area and shape factor of object two.

19
Q

What is the view conservation rule?

A

When a transmitting body is completely surrounded by an N amount of receiving bodies, the total energy intercepted by the receiving bodies will be equal to the transmitted energy.

20
Q

What is the view conservation rule equal to?

A

The sum of the shape factors is equal to 1.

21
Q

What is the net radiation heat transfer for two bodies defined by?

A

Its the Stefan-Boltzmann Law with the temperature being the temperature difference between the two bodies.

22
Q

How is the net heat radiation heat transfer, effected by a small body?

A

If body 1 is small and completely enclosed by body 2, then the shape factor is equal to the emissivity.

23
Q

What is two surface enclosure?

A

Two bodies surfaces, each of which is completely covered enclosed by the other. Although the bodies are completely enclosed, this does not mean that the view factor is equal to 1.

24
Q

When is the shape factor equal to 1 in two surface enclosure?

A

.When there is no shadowing and the enclosure is sufficiently convex.

25
Q

What shapes are sufficiently convex in two surface enclosure?

A

Parallel plates, concentric cylinders, and concentric spheres

26
Q

What is the net radiation heat transfer for diffuse gray surfaces?

A

It is dependent on the Stefan-Boltzmann Law with consideration of the two bodies surface areas and emissivities.

27
Q

What are refractory materials or refractories?

A

Surfaces that reradiate absorbed thermal radiation.

Heat Transfer (3 decks)

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