Radiation

Question 1

What is absorptivity?

Answer 1

is the fraction of energy absorbed.

Question 2

What is reflectivity?

Answer 2

is the fraction of energy reflected.

Question 3

What is transmissivity?

Answer 3

is the fraction of energy transmitted.

Question 4

What is the radiation conservation law?

Answer 4

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.

Question 5

What is the radiation conservation law equal to?

Answer 5

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

Question 6

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

Answer 6

For an opaque body, transmissivity is zero.

Question 7

What is emissivity?

Answer 7

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

Question 8

What is Kirchhoff’s radiation law?

Answer 8

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.

Question 9

What are gray bodies?

Answer 9

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

Question 10

What are real bodies?

Answer 10

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

Question 11

What are black bodies?

Answer 11

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

Question 12

What is the Stephan Boltzmann law?

Answer 12

The energy radiated from a body.

Question 13

What is Stephan Boltzmann law dependent on?

Answer 13

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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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

Question 16

What is the shape factor?

Answer 16

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

Question 17

What is the shape factor range?

Answer 17

Its range is from zero to one.

Question 18

What is the reprocity theorem?

Answer 18

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.

Question 19

What is the view conservation rule?

Answer 19

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.

Question 20

What is the view conservation rule equal to?

Answer 20

The sum of the shape factors is equal to 1.

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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

Question 23

What is two surface enclosure?

Answer 23

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.

Question 24

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

Answer 24

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

Question 25

What shapes are sufficiently convex in two surface enclosure?

Answer 25

Parallel plates, concentric cylinders, and concentric spheres

Question 26

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

Answer 26

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

Question 27

What are refractory materials or refractories?

Answer 27

Surfaces that reradiate absorbed thermal radiation.