Radiation

Question 1

Equation for resistance (rad)

Answer 1

R(rad) = 1 / (h(rad) * As)

Question 2

Electromagnetic radiation energy, e =

Answer 2

e = hv = hc/λ

h = planks constant = 6.62 * 10^(-34)

Question 3

Absorptivity

Answer 3

absorbed radiation
α = —————————
incident radiation

Question 4

Reflectivity

Answer 4

reflected radiation
ρ = —————————
incident radiation

Question 5

Transmissivity

Answer 5

transmitted radiation
τ = —————————–
incident radiation
(transmitted radiation is radiation that goes through material completely)

Question 6

Equation linking absorptivity, reflectivity, transmissivity

Answer 6

α + ρ+ τ = 1

Question 7

Definition of a Blackbody

Answer 7

• A blackbody emits the maximum amount of radiation by a surface at a given temperature
• perfect emitter and absorber of radiation

Question 8

Equation for energy emitted from a black body

Answer 8

E(bτ) = σT^4

where
σ = Stefan-Boltzmann constant = 5.67 x 10^(-8)

Question 9

Definition of radiosity, J

Answer 9

radiosity = reflected irradiation + emitted radiation

for diffuse emitter and reflector:
J = πl(e+r)
for black body
J = E(b)

Question 10

Definition of emissivity

Answer 10

Definition:
Ratio of the total radiation energy emitted by the surface to the radiation emitted by a black body of the same temperature

ε = E(τ) / E(b)

Question 11

Define view factor

Answer 11

F(i,j) = Fraction of energy leaving i that strikes surface j directly

Question 12

View factor, summation rule

Answer 12

ΣF(i,j) = 1

pg.54 LBOTF

Question 13

View factor, reciprocity relation

Answer 13

A(i)*F(i,j) = A(j)F(j,i)

pg.54 LBOTF?

Question 14

Limits to use of view factors

Answer 14

Only usable if:

• source is uniform in all directions (diffuse)
• medium between surfaces does not absorb, emit or scatter radiation

Question 15

Definition of diffuse

Answer 15

Source is uniform in all directions

Question 16

Equation for radiation form blackbodies using view factor

Answer 16

R(i,j) = 1 / ( A(i)F(i,j) )

like a resistance term

Question 17

Equation for surface resistance (radiation)

Answer 17

R(i) = (1-εi) / ( A(i)E(i) )

note: if εi = 1, then calculation for blackbody

Question 18

Equation for space resistance (radiation)

Answer 18

Q(i,j) = (J(i) - J(j)) / ( A(i) * F(i,j) )

J = radiosity
pg. 54 LBOTF

Question 19

Equation for two surface radiation problem. Can be found on which page of LBOTF

Answer 19

pg. 52

Qij = σ(T1^4 - T2^4) / (R1 + R12 + R2)

Where R = resistance terms