Radiation Flashcards
Equation for resistance (rad)
R(rad) = 1 / (h(rad) * As)
Electromagnetic radiation energy, e =
e = hv = hc/λ
h = planks constant = 6.62 * 10^(-34)
Absorptivity
absorbed radiation
α = —————————
incident radiation
Reflectivity
reflected radiation
ρ = —————————
incident radiation
Transmissivity
transmitted radiation
τ = —————————–
incident radiation
(transmitted radiation is radiation that goes through material completely)
Equation linking absorptivity, reflectivity, transmissivity
α + ρ+ τ = 1
Definition of a Blackbody
- A blackbody emits the maximum amount of radiation by a surface at a given temperature
- perfect emitter and absorber of radiation
Equation for energy emitted from a black body
E(bτ) = σT^4
where
σ = Stefan-Boltzmann constant = 5.67 x 10^(-8)
Definition of radiosity, J
radiosity = reflected irradiation + emitted radiation
for diffuse emitter and reflector:
J = πl(e+r)
for black body
J = E(b)
Definition of emissivity
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)
Define view factor
F(i,j) = Fraction of energy leaving i that strikes surface j directly
View factor, summation rule
ΣF(i,j) = 1
pg.54 LBOTF
View factor, reciprocity relation
A(i)*F(i,j) = A(j)F(j,i)
pg.54 LBOTF?
Limits to use of view factors
Only usable if:
- source is uniform in all directions (diffuse)
- medium between surfaces does not absorb, emit or scatter radiation
Definition of diffuse
Source is uniform in all directions
Equation for radiation form blackbodies using view factor
R(i,j) = 1 / ( A(i)F(i,j) )
like a resistance term
Equation for surface resistance (radiation)
R(i) = (1-εi) / ( A(i)E(i) )
note: if εi = 1, then calculation for blackbody
Equation for space resistance (radiation)
Q(i,j) = (J(i) - J(j)) / ( A(i) * F(i,j) )
J = radiosity
pg. 54 LBOTF
Equation for two surface radiation problem. Can be found on which page of LBOTF
pg. 52
Qij = σ(T1^4 - T2^4) / (R1 + R12 + R2)
Where R = resistance terms
