Radiation
Four modes: E_b = σT⁴, irradiation G = Φ/A with absorbed flux αG, two-surface gray exchange Q = σ(T₁⁴−T₂⁴)/[(1−ε₁)/A₁ε₁ + 1/A₁F₁₂ + (1−ε₂)/A₂ε₂], and identical-shield parallel plates Q = Aεσ(T₁⁴−T₂⁴)/(N+1).
Mode
Surface
Two-surface
Frequently asked
- What are the surface and space resistances?
- A gray surface contributes (1−ε)/(Aε) — the bigger the emissivity shortfall, the bigger the resistance. The gap between surfaces contributes 1/(A₁F₁₂), set purely by geometry through the view factor.
- How much does one radiation shield help?
- One shield between large parallel plates halves the exchange; N identical shields divide it by N+1. That is why thermos bottles and cryogenic dewars use many reflective layers.
- When is the small-object formula enough?
- When a small object (area A₁) sits inside a much larger enclosure, Q = ε₁A₁σ(T₁⁴−T₂⁴) — the enclosure's emissivity and shape stop mattering.