Thermal Radiation to Large Surroundings

Method & assumptions

1. Net thermal radiation: Q̇ = εσA(Ts⁴ − Tsur⁴). Absolute temperatures must be entered in kelvin.
2. Uses σ = 5.670374419 × 10⁻⁸ W/(m²·K⁴), rounded from the Stefan–Boltzmann constant.
3. Positive heat rate leaves the surface; hotter surroundings produce a negative result. Equal temperatures give zero net exchange.
4. Example: ε = 0.8, A = 1 m², Ts = 400 K and Tsur = 300 K give approximately 793.85 W outward.
5. Model: a gray surface surrounded by a much larger isothermal enclosure, with view factor one and a nonparticipating intervening medium.
6. Does not solve exchange between finite surfaces, solar absorption, semitransparent materials, participating gases or combined convection. Select emissivity for the actual surface condition.

Sources

• OpenStax: Mechanisms of Heat Transfer ↗
• NIST fundamental physical constants ↗