Net Thermal Radiation Calculator
Enter area, temperatures, emissivity and view factor to compute the net radiative heat exchange between two surfaces.
Input Data
Results
At a glance:Net thermal radiation between two surfaces is governed by the Stefan-Boltzmann law. A surface at temperature T emits σ·ε·T⁴ per unit area. The net exchange between a hot surface (T_h) and a colder one (T_c) over area A with emissivity ε and view factor F is Q = ε·σ·A·F·(T_h⁴ − T_c⁴). σ = 5.67×10⁻⁸ W/(m²·K⁴). Emissivity ε ranges from 0 (perfect reflector) to 1 (blackbody); the view factor F accounts for geometric exposure (1 for fully facing surfaces, less otherwise). Because the law depends on T⁴, radiation dominates at high temperatures.
Formula
Net radiation: Q = ε·σ·A·F·(T_h⁴ − T_c⁴)
Stefan-Boltzmann: σ = 5.67×10⁻⁸ W/(m²·K⁴)
$$Q = \sigma \varepsilon A F_{12} (T_h^4 - T_c^4), \quad q = \frac{Q}{A}, \quad h_r = \frac{q}{\Delta T} = \sigma \varepsilon F (T_h^3 + T_h^2 T_c + T_h T_c^2 + T_c^3)$$How to Use
- Enter the area A (m²).
- Enter the hot and cold temperatures (K).
- Enter the emissivity ε and view factor F.
- The calculator returns the net radiated power Q.
Case Studies
Radiator to room
A = 1 m², T_h = 350 K, T_c = 293 K, ε = 0.9, F = 1.
Q ≈ 0.9×5.67e-8×1×1×(350⁴−293⁴) ≈ 300 W.
Most heating felt as radiant warmth.
FAQ
Why does temperature appear to the fourth power?
The Stefan-Boltzmann law states emitted power per area is σ·T⁴, so the net exchange between two bodies carries the difference of fourth powers. This makes radiation overwhelmingly important at high T.
What is a view factor?
The fraction of radiation leaving one surface that reaches the other, from 0 (no line of sight) to 1 (fully facing). It captures geometry of the enclosure.
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References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.