Energy emitted by all bodies; Stefan-Boltzmann law q=εσT⁴.
All bodies emit thermal radiation; blackbody emissive power E_b=σT⁴ (σ=5.67×10⁻⁸). Real surfaces have emissivity ε. Net exchange Q=εσA(T₁⁴-T₂⁴). Wavelength distribution follows Planck; Wien's law λ_max=2898/T µm. Dominates at high temperature and in vacuum.
A 1 m² surface at 500 K with ε=0.8 emits about 2.8 kW.
Radiation transfers heat across vacuums and between surfaces, which matters for furnaces, spacecraft and high-temperature components.
Energy emitted by all bodies; Stefan-Boltzmann law q=εσT⁴.
Radiation transfers heat across vacuums and between surfaces, which matters for furnaces, spacecraft and high-temperature components.
It gives the total power radiated by a surface as emissivity times the Stefan-Boltzmann constant times absolute temperature to the fourth power.
Emissivity sets how well a surface radiates, so polished metals radiate less than black surfaces at the same temperature.
Typical applications include calculating the heat loss from a hot furnace wall to its surroundings, designing a spacecraft thermal control surface and estimating radiative heat transfer between two hot pipes in a plant.
Study "Nusselt number" first (topic 88 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
Absorptivity, reflectivity, transmissivity. Kirchhoff's law. Greenhouse effect.
A 1 m² surface at 500 K with ε=0.8 emits about 2.8 kW.
The next topic is "View factors", which builds directly on this one.
It is classed as Advanced in Thermodynamics & Fluids (topic 89 of 105). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Thermodynamics & Fluids.
Want to practise? Open the interactive course for quick checks, quizzes, simulations and progress tracking.