Fraction of radiation leaving one surface that strikes another.
F₁₂ is the fraction of radiation leaving surface 1 that reaches surface 2. Reciprocity A₁F₁₂=A₂F₂₁, summation ΣF=1. Net exchange Q₁₂=A₁F₁₂σ(T₁⁴-T₂⁴) for black surfaces; radiation networks add surface resistances (1-ε)/(Aε).
Parallel plates close together have F₁₂≈1.
View factors determine how much radiation leaves one surface and reaches another, which is needed for radiant enclosures and furnace design.
Fraction of radiation leaving one surface that strikes another.
View factors determine how much radiation leaves one surface and reaches another, which is needed for radiant enclosures and furnace design.
The fraction of radiation leaving one surface that directly reaches another surface, and it depends only on geometry.
A circuit analogy where surface resistances and space resistances are combined to find heat flows between surfaces.
Typical applications include finding the net radiation between two parallel plates in a furnace, calculating heat loss from a small object inside a large enclosure and designing a radiant heater layout to heat a floor evenly.
Study "Radiation" first (topic 89 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
Charts for standard geometries. Shielding with parallel plates. Enclosure rule.
Parallel plates close together have F₁₂≈1.
The next topic is "Fins", which builds directly on this one.
It is classed as Advanced in Thermodynamics & Fluids (topic 90 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.