Heat Transfer — Cheat Sheet
Conduction, convection, radiation, thermal resistance networks, fins and dimensionless groups.
Conduction (Fourier)
| Plane wall | Q̇ = k·A·ΔT / L |
| Resistance | R = L / (k·A) |
| Cylindrical wall | R = ln(r₂/r₁) / (2πkL) |
| Series network | Q̇ = ΔT / ΣR |
Convection
| Newton cooling | Q̇ = h·A·ΔT |
| Resistance | R = 1 / (h·A) |
| Nusselt number | Nu = h·L / k |
| Overall | 1/UA = ΣR (conv + cond + conv) |
Radiation
| Net exchange | Q̇ = ε·σ·A·(T₁⁴ − T₂⁴) |
| Stefan-Boltzmann | σ = 5.67×10⁻⁸ W/m²K⁴ |
| Use absolute T | kelvin, not °C |
Fins & transient
| Fin heat rate | Q̇ = η_f·h·A_fin·ΔT |
| Biot number | Bi = h·L_c / k |
| Lumped valid | Bi < 0.1 |
| Fourier number | Fo = α·t / L_c² |
| Diffusivity | α = k / (ρ·c_p) |
Formula reference — verify against the governing standard. Not a substitute for engineering judgment.