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Combined convection and radiation

A hot surface in air usually loses heat through both convection and radiation at once, and the two contributions must be added to find the total heat loss. At low temperature differences convection often dominates, while radiation becomes increasingly important at higher temperatures because of its $T^4$ dependence.

\dot Q_{tot} = hA(T_s-T_\infty) + \varepsilon\sigma A(T_s^4-T_{surr}^4)

combined heat loss from the same surface

Symbols

$h$	heat transfer coefficient	W/(m²·K)
$\varepsilon$	emissivity

Example

A pipe surface with $A = 1.0$ m² gives $\dot Q_{conv} = 300$ W by convection and $\dot Q_{rad} = 150$ W by radiation. Total heat loss: $\dot Q_{tot} = 300+150 = 450$ W.

Do not assume convection and radiation are mutually exclusive – from a hot surface in air, both usually happen at once.

Practise radiation and transient heat for free →

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Part of Heat Transfer: Radiation and transient heat.