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Newton's law of cooling

Convection is heat transfer between a surface and a fluid flowing past it. Newton's law of cooling says the heat flow is proportional to the temperature difference between the surface and the fluid far away, through the heat transfer coefficient $h$ , which depends on geometry, fluid and flow conditions.

\dot Q = hA(T_s - T_\infty)

Symbols

$h$	heat transfer coefficient	W/(m²·K)
$T_s$	surface temperature	K
$T_\infty$	fluid temperature far away	K

Example

A plate with $A = 0.3$ m² and $h = 40$ W/(m²·K) has a $45$ K temperature difference from the air. $\dot Q = 40\cdot 0.3\cdot 45 = 540$ W.

h

is not a material property like

k

– it depends on the flow and often has to be found from correlations or given in the problem.

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Part of Heat Transfer: Convection.