All courses › Heat Transfer › Convection in a composite wall

Convection in a composite wall

Convection at the surface of a wall gives a thermal resistance just like a conduction layer, and is placed in series with the wall's own layers. A realistic wall therefore has convection on both sides in addition to conduction through the materials between them.

R_{conv} = \dfrac{1}{hA}

thermal resistance for convection

R_{tot} = \dfrac{1}{h_iA} + \sum\dfrac{L_j}{k_jA} + \dfrac{1}{h_oA}

total resistance with convection on both sides

Symbols

$h_i,\ h_o$	indoor/outdoor heat transfer coefficient	W/(m²·K)
$R_{conv}$	convection resistance	K/W

Example

A wall has $h_i = 8$ , $h_o = 25$ W/(m²·K) and insulation $L = 100$ mm, $k = 0.03$ W/(m·K). Per area: $1/8 + 0.1/0.03 + 1/25 \approx 3.50$ m²K/W.

Do not forget the convection resistance

1/(hA)

on both sides – it is often just as important as the insulation layer itself.

Practise convection for free →

← Newton's law of cooling · The Biot number →

Part of Heat Transfer: Convection.