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6. Combined Convection & Conduction

The following equation can be used for estimating heat losses due to convection and conduction of an enclosure.

Q passive = (A x DT)/(x/k + 1/h)

Where:
Qpassive = heat load (W)
A = total external surface area of enclosure (m2)
x = thickness of insulation (m)
k = thermal conductivity of insulation (W/m °C)
h = convective heat transfer coefficient (W/m2 °C)
DT = Temperature change (°C)

Table II
Typical Values of Convection Heat Transfer Coefficient

Process h (W / m2 °C)
Free Convection – Air 2 – 25
Forced Convection – Air 25 – 250


Table III
Typical Values of Thermal Conductivity for Insulation

Product Thermal Conductivity (W / m°C)
Styrofoam .031
Polystyrene .037
Polyurethane .039