Thermal Transmittance - U

Thermal transmittance - U - from thermal resistance

Thermal transmittance from thermal resistance can be expressed as

U = 1 / R         (1)

where

U = overall thermal transmittance (W/m^{2 o}C)

R = thermal resistance (m^2oC/W)

Overall thermal transmittance from individual thermal resistances can be expressed as

U = 1 / Σ R_i         (2)

Example - thermal transmittance of an heat exchanger

The thermal transmittance of an heat exchanger can be calculated like

U = 1 / (R_{air film} + R_{condensate film} + R_{metal wall} + R_{product film})

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