Thermal Transmittance vs. Thermal Resistance
The thermal transmittance U vs. the thermal resistance R.
Thermal transmittance related to thermal resistance can be expressed as
U = 1 / R (1)
where
U = overall thermal transmittance (W/m2 oC)
R = overall thermal resistance (m2oC/W)
Thermal resistance can be expressed by transforming (1) to
R = 1 / U (1b)
The overall thermal transmittance from a layered construction with individual thermal resistances - like a wall with insulation and outside and inside cladding - can be expressed as
U = 1 / ΣRi (2)
Example - Thermal Transmittance in Heat Exchanger
The thermal transmittance in an heat exchanger can be calculated as
U = 1 / (Rair film + Rcondensate film + Rmetal wall + Rproduct film)
