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# Thermal Transmittance vs. Thermal Resistance

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 / Σ Ri                                (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)

## Related Topics

### • Thermodynamics

Work, heat and energy systems.

## Related Documents

### Carnot Efficiency

The efficiency of the Carnot cycle.

### Conductive Heat Transfer

Conductive heat transfer takes place in a solid if there is a temperature gradient.

### Overall Heat Transfer Coefficients

Walls or heat exchangers - calculate overall heat transfer coefficients.

### Solids, Liquids and Gases - Thermal Conductivities

Thermal conductivity coefficients for insulation materials, aluminum, asphalt, brass, copper, steel, gases and more.

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