Physical Properties in Evaporators

To calculate heat-transfer rates, physical-property data for the fluids being treated must be available. Physical property data should be as accurate as possible, especially as more accurate heat-transfer correlations become available. However, most physical properties of mixtures must be calculated or estimated; consequently there is little need to attempt to determine true film temperatures. Physical-property data at the average bulk fluid temperature are generally sufficient.

The following physical properties are usually required in order to obtain satisfactory calculated heat transfer rates:

1. viscosity
2. thermal conductivity
3. density
4. specific heat
5. latent heat
6. surface tension

When condensing or vaporizing over a temperature range, a curve representing heat load as a function of temperature should also be available. In addition, any concentration effects should be known.