film evaporators are used extensively in chemical process
industry, food and paper industry. Due to the absence
of static head effect caused by liquid column as in
other types of evaporators, evaporation can take place
at very small effective mean temperature differences.
The temperature difference are typically between 3 -
8oC. This is significantly less than in other devices
used for evaporation, e.g. forced reboilers or kettle
evaporators, here the effective mean temperature difference
is between 15
and 300C. The film heat transfer coefficients are in
general high, and characterised by surface boiling.