Theory 32/Lewis Number/Coating drying
Drying Is a Lewis Problem
The claim
The drying of a coating is set by its Lewis number, so two solvents with identical boiling points dry at different rates because their thermal and mass diffusivities differ.
01Mechanism
Evaporation cools the surface while vapour diffuses away; the ratio determines whether heat or mass transfer limits the rate.
02Prediction
Drying time should track Lewis.
03Refutation
Drying tracking boiling point would remove the ratio.