Evaporation velocity of ethanol: adding ethanol vapour to a gas mixture I need to add a known amount of ethanol vapour to a gas mixture (He/Ar). To do that I let the mixture bubble in liquid ethanol kept at a known temperature (14 C).

The system is made of a large steel cylinder (d=20 cm; l=138cm) lying in horizontal position and half filled with liquid ethanol. the gas is bubbled trough the liquid on one side of the cylinder and extracted on the other side. 

The gas-flow trough the system is usually pretty low (~100ml/min) but I would like to increase it to ~10l/min and I need to know if this leaves enough time for the ethanol vapour to approach its equilibrium vapour pressure.
Please note that I have never done this. 

But are you sure that you want to rely on approximation/assumptions?

I realize that it needs additional changes to the experimental setup, but is measuring the ethanol concentration out of question? Gas sensors for ethanol are commercially available and a setup, in which they steer mass flow controllers is conceivable.

As a side note, you might be interested to see that ethanol sensors can be build in the lab: 

A Novel Flexible Room Temperature Ethanol Gas Sensor Based on SnO2 Doped Poly-Diallyldimethylammonium Chloride.