Hey gang,

If I'm gently heating (~51°C) a solution to reduce its volume through evaporation, would it be faster to blow a fan across the top and risk lowering the solution's temperature trough thermal exchange with the solvent/side of the pan, or would the added airflow across the top help the solvent evaporate?

Basically, evaporating with artificial heat: aided or impeded through artificial airflow?

Definitely aided.

Your solution temp drops under a fan because the airflow removes the fastest/most energetic water molecules that
escaped the liquid. The water vapor pressure over the solution drops and evaporation rate rise. If your goal is to keep the liquid temp the same temp, airflow over the surface lets you increase your hotplate temp thus increasing evaporation rate even further.

Factors that increase evaporation rate:
1. Solution temp.
2. Airflow over the liquid surface.
3. Ambient pressure (lower pressure -> faster evaporation).
4. Surface area of the solution (greater area -> faster evaporation).
5. Agitation of the solution (it increases heat transfer rate within the solution and its surface area).

You can use any of the above to speed up the evaporation process. That's why rotovaps are so efficient.

It will definitely evaporate faster with heat + a fan, you are removing the highest energy molecules from just above the surface of the liquid, allowing more to fill that space and be removed etc.