The evaporation rate of a rotary evaporator depends to a large extend on the immersion angle of the evaporating flask. The flatter the immersion angle, the higher the evaporation rate. This is, among other reasons, due to the fact that a flat immersion angle increases turbulence inside the evaporating flask, hence accelerating the evaporation. However, with a flatter immersion angle the evaporating flask cannot be as deeply immersed in the heating bath medium compared with a steep immersion angle. This can be an issue especially working with smaller evaporating flasks. Generally speaking, a 40 degrees immersion angle leads to a maximum efficiency rate without restriction in handling or risking losing parts of the sample due to over spilling and bumping into the receiving flask.
Achieve higher distillation efficiency when using a rotary evaporator – Impact of immersion angle