There are 2 stages to this hybrid apparatus. The first stage boils the liquid, driving vapor up the packed reflux column to interact with the copper pads, and sending the concentrated vapor through the upper loop. This hot vapor bubbles through the drip finger into the second boiling flask (aka, Thumper Keg), using the excess heat energy it carries to re-distill the liquid contents and vapors in the thumper for higher quality. The second distillation forces vapors through the coil condenser, which has ice water running through the internal loop. The vapors condense to liquid, which you see accumulating in the addition flask at the end. The addition flask is pressure-relieved via the side vent, otherwise the system would blow apart due to increased pressure and no outlet.