Condenser

This is where vapour returns to being liquid. The pipe it flows through runs inside a jacket filled with cooling water.

The water is sent against the direction of the vapour — in at the distillate outlet, out at the vapour inlet. It looks backwards but it makes sense: the coldest water meets liquid that is already cool, and the warmed water meets the hottest vapour. The temperature difference is then similar at every point and the heat exchange most effective. Running it with the flow also works, but takes considerably more water.

The simplest design is the Liebig condenser — a pipe in a jacket, not very efficient but easy to make. A worm lengthens the vapour path over the same overall length. Shell and tube, with a bundle of parallel pipes, gives the largest exchange area and is what serious setups use.

This is also where the glass-versus-metal argument shows most clearly. Metal conducts heat hundreds of times better, so it condenses more efficiently at the same size. Glass repays you with chemical indifference — nothing passes from it into the distillate. That choice is worked through in the equipment wizard.