The Reflux Coil

Many people prefer to make this type of coil condenser to condense vapor at the top of a column because it is simple to make, despite its complicated appearance. Since it is most often used to condense reflux, it is simply called a Reflux Coil.

Soft copper tubing 5mm (3/16 inch) to 6.5mm (% inch) in diameter is the best material to use. This size tubing is widely sold in coils for use in hydraulic lines, refrigeration and some plumbing applications. The smaller diameter tubing is better, because it is easier to bend and less likely to flatten, but the larger size can be used if you're careful.

You need a hollow former to make a reflux condenser. This could be a short length of pipe with an outside diameter matching the inside diameter of the coil you want to wind. Even with 5 mm (3/16 inch) tubing, don't attempt to wind a coil smaller than 36mm (1/ inches) inside diameter, because the tubing will start to flatten out. You can calculate how much copper tubing you need, but as an example, 4% meters (14 feet) of 5mm (3/16 inch) tubing on a 36 mm (1 / inch) former will make 27 turns, leaving 150 mm (6 inches) free at each end for the connections at the top. The length of the coiled part is just over 250 mm (10 inches), and it will fit neatly into a 50 mm (2 inch) diameter column.

Start by threading the tubing through the middle of the former, leaving about 150 mm (6 inches) sticking out. This will be where the water hose is attached. Then, carefully form a looping bend and start winding the rest of the tubing around the former, back toward the end left sticking out. If you manage to keep all the coils close together, you should end up with about the same amount left over.

After removing the former, carefully stretch the coil out a little bit. You'll find that the coils will then be spaced apart by up to the diameter of the coil tubing. Finally, bend the two feed pipes at right angles to the coil (being careful not to kink the tubing) and you'll have a convenient "hanger" to hold the coil in place when you insert it into the top of the column. With a close fitting shroud, this condenser can easily handle up to 2 kW. The closeness of the shroud encourages vapor to flow between the coils rather than past them. Loosely packing metal scrubber material around the top of the reflux coil will encourage intimate contact between the vapor and the condenser coils (this trick also works with a Cold finger).

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