The survival still is a classic example of a flat sheet condenser. The plastic sheet has plenty of area, but makes a poor condenser because it is not well cooled and also has high thermal resistance. Placing one end in the shade improves the performance, and providing more cooling through evaporation makes it work even better. Placing a sheet of metal on top of the plastic above the collection cup boosts the efficiency tremendously, because metal has much lower thermal resistance than plastic and "wicks" the heat. These small modifications can make the difference between too little water and enough to keep you alive!
The simple Liebig condenser is commonly used in laboratories and schools. It is just a straight tube that carries vapor through a cooling jacket of water. A length of plastic tubing surrounded by air is a Liebig condenser in principle, and you can't get simpler than that! Clearly, the longer the tube, the more cooling area, and the colder the water you pass through the jacket the better it is at condensing vapor. In principle, this condenser may be used "in reverse" by passing the coolant through the central tube and the vapor through the jacket, but its efficiency will be poor.
In use, the orientation of a condenser can have a large effect on its efficiency. As we all know, hot air rises and cool air sinks. Feeding hot vapor into the top of a condenser will be pushing it against its natural direction of movement, slowing it down and giving it more time to condense. If you feed hot vapor into the bottom of a condenser, it will tend to move rapidly to the top and require more cooling power. This is why diagrams of laboratory set-ups show the condenser sloping down at an angle, with the vapor entering at the top.
If you lengthen the central tube in a Liebig condenser and wind it into a spiral, you have created a Graham condenser. The moonshiner's "worm" in a barrel of water is a Graham condenser if you consider the barrel of water as a large water jacket. The Graham condenser must be used vertically. If it is set at an angle, liquid will settle in the bottom of each turn of the coil, and block the flow of vapor.
The Vigreux condenser looks complicated but is just a Liebig condenser with its surface area increased by pushing indentations into the sides of the tube. Many variations on this theme exist. It's easily made in glass, but would be a nightmare to duplicate in metal.
The metal equivalent of a Vigreux condenser is the hedgehog, where surface area of a metal tube is increased by fitting it with fins or spines on the inside, the outside or both. This significantly increases the efficiency of a condenser.
Firebox or Shotgun condenser
Line a bunch of vapor tubes up side by side, and enclose them in one cooling jacket. This is called a Firebox or Shotgun condenser. The "Firebox" name comes from the fact that this same design was used in steam locomotives to generate steam. It is sometimes called a "Shotgun" because it features several parallel tubes, or "barrels".
The Cold Finger
The Cold Finger
All the designs we've considered so far carry the vapor on one side of a sheet with coolant on the other side, or inside a tube surrounded by coolant. The Cold Finger condenser reverses that, and is a tube carrying coolant that is inserted into the vapor to be condensed. This is a simple and very useful condenser that can easily be dropped into the top of a column of vapor, and is also easily removed and cleaned.
You can increase the surface area of a Cold Finger by winding it into a coil, just like in the Graham condenser. This is the principle of a reflux coil. Like the Cold Finger, the reflux coil is usually inserted in the top of a column.
The Gloved Cold Finger combines both types of condensers into one, by placing a jacket or coil around the column of vapor and inserting a Cold Finger or Reflux Coil inside it. This is an extremely efficient design, because cooling is applied to the vapor from two directions.
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