A condenser, for cooling a gas flow containing a vapor to promote condensation of the vapor, has a generally cylindrical chamber. Gas is admitted at one end of the chamber and is given a swirl component of velocity. The gas then travels axially along the length of the chamber, and passes radially through poles into the bore of a separator. The swirl velocity of the gas flow tends to through water droplets radially outwards, where they can drain down the inside of a casing defining the chamber. The separator can include a skirt portion separating the main chamber from a water collection compartment. Cooling to cause condensation is provided by an external jacket, preferably having a coolant flowing through it in a helical fashion.
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