A tube within a tube.
Many generator coolers sit very close to the alternator or generator windings. Very high value plant where any ingress of water would be catastrophic.
For this reason, clients sometimes specify “double wall tube”.
In simple terms; the double tube unit consists of two tubes that are joined by expansion. The outer tube is equipped with the necessary drainage system. If a leakage occurs the fluid runs through this drainage system and sets off an alarm.
External fins are attached, so that the appearance of the cooler is precisely the same as any other air cooler. The difference is, there can be no water leakage!