High Quality Content by WIKIPEDIA articles! Thermosiphon (alt. thermosyphon) refers to a method of passive heat exchange based on natural convection which circulates liquid without the necessity of a mechanical pump. This circulation can either be open-loop, as when liquid in a holding tank is passed in one direction via a heated transfer tube mounted at the bottom of the tank to a distribution point - even one mounted above the originating tank - or it can be a vertical closed-loop circuit with return to the original vessel. Its intended purpose is to simplify the pumping of liquid and/or heat transfer, by avoiding the cost and complexity of a conventional liquid pump.