Passive Two-Phase Solution
A schematic representation of a loop thermosyphon

Working principle

We let gravity do the work !

In a closed loop, working fluid is partially evaporated at a lower elevation (in the evaporator). By buoyancy, the two-phase mixture reaches the condenser at a higher elevation through the riser. It is cooled down and changes into liquid again, before finally draining into the evaporator through the downcomer. Because the two-phase mixture’s density in the riser is lower than that of the liquid in the downcomer, gravity sustains the flow, removing the need for mechanical drivers.

An icon of a ruler showing the difference of height needed for a thermosyphon system.

Loop Thermosyphons (LTS) gravity-driven cooling requires elevation between evaporator and condenser

Animation showing the working principle of Loop-Thermosyphon cooling systems.

Passive two-phase cooling refers to the cooling of components using a working fluid that undergoes phase change and has self-sustained motion driven by the application/extraction of heat.

No moving part icon.


Loop Thermosyphons consist of three main components, as describe below.
Here heat enters the system, where it is transferred from the heat source into the working fluid, resulting in partial evaporation. Multi-micro channel evaporators are typically used.
A schematic representation of an evaporator with microchannels
Here fluid flow circulates between evaporator and condenser. The riser and downcomer can either be adiabatic or participate to heat transfer. They also includes bends and turns.
Icon of a bended tube
Here heat exits the system. It is removed by the coolant, resulting in total condensation and subcooling of the working fluid. The condenser can be cooled by natural or forced convection with air, gas or liquid.
A schematic representation of a liquid-cooled condenser
A schematic representation of an air-cooled condenser


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