What is Thermosiphon?

Jeri Sullivan
Jeri Sullivan
Man with a drill
Man with a drill

Thermosiphon, also known as thermosyphon, is a process used to exchange heat from liquids without a pump. This eliminates cost and simplifies the heat transfer process. The most common ways thermosiphoning is accomplished is through water and solar convection.

The thermosiphon process can be used commercially in solar hot water heaters. A thermosiphon is a passive system, which means there are no mechanical moving parts. Instead, the system relies solely on the sun's energy to work. The water is collected in a piece of equipment called a batch collector, which is mounted on a building's roof. It is braced at an angle so when the water is collected, it can flow out using gravity.

Cold water is denser than warm water, so the storage tank is mounted slightly above the batch collector. As the sun heats the batch collector, the warm water rises and flows into the storage tank. Cold water sinks to the bottom and flows into a cold water supply line. This water is used for general cold faucet use.

The warm water moves into the storage tank, where it continues to be warmed by the sun. This continuous rise and fall of water based on the temperature creates convection and allows the thermosiphon to work. When hot water is needed, a faucet is turned on inside the building and the warm water from the storage tank flows through the hot water supply line.

Thermosiphon water systems can be used for ground cooling. Ground cooling is required in areas such as Alaska where structures are built on permafrost. Permafrost is soil that stays at or below freezing for long periods of time. The issue with building on permafrost is that it contains ice which can thaw if the temperature rises even for a short time. Intermittent thawing and refreezing of the permafrost can cause a building's foundation to weaken and crack.

Ground cooling can operate with underground pipes that are filled with carbon dioxide or ammonia. As the liquid is heated from the surrounding permafrost, it turns into vapor. As the vapor evaporates, it condenses on the outside of the pipes and converts back into a liquid. The cooled liquid flows into a collection tank and is reused.

Computer cooling is required because the processor that runs the computer can reach temperatures upwards of 160° Fahrenheit (71° Celsius). Though most computers are equipped with a fan, a thermosiphon is often able to reduce processor temperatures more effectively. In a computer thermosiphon, the fan acts as the convection vehicle by circulating the water so it will heat and convert to vapor. Similar to the ground cooling system, as the vapor cools it is recollected within the thermosiphon system and recycled.

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Discussion Comments


Ah, the good old water cooled computer CPU setup. Those are commonly used by overclockers. When one runs a CPU faster than its factory recommended settings, a lot of heat is generated and conventional fans can't get rid of it fast enough. Without those water cooling systems, that fast CPU could wind up as a burned out piece of junk.

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