Thermosiphon
This article includes a list of general references, but it lacks sufficient corresponding inline citations. (March 2009) |
Thermosiphon (or thermosyphon) is a method of passive heat exchange, based on natural convection, which circulates a fluid without the necessity of a mechanical pump. Thermosiphoning is used for circulation of liquids and volatile gases in heating and cooling applications such as heat pumps, water heaters, boilers and furnaces. Thermosiphoning also occurs across air temperature gradients such as those utilized in a wood fire chimney or solar chimney.
This circulation can either be open-loop, as when the substance 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 container. Its purpose is to simplify the transfer of liquid or gas while avoiding the cost and complexity of a conventional pump.
Simple thermosiphon
Heat pipes
In some situations the flow of liquid may be reduced further, or stopped, perhaps because the loop is not entirely full of liquid. In this case, the system no longer convects, so it is not a usual "thermosiphon".
Heat can still be transferred in this system by the evaporation and condensation of vapor; however, the system is properly classified as a heat pipe thermosyphon.[1][2] If the system also contains other fluids, such as air, then the heat flux density will be less than in a real heat pipe, which contains only a single substance.
The thermosiphon has been sometimes incorrectly described as a 'gravity return heat pipe'.[3] Heat pipes usually have a wick to return the condensate to the evaporator via capillary action. A wick is not needed in a thermosiphon because gravity moves the liquid.[4] The wick allows heat pipes to transfer heat when there is no gravity, which is useful in space. A thermosiphon is "simpler" than a heat pipe.[5]
(Single-phase) thermosiphons can only transfer heat "upward", or away from the acceleration vector. Thus, orientation is much more important for thermosiphons than for heatpipes. Also, thermosiphons can fail because of a bubble in the loop, and require a circulating loop of pipes.
Reboilers and calandria
If the piping of a thermosiphon resists flow, or excessive heat is applied, the liquid may boil. Since the gas is more buoyant than the liquid, the convective pressure is greater. This is a well known invention called a reboiler. A group of reboilers attached to a pair of plena is called a calandria. In some circumstances, for example the cooling system for an older (pre 1950s) car, the boiling of the fluid will cause the system to stop working, as the volume of steam created displaces too much of the water and circulation stops.
The term "phase change thermosiphon" is a misnomer and should be avoided.[citation needed] When phase change occurs in a thermosiphon, it means that the system either does not have enough fluid, or it is too small to transfer all of the heat by convection alone. To improve the performance, either more fluid is needed (possibly in a larger thermosiphon), or all other fluids (including air) should be pumped out of the loop.
Solar energy
Thermosiphons are used in some liquid-based
Architecture
In locations historically dominated by permafrost conditions, thermosiphons may be used to counter adverse geologic forces on the foundations of buildings, pipelines and other structures caused by the thawing of the permafrost.[7] A study published in 2006 by oil giant ConocoPhillips reports that Alaska's permafrost, upon which much of the state's infrastructure is built, has degraded since 1982 amid record warm temperatures.[8] According to the Alaska Climate Research Center at the University of Alaska Fairbanks, between 1949 and 2018 the average annual temperature in Alaska rose 4.0 degrees Fahrenheit, with an increase of 7.2 degrees Fahrenheit over the winter.[9]
Computing
Thermosiphons are used for
Uses
Without proper cooling, a modern processor chip can rapidly reach temperatures that cause it to malfunction. Even with a common heat sink and fan attached, typical processor operating temperatures may still reach up to 70 °C (160 °F). A thermosiphon can efficiently transfer heat over a much wider temperature range and can typically maintain the processor temperature 10–20 °C cooler than a traditional heat sink and fan. In some cases, it is also possible that a thermosiphon may cover multiple heat sources and, design-wise, be more compact than an appropriately sized conventional heat sink and fan.
Drawbacks
Thermosiphons must be mounted such that vapor rises up and liquid flows down to the boiler, with no bends in the tubing for liquid to pool. Also, the thermosiphon's fan that cools the gas needs cool air to operate. The system has to be completely airtight; if not, the process of thermosiphon will not take effect and cause the water to only evaporate over a small period of time.
Engine cooling
Some early cars, motor vehicles, and engine-powered farm and industrial equipment used thermosiphon circulation to move cooling water between their
Espresso Machines
Many espresso machine designs use a thermosiphon in order to maintain a stable temperature.
The E-61 espresso machine has a group head with a thermosiphon. This group head is common on many espresso machines today.
Some lever espresso machines have a double wall around the piston in their group that is used for a thermosiphon. A modern example would be the machines from Londinium.
See also
- Convection – Fluid flow that occurs due to heterogeneous fluid properties and body forces
- Geothermal heat pump– System to transfer heat to/from the ground
- Heat pipe – Heat-transfer device that employs phase transition and Loop heat pipe – two-phase heat transfer device
- Passive solar– Architectural engineering that uses the Sun's heat without electric or mechanical systems
- Reboiler – Heat exchangers typically used to provide heat to the bottom of industrial distillation columns
- Siphon – Device involving the flow of liquids through tubes
- Solar heating– Device that collects heat
- Thermic siphon – Heat-exchanging element in the firebox of some steam boilers
- Vapor-compression refrigeration – Refrigeration process
- Watercooling– Method of heat removal from components and industrial equipment
- Thomas Fowler (inventor) – British inventor
References
- ^ "Thermosyphon technology for Artificial Ground Freezing (AGF)". simmakers.com. Simmakers Ltd. 2017. Archived from the original on 5 Mar 2021. Retrieved 23 Jan 2021.
- ^ Holubec I (2008). "Flat Loop Thermosyphon Foundations in Warm Permafrost (Prepared for Government of the NT Asset Management Division Public Works and Services and Climate Change Vulnerability Assessment Canadian Council of Professional Engineers" (PDF). geocryology.files.wordpress.com.
- ^ "Evacuated Tube Heat Pipe Principles". BTF Solar. 2007. Archived from the original on 17 Aug 2014. Retrieved 23 Jul 2021.
- ^ "Thermosiphon Heat Exchangers". Apogee Interactive. Archived from the original on 3 Apr 2013. Retrieved 23 Jul 2021.
- ^ Haslego, C (Nov 8, 2010). "What is a Heat Pipe?". Cheresources.com Community. Archived from the original on Oct 27, 2023.
- S2CID 138026949.
- ^ Wagner AM (2014). "Review of Thermosyphon Applications" (PDF). ERDC/CRREL TR-14-1. US Army Engineer Research and Development Center (ERDC). Archived (PDF) from the original on June 25, 2021. Retrieved 24 Jun 2021.
- .
- ^ "Total Change in Mean Seasonal and Annual Temperature (°F), 1949-2018". Alaska Climate Research Center (Chart from article). Geophysical Institute, University of Alaska Fairbanks. Archived from the original on 2021-09-09. Retrieved 2021-06-25.
{{cite web}}
: External link in
(help)|type=
- ^ Kuemel B (2005). "CPU Vapor Cooling Thermosyphon". overclockers.com. Retrieved 26 Aug 2012.