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Information about Thermosiphon

Thermosiphon (alt. thermosyphon) refers to a method of passive heat exchange based on natural convection which circulates liquid in a vertical closed-loop circuit without requiring a conventional pump. 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.

Simple thermosiphon

Convective movement of the liquid starts when liquid in the loop is heated, causing it to expand and become less dense, and thus more buoyant than the cooler water in the bottom of the loop. Convection moves heated liquid upwards in the system as it is simultaneously replaced by cooler liquid returning by gravity. In many cases the liquid flows easily because the thermosiphon is designed to have very little hydraulic resistance.

Phase change thermosiphon

In other cases when the loop has more resistance to flow, the liquid may be heated beyond its boiling point, causing a phase change as the liquid evaporates to a gas (such as steam). Since the gas is much more buoyant than the hot liquid, the convective pressure is increased considerably. This is known as a heat pipe thermosiphon. It allows the cooling and heating of objects by changing the phase of a liquid inside a closed system, and operates on the principles of buoyancy to move the fluid through the system.

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, then the system no longer operates on convection principles, so it is no longer a simple "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.

A thermosiphon reboiler is called a calandria.

The thermosiphon has been sometimes incorrectly described as a 'gravity return heat pipe' [1]. A wick is usually a necessary feature of a heat pipe to allow the return of condensate to the evaporator via capillary action, whereas this function is not needed in a thermosiphon as gravity allows the movement of the liquids [2]. The wick allows heat pipes to conduct heat exchange against gravity (so leading to heat pipe use in space applications); against this a thermosiphon can be seen as a 'simpler' heat pipe [3]. It follows that correct orientation is much more important for thermosiphons than for heatpipes.

Solar energy

Thermosiphons are used in some liquid-based solar heating systems to heat a liquid such as water. The water is heated passively by solar energy and relies on heat energy being transferred from the sun to a solar collector. The heat from the collector can be transferred to water in two ways: directly where water circulates through the collector, or indirectly where an anti-freeze solution carries the heat from the collector and transfers it to water in the tank via a heat exchanger. Convection allows for the movement of the heated liquid out of the solar collector to be replaced by colder liquid which is in turn heated. Due to this principle, it is necessary for the water to be stored in a tank above the collector.

Computing

Thermosiphons are used in computing to describe a system for watercooling the internal computer components, most commonly referring to the processor. While any suitable liquid can be used, water is the easiest liquid to use in thermosiphon systems. Unlike traditional watercooling systems, thermosiphon systems do not rely on a water pump (or a pump for other liquids) but rely on convection for the movement of heated water (which may become vapour) from the components upwards to a heat exchanger. There the water is cooled and is ready to be recirculated. The most commonly used heat exchanger is a radiator where air is blown actively through a fan system to condense the vapour to a liquid. The liquid is recirculated through the system, thus repeating the process. No pump is required - the vaporization and condensation cycle is self sustaining.

Uses

Modern processors get relatively hot. Even with a common heat sink and fan cooling the processor, operating temperatures may still reach up to 70°C (158°F). A thermosiphon can handle heat output at a much wider temperature range than any heat sink and fan, and can maintain the processor 10-20°C cooler. In some cases a thermosiphon may also be less bulky than a normal 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 thermosiphons' fan that cools the gas needs cool air to operate.

Ground cooling

Heat pipes are used at locations in higher latitudes like northern Alaska and Canada to prevent ice-rich permafrost from melting below buildings and other infrastructure such as schools, air hangars, community water tanks, and even some stretches of highway. Heat pipes are also a common feature along the length of the Trans-Alaska Pipeline System. In these applications the solution in the pipes is often carbon dioxide or ammonia. At the bottom of the heat pipe, heat from the ground warms the liquid and converts it to a vapor. Cooling from the heat sink fins above ground releases this heat to the atmosphere and causes the vapor to condense on the outer pipe wall, which then drains back into the liquid pool at the bottom of the heat pump.

See also

References

Heat exchange may refer to:
  • Heat transfer, an area of engineering concerned with the transfer of thermal energy (heat)
  • A heat exchanger, a device used to exchange energy between fluids
Devices designed to perform a heat exchange include:

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Convection in the most general terms refers to the movement of currents within fluids (i.e. liquids, gases and rheids).

Convection is one of the major modes of heat and mass transfer.
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In physics, buoyancy is the upward force on an object produced by the surrounding fluid (i.e., a liquid or a gas) in which it is fully, or partially immersed, due to the pressure difference of the fluid between the top and bottom of the object.
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Hydraulics is a topic of science and engineering dealing with the mechanical properties of liquids. Hydraulics is part of the more general discipline of fluid power. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid
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phase transition or phase change is the transformation of a thermodynamic system from one phase to another. The distinguishing characteristic of a phase transition is an abrupt change in one or more physical properties, in particular the heat capacity, with a small change in
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Gas is one of the four major states of matter, consisting of freely moving atoms or molecules without a definite shape. Compared to the solid and liquid states of matter a gas has lower density and a lower viscosity.
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In physical chemistry, and in engineering, steam refers to vaporized water. It is a pure, completely invisible gas (for mist see below). At standard atmospheric pressure, pure steam (unmixed with air, but in equilibrium with liquid water) occupies about 1,600 times the
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A heat pipe is a heat transfer mechanism that can transport large quantities of heat with a very small difference in temperature between the hotter and colder interfaces.
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In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i.e. density, crystal structure, index of refraction, and so forth).
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A closed system is a system in the state of being isolated from the environment. It is often used to refer to a theoretical scenario where perfect closure is an assumption, however in practice no system can be completely closed; there are only varying degrees of closure.
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In physics, buoyancy is the upward force on an object produced by the surrounding fluid (i.e., a liquid or a gas) in which it is fully, or partially immersed, due to the pressure difference of the fluid between the top and bottom of the object.
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Evaporation is the process by which molecules in a liquid state (e.g. water) spontaneously become gaseous (e.g. water vapor), without being heated to boiling point. It is the opposite of condensation.
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Condensation is the change in matter of a substance to a denser phase, such as a gas (or vapor) to a liquid.[1] Condensation commonly occurs when a vapor is cooled to a liquid, but can also occur if a vapor is compressed (i.e.
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A heat pipe is a heat transfer mechanism that can transport large quantities of heat with a very small difference in temperature between the hotter and colder interfaces.
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Reboilers are heat exchangers typically used to provide heat to the bottom of industrial distillation columns. They boil the liquid from the bottom of a distillation column to generate vapors which are returned to the column to drive the distillation separation.
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A calandria is the reactor core of the CANDU reactor. The calandria contains heavy water, a moderator used to moderate neutrons to achieve nuclear fission.

A calandria is also a shell-and-tube unit used as a thermosiphon reboiler for distillation or evaporation.
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A heat pipe is a heat transfer mechanism that can transport large quantities of heat with a very small difference in temperature between the hotter and colder interfaces.
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Condensation is the change in matter of a substance to a denser phase, such as a gas (or vapor) to a liquid.[1] Condensation commonly occurs when a vapor is cooled to a liquid, but can also occur if a vapor is compressed (i.e.
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evaporator changes liquids into gaseous state. For instance, water is heated and changed into steam. Therefore, it is the opposite of a condenser.

Within a downstream processing system, several stages are used to further isolate and purify the desired product.
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Capillary action, capillarity, capillary motion, or wicking is the ability of a substance to draw another substance into it. The standard reference is to a tube in plants but can be seen readily with porous paper.
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Solar heating is the usage of solar energy to provide process, space or water heating. The heating of water is covered in solar hot water. Solar heating design is divided into two groups:

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Water is a common chemical substance that is essential to all known forms of life.[1] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor.
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Passive is the opposite of active. It has several specific meanings:
  • Passive voice of a verb
  • Passive components in electronics
  • Passive mode in File Transfer Protocol
  • Passive house, a standard for energy efficient buildings

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Solar energy is energy from the sun. It supports life on Earth and drives the Earth's weather. Solar energy predominantly arrives in the form of infrared, visible and ultraviolet light, and is either returned back to space or is absorbed.
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In thermal physics, thermal energy is the energy portion of a system that increases with its temperature. In a loose sense, "thermal energy" is a term often used to describe the energy content of a system related to heating effects, e.g. temperature increase or decrease.
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A solar collector is a device for extracting the energy of the sun directly into a more usable or storable form.
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Antifreeze is used in internal combustion engines, and for many other heat transfer applications, such as electronics cooling and chillers for HVAC. Compounds are added to water to reduce the freezing point of the mixture to below the lowest temperature that the system is likely to
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A heat exchanger is a device built for efficient heat transfer from one fluid or gas to another, whether the fluids are separated by a solid wall so that they never mix, or the fluids are directly contacted.
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should be added to this article, to conform with Wikipedia's Manual of Style.
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A solar collector is a device for extracting the energy of the sun directly into a more usable or storable form.
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Water cooling is a method of heat removal from components. As opposed to air cooling, water is used as the heat transmitter. Water cooling is commonly used for cooling internal combustion engines in automobiles and electrical generators.
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