Watercooling
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Watercooling is a method of heat removal from components. Contrary to air cooling, it uses water as the heat transmitter and is commonly used for cooling internal combustion engines in automobiles and electrical generators. Other uses include cooling the lubricant oil of pumps; for cooling purposes in heat exchangers; and cooling products from tanks or columns.
The advantages of using water cooling over air cooling include water's higher specific heat capacity, density and thermal conductivity, meaning water can transmit heat over greater distances with much less volumetric flow and reduced temperature difference. This leads to the primary advantage watercooling enjoys over conventional heatsinks: the tremendously increased ability to transport heat away from source to a secondary cooling surface allows for large, more optimally designed radiators rather than small, inefficient fins mounted on or near a heat source such as a CPU core.
A disadvantage of water cooling is the risk of damage from freezing. Automotive and many other engine cooling applications require the use of a water and Antifreeze mixture to lower the freezing point to a temperature unlikely to be experienced. Anti-freeze also inhibits corrosion from dissimilar metals and can increase the boiling point, allowing a wider range of water cooling temperatures. It's distinctive odor also alerts operators to cooling system leaks and problems that would go unnoticed in a water-only cooling system.
Another less common chemical additive are products to reduce surface tension. These additives are meant to increase the efficiency of automotive cooling systems. Such products are used to enhance the cooling of underperforming or undersized cooling systems or in racing where the weight of a larger cooling system could be a disadvantage.
A typical watercooling setup consists of an object to be cooled, a pump which circulates the water and a radiator such as a large heatsink (possibly with a fan). These components are linked by tubes.
An optional watercooling component is a reservoir, which helps to prevent the formation of air bubbles in the system. However, if the watercooling system is properly configured and sealed, there is no need for a reservoir, though it does make the system much easier and less time-consuming to fill. Another option is simply using an inexpensive T-Line. There is no need for either of these components, though one is recommended to make the operation quicker to fill and bleed.
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[edit] Open method
An open watercooling system makes use of evaporative cooling, lowering the temperature of the remaining (unevaporated) water. A component such as a bong cooler replaces the radiator of a closed watercooling system. The obvious downside of this method is the need to continually replace the water lost due to evaporation.
[edit] Computer usage
In the past few years, watercooling has become important for cooling computer components, especially the CPU. Watercooling usually consists of a CPU water block, a water pump and a heat exchanger (usually a radiator with a fan attached). Watercooling not only allows for quieter operation and improved overclocking, but with improved heat handling capabilities hotter processors can be supported. Less commonly, GPUs, Northbridges, hard drives, memory,and even power supplies are also watercooled.
Watercoolers for computers (other than mainframes) were, up until the end of the 90's, homemade. They were put together using car radiators (or more commonly, heater cores), aquarium pumps and home made water blocks. More recently a growing number of companies are manufacturing premade, specialised components, allowing watercooling to be compact enough to fit inside a computer case. This, coupled with the growing amount of heat coming from the CPU has greatly increased the popularity of water cooling. However it is still a very niche market.
Dedicated overclockers will occasionally use vapor-compression refrigeration or thermoelectric coolers in place of more common standard heat exchangers. Watercooling systems in which water is cooled directly by the evaporator coil of a phase change system are able to chill the circulating coolant below the ambient air temperature (an impossible feat using a standard heat exchanger) and, as a result, generally provide superior cooling of the computer's heat-generating components. The downside of phase-change or thermoelectric cooling is that it uses much more electricity and antifreeze must be added due to the low temperature. Additionally, insulation, usually in the form of lagging around water pipes and neoprene pads around the components to be cooled, must be used in order to prevent damage caused by condensation of water vapour from the air on the surfaces at below ambient temperature. Common places from which to borrow the required phase change system are a household dehumidifier or air conditioner.
An alternative cooling system, which enables components to be cooled below the ambient temperature, but which obviates the requirement for antifreeze and lagged pipes, is to place a thermoelectric device (commonly referred to as a 'Peltier junction' or 'pelt' after Jean Peltier, who documented the effect) between the heat-generating component and the water block. Because the only sub-ambient temperature zone now is at the interface with the heat-generating component itself, insulation is required only in that localised area. The disadvantage to such a system is that pelts typically draw a large amount of power, and the watercooling system is required to remove this power, in addition to the heat generated by the component.
Apple's Power Mac G5 was the first mainstream desktop computer to have watercooling as standard.
[edit] Industrial usage
Most industrial cooling towers use river water or well water as their source of fresh cooling water. The large mechanical induced-draft or forced-draft cooling towers in industrial plants such as power plants, petroleum oil refineries, petrochemical plants and natural gas processing plants continuously circulate cooling water through heat exchangers and other equipment where the water absorbs heat. That heat is then rejected to the atmosphere by the partial evaporation of the water in cooling towers where upflowing air is contacted with the circulating downflow of water. The loss of evaporated water into the air exhausted to the atmosphere is replaced by "make-up" fresh river water or fresh cooling water. Since the evaporation of pure water is replaced by make-up water containing carbonates and other dissolved salts, a portion of the circulating water is also continuously discarded as "blowdown" water to prevent the excessive build-up of salts in the circulating water.[1]
Some industrial plants located in coastal areas use "once-through" seawater for their cooling needs and the warm seawater is returned and discharged offshore. Thermal pollution is an issue which needs to be addressed when waste cooling water is discharged into seas or rivers. On the other hand, the cooling water in such heat exchange cycles must be treated to prevent fouling in heat exchangers like condensers and other equipment.
High grade industrial water (produced by reverse osmosis) and potable water is sometimes used in industrial plants requiring high-purity cooling water.
Some nuclear reactors use heavy water as cooling. Most of the time, heavy water is employed in nuclear reactors because it is a moderator for the nuclear chain reaction. For the main cooling system, normal water is preferably employed through the use of a heat exchanger as heavy water is much more expensive. Reactors that use other materials for moderation (graphite) may also use normal water for cooling.
[edit] See also
- Computer cooling
- Cooling tower
- Cooling tower system
- Aircooling
- Heat pipe cooling
- Peltier cooling
- Thermosiphon
- Deep lake water cooling
- Heater Core
[edit] References
- ^ Beychok, Milton R. (1967). Aqueous Wastes from Petroleum and Petrochemical Plants, 1st Edition, John Wiley and Sons. LCCN 67-19834. (See Chapter 2 for material balance relationships in a cooling tower)
