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Flash evaporation is a process where a liquid instantly boils when heated and sent through a chamber with reduced pressure. This cooling effect can be used for refrigeration, desalination, and biofuel production. Boiling temperatures change with pressure, and flash evaporation uses this phenomenon to turn liquid into vapor. It can also be used to remove excess liquid from biofuels.
Flash evaporation is a process by which part of a liquid instantly boils – or flashes – after it has been heated and sent through a chamber under reduced pressure. It is the reduction in pressure that causes some of the liquid to vaporize. Vaporizing a liquid in this way absorbs heat and can cause the surrounding area to cool dramatically. This cooling effect allows the process to be used in some forms of refrigeration. Flash evaporation can also be used to purify liquids and, as such, can be used to desalinate water and aid in the creation of biofuels.
It is important to note that flash evaporation depends on the properties with which liquids evaporate. One of the most important of these properties is that the boiling point of a liquid can be increased or decreased depending on the atmospheric pressure exerted on it. For example, water boils at 212° Fahrenheit (100° Celsius) at sea level. That temperature drops to 194° Fahrenheit (90° Celsius) when you’re atop a 10,000-foot (about 3.05 kilometers) mountain because there’s less pressure there. Similarly, if atmospheric pressure is raised to two atmospheres (about 14.7 psi or 760 torr), water boils at 248° Fahrenheit (120° Celsius).
Boiling temperatures change with pressure because to boil a liquid must absorb enough heat for it to overcome atmospheric pressure and turn into vapor. At lower pressure, the boiling point of most liquids decreases because there is less pressure for the liquid to overcome to become a vapor. Flash evaporation uses this phenomenon. A liquid is heated and sent through a valve into a chamber with a lower pressure. The reduction in pressure causes some of the liquid to turn to vapor while the rest of the liquid cools.
The flashing process can absorb so much heat that some liquids can be flashed for use as cooling. This process is called self-refrigeration and is used in some vapor-compression refrigeration systems. Flash evaporation can also be used to desalinate water in a process called multi-stage flash distillation. In this process, the salt water is expelled and the steam is cooled into pure water. The remaining salt water can then be sent through a series of increasingly lower pressure chambers to be washed over and over again to produce more fresh water.
Flash evaporation can also be used in the production of biofuels. At different stages of biofuel production, one producer may need to remove one liquid from another. In that case, flash evaporation can be used to remove the more volatile liquid, i.e. a liquid that evaporates more easily, from the rest of the liquid. For example, the process is used to remove excess methone from fuel during the manufacturing process. Similarly, after the fuel has been further processed and purified, unwanted water can be removed using flash evaporation.
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