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Leidenfrost droplet Demonstration of the Leidenfrost effect Leidenfrost effect of a single drop of water. The Leidenfrost effect is a physical phenomenon in which a liquid, close to a solid surface of another body that is significantly hotter than the liquid's boiling point, produces an insulating vapor layer that keeps the liquid from boiling rapidly.
Superheating can occur when an undisturbed container of water is heated in a microwave oven. At the time the container is removed, the lack of nucleation sites prevents boiling, leaving the surface calm. However, once the water is disturbed, some of it violently flashes to steam, potentially spraying boiling water out of the container. [6]
The energy required to heat water is significantly lower than that needed to vaporize it, for example for steam distillation [10] and the energy is easier to recycle using heat exchangers. The energy requirements can be calculated from steam tables. For example, to heat water from 25 °C to steam at 250 °C at 1 atm requires 2869 kJ/kg.
Boiling occurs when the local temperature of the liquid reaches the saturation temperature, and further heat is supplied to allow the liquid to sufficiently phase change into a gas. Cavitation inception occurs when the local pressure falls sufficiently far below the saturated vapor pressure, a value given by the tensile strength of the liquid ...
The heat can be removed by channeling the liquid through a heat exchanger, such as a radiator, or the heat can be removed with the liquid during evaporation. [10] Water or glycol coolants are used to keep engines from overheating. [11] The coolants used in nuclear reactors include water or liquid metals, such as sodium or bismuth. [12]
Departure from nucleate boiling (DNB) occurs in sub-cooled flows and bubbly flow regimes. DNB happens when many bubbles near the heated surface coalesce and impede the ability of local liquid to reach the surface. The mass of vapor between the heated surface and local liquid may be referred to as a vapor blanket. Dryout
Rolling boil of water in an electric kettle. Boiling or ebullition is the rapid phase transition from liquid to gas or vapour; the reverse of boiling is condensation.Boiling occurs when a liquid is heated to its boiling point, so that the vapour pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere.
In liquid helium-4, the superfluidity occurs at far higher temperatures than it does in helium-3. Each atom of helium-4 is a boson particle, by virtue of its integer spin . A helium-3 atom is a fermion particle; it can form bosons only by pairing with another particle like itself, which occurs at much lower temperatures.