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Nucleation of the crystal is then being prevented by a substantial barrier. This has consequences, for example cold high altitude clouds may contain large numbers of small liquid water droplets that are far below 0 °C. In small volumes, such as in small droplets, only one nucleation event may be needed for crystallisation.
The critical heat flux is the peak on the curve between nucleate boiling and transition boiling. The heat transfer from surface to liquid is greater than that in film boiling. Nucleate boiling is common in electric kettles and is responsible for the noise that occurs before boiling occurs. It also occurs in water boilers where water is rapidly ...
In clouds warmer than about −37 °C where liquid water can persist in a supercooled state, ice nuclei can trigger droplets to freeze. [ 1 ] Contact nucleation can occur if an ice nucleus collides with a supercooled droplet, but the more important mechanism of freezing is when an ice nucleus becomes immersed in a supercooled water droplet and ...
For example, if water is nucleating in supersaturated air, then is the free energy per unit of volume of water minus that of supersaturated air at the same pressure. As nucleation only occurs when the air is supersaturated, is always negative. The second term comes from the interface at surface of the nucleus, which is why it is proportional to ...
This process only happens at temperatures between 0 °C (32 °F) and −40 °C (−40 °F). Below −40 °C (−40 °F), liquid water will spontaneously nucleate, and freeze. The surface tension of the water allows the droplet to stay liquid well below its normal freezing point. When this happens, it is now supercooled liquid water.
An example would be when someone takes a cup of superheated water from a microwave and, when jiggling it with a spoon or against the wall of the cup, heterogeneous nucleation occurs and most of water particles convert into steam. If the change in phase forms a crystalline solid in a liquid matrix, the atoms might then form a dendrite.
The freezing speed directly influences the nucleation process and ice crystal size. A supercooled liquid will stay in a liquid state below the normal freezing point when it has little opportunity for nucleation; that is if it is pure enough and has a smooth enough container. Once agitated it will rapidly become a solid.
Homogeneous nucleation, where the bubbles form from the surrounding liquid instead of on a surface, can occur if the liquid is warmer in its center, and cooler at the surfaces of the container. This can be done, for instance, in a microwave oven, which heats the water and not the container.