Nucleate boiling
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Nucleate boiling means some type of boiling that can take place under certain conditions; the process of forming steam bubbles within liquid in micro cavities adjacent to the wall if the wall temperature at the heat transfer surface rises above the saturation temperature while the bulk of the liquid (heat exchanger) is subcooled. The bubbles grow until they reach some critical size, at which point they separate from the wall and are carried into the main fluid stream. There the bubbles collapse because the temperature of bulk fluid is not as high as at the heat transfer surface, where the bubbles were created [1].
Heat and mass transfer during nucleate boiling has a significant effect on the heat transfer rate. This heat transfer process helps quickly and efficiently to carry away the energy created at the heat transfer surface and is therefore sometimes desirable — for example in nuclear power plants, where liquid is used as a coolant. [2].
The effects of nucleate boiling take place at two locations:
- the liquid-wall interface
- the bubble-liquid interface [3]
The nucleate boiling process has a complex nature. A limited number of experimental studies provided valuable insights into the boiling phenomena, however these studies provided often contra dictionary data due to internal recalculation (state of chaos in the fluid not applying to classical thermodynamic methods of calculation, therefore giving wrong return values) and have not provided conclusive findings yet to develop models and correlations. Nucleate boiling phenomenon still requires more understanding [4].
