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Electrostatic suppression of the Leidenfrost Effect

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Evaporating liquid droplet floating above the hot surface, its weight supported by the slightly higher pressure in the thin layer of its vapor between the droplet and the surface, is known as the Leidenfrost effect and this has serious ramifications for process phenomena such as steam generation, thermal desalination, and quenching of metals. Boiling heat transfer is severely degraded at high surface temperatures due to the formation of this vapor layer, which causes dryout and temperature excursions.

 

In this project, we investigated the fundamental mechanism and identify the competing forces underlying the limits of electrostatic suppression of the Leidenfrost state. We observed and analyzed the electrohydrodynamic instabilities occurring above the threshold voltage that result in a wavy liquid-vapor pattern with a characteristic wavelength. In this work, the distinguishing feature is the presence of evaporation that adds an additional stabilizing force and leads to a critical electric field for suppression. Through a combination of linear stability analysis and experimentation, we determined the influence of material properties and surface temperature on the threshold electrical potential necessary to suppress the Leidenfrost effect. We also predicted and analyzed the wavelength and time constant of the fastest growing mode of disturbance at the interface. The developed modeling framework shows a good match with experimental data and identifies the electroviscous number as the key determinant of Leidenfrost state suppression

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References

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