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Some observations of the frost formation in free convection: with and without the presence of electric field.

Author(s) : WANG C. C., HUANG R. T, SHEU W. J., et al.

Type of article: Article

Summary

An experimental study concerning the frost formation in natural convection subjected to the influence of EHD was conducted. For the ambient temperature above the sub-freezing point and without the influence of EHD, water vapour deposited on the surface in the form of small droplets. A significant amount of coalescence of the small droplets was seen at the early stage of frost formation and the number of droplets increased with the relative humidity, but the size of the droplets decreased with the rise of the relative humidity. A hexagonal structure was observed as the droplet grew over a critical size. However, when the ambient temperature was below the sub-freezing temperature, the hexagonal structure was not seen because of the lack of droplets coalescence and the frost structure is comparatively uneven. With the presence of EHD, the ice column was pulled up towards the electrode and the structure was relatively skinny and fragile. The fragile structure can easily break up and fall off due to the influence of gravity. It was also found that the electric polarity plays a significant role on the frost growth. For a negative polarity, the frost structure was thinner than for a positive polarity and the break-off frequency of the ice column was more frequent compared with a positive polarity. It is likely that this phenomenon is related to the opposite direction of the dielectrophoreic force and the electrostrictive force at a positive polarity whereas the direction of the dielectrophoreic force and the electrostrictive force are the same at a negative polarity.

Details

  • Original title: Some observations of the frost formation in free convection: with and without the presence of electric field.
  • Record ID : 2005-0091
  • Languages: English
  • Source: International Journal of Heat and Mass Transfer - vol. 47 - n. 14-16
  • Publication date: 2004/07

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