Date of Publication:2015-01-01
Journal:科学通报
Affiliation of Author(s):化工学院
Volume:60
Issue:28/29
Page Number:2784-2789
ISSN No.:0023-074X
Abstract:Dropwise condensation caused by interfacial effects plays a crucial role
   in the thermal effciency and integration of power production. It is
   important to understand the effect of droplet dyanmic characteristics on
   heat transfer perfromace for the controlling mechanism of dropwise
   condensation heat transfer at low steam pressure and the development of
   efficient heat transfer techniques. Based on droplet departure
   characteristics in dropwise condensation at different steam pressures,
   the droplet departure retention effect at low pressure was proposed in
   this paper. Due to the increase of condensate viscosity at low steam
   pressure, the pulsation of droplet surface weakened and the contact
   angle hysteresis became apparent. Condensed droplets grew larger and
   moved more slowly in the departure process at low pressure compared to
   that at atmospheric pressure. Meanwhile, the droplet moved quickly
   downward once it grew to the departure size at atmospheric while the
   droplet exhibited a slow stick-slip motion although it reached the
   departure size at low pressures, which was called the droplet departure
   retention effect. In a growth cycle of condensed droplet, the heat
   transfer process was controlled by the droplet growth rate in small
   surface subcooling range. However, the droplet departure retention
   delayed the surface renewal reducing the effective heat transfer area in
   large surface subcooling range. Furthermore, droplet departure retention
   was introduced to explain the inherent mechanism of the nonlinear
   increasement of heat flux varying with surface subcooling. This work is
   beneficial to clear the controlling mechanisms of dropwise condensation
   heat transfer and offer a new avenue to further enhance heat transfer of
   dropwise condensation at low steam pressure.
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