5 research outputs found
A plate-type condenser platform with engineered wettability for space applications
Vapor condensation is extensively used in applications that demand the
exchange of a substantial amount of heat energy or the vapor-liquid phase
conversion. In conventional condensers, the condensate removal from a subcooled
surface is caused by gravity force. This restricts the use of such condensers
in space applications or in horizontal orientations. The current study
demonstrates proof-of-concept of a novel plate-type condenser platform for
passively removing condensate from a horizontally oriented surface to the
surrounded wicking reservoir without gravity. The condensing surface is
engineered with patterned wettabilities, which enables the continuous migration
of condensate from the inner region of the condenser surface to the side edges
via surface energy gradient. The surrounding wicking reservoir facilitates the
continuous absorption of condensate from the side edges. The condensation
dynamics on different substrates with patterned wettabilities are investigated,
and their condensation heat transfer performance is compared. The continuous
migration of condensate drops from a superhydrophobic to a superhydrophilic
area can rejuvenate the nucleation sites in the superhydrophobic area,
resulting in increased heat transport. We can use the condenser design with
engineered wettability mentioned above for temperature and humidity management
applications in space
Preferred Mode of Atmospheric Water Vapor Condensation on Nanoengineered Surfaces: Dropwise or Filmwise?
Condensing atmospheric water vapor on surfaces is a sustainable approach to addressing the potable water crisis. However, despite extensive research, a key question remains: what is the optimal combination of the mode and mechanism of condensation as well as the surface wettability for the best possible water harvesting efficacy? Here, we show how various modes of condensation fare differently in a humid air environment. During condensation from humid air, it is important to note that the thermal resistance across the condensate is nondominant, and the energy transfer is controlled by vapor diffusion across the boundary layer and condensate drainage from the condenser surface. This implies that, unlike condensation from pure steam, filmwise condensation from humid air would exhibit the highest water collection efficiency on superhydrophilic surfaces. To demonstrate this, we measured the condensation rates on different sets of superhydrophilic and superhydrophobic surfaces that were cooled below the dew points using a Peltier cooler. Experiments were performed over a wide range of degrees of subcooling (10β26 Β°C) and humidity-ratio differences (5β45 g/kg of dry air). Depending upon the thermodynamic parameters, the condensation rate is found to be 57β333% higher on the superhydrophilic surfaces compared to the superhydrophobic ones. The findings of the study dispel ambiguity about the preferred mode of vapor condensation from humid air on wettability-engineered surfaces and lead to the design of efficient atmospheric water harvesting systems
Atmospheric water vapor condensation on engineered interfaces: Busting the myths
Condensing atmospheric water vapor on surfaces is a sustainable approach to
potentially address the potable water crisis. However, despite extensive
research, a key question remains: what is the physical mechanism governing the
condensation from humid air and how significantly does it differ from pure
steam condensation? The answer may help define an optimal combination of the
mode and mechanism of condensation as well as the surface wettability for best
possible water harvesting efficacy. Here we show that this lack of clarity is
due to the differences in heat transfer characteristics during condensation
from pure vapor and humid air environments. Specifically, during condensation
from humid air, the thermal resistance across the condensate is non-dominant
and the energy transfer is controlled by vapor diffusion and condensate
drainage. This leads to filmwise condensation on superhydrophilic surfaces,
offering the highest water collection efficiency. To demonstrate this, we
measured condensation rate on different sets of superhydrophilic and
superhydrophobic surfaces in a wide degree of subcooling (10 - 26 C) and
humidity-ratio differences (5 - 45 g/kg of dry air). The resulting condensation
rate is enhanced by 57 - 333 % on the superhydrophilic surfaces as compared to
the superhydrophobic ones. The findings of this study challenges the nearly
century-old scientific ambiguity about the mechanism of vapor condensation from
humid air. Our findings will lead to the design of efficient atmospheric water
harvesting systems