Enhancement
in heat-transfer performance via dropwise condensation
on superhydrophobic surfaces is much greater than that realized via
generic condensation on a regular surface. However, if the supersaturation
level during condensation increases above a specific value, water
may seep to greater depths between structures. This may lead to attached
condensation, which reduces condensation heat-transfer efficiency
below that of ordinary surfaces. Therefore, it is critical to avoid
the occurrence of supersaturation when superhydrophobic surfaces are
employed in condenser design. The proposed study presents a simple
method for regulating supersaturation on the laboratory scale. Experiments
concerning droplet behavior on a superhydrophobic plate were performed
to investigate droplet detachment and attachment in accordance with
the surface and droplet temperatures. Results obtained have been represented
as a ″droplet-behavior map″, which clearly depicts boundaries
dividing the detachment and attachment regions. The supersaturation
threshold obtained from the said map has been compared against results
obtained from condensation heat-transfer experiments performed in
an actual condenser environment. As observed, the two results demonstrate
excellent agreement. Although superhydrophobicity of surfaces remains
unchanged at room temperature, changes may occur in the extent of
the supersaturation section, which improves condensation heat-transfer
performance, depending on the surface-structure complexity. Therefore,
droplet-behavior mapping has been used in this study to determine
the available supersaturation section in accordance with the variation
in surface roughness. Results confirm that the available supersaturation
region increases with increasing surface roughness and structural
complexity. Therefore, prior to applying superhydrophobicity to condensers,
droplet-behavior mapping must be performed to avoid operation under
the supersaturation conditions, which causes attached condensation.
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