Abstract:
Dropwise condensation heat transfer on waterrepellent surfaces is inherently linked to the mode of droplet
departure from the surface. When a microgrooved hydrophobic
surface is exposed to condensation, multiple spontaneous droplet
removal pathways for surface renewal are manifested. We present
numerical modeling of dropwise condensation on a microgrooved
hydrophobic surface. Our model is an extension of the wellestablished one-dimensional modeling approach involving estimation of overall condensation heat transfer through the integration of
individual droplet contributions. The model presented here accounts
for all the surface renewal mechanisms observed on the microgrooved hydrophobic surface: growth and coalescence of condensate
droplets within the microgroove and on the ridges, imbibition of the
microgrooves with condensate, bulge formation, spontaneous dewetting of the microgrooves, and shedding of large drops through
gravity. The modeling results show that the microgrooves trigger condensate shedding from the surface much earlier compared to a
planar hydrophobic surface. As a result, the microgrooved hydrophobic surface maintains a much lower area coverage and attains a
significantly higher condensation heat flux compared to a planar surface. The model also enables isolation of the relative
contributions of the four mechanisms, wherein it is observed that the spontaneous dewetting transition of microgrooves dominates
the other mechanisms in terms of the overall surface renewal rate. This is in contrast to the planar hydrophobic surface where droplet
shedding under gravity is the main surface renewal mechanism. Finally, we also evaluate the effect of microgroove geometry on the
condensation heat transfer performance. The model predicts that hydrophobic microgrooves with depth of ∼200 μm and narrow
widths below ∼100 μm can yield enhanced thermal performance.
