posted on 2016-01-19, 00:00authored byDion S. Antao, Solomon Adera, Yangying Zhu, Edgardo Farias, Rishi Raj, Evelyn N. Wang
Capillary assisted passively pumped
thermal management devices
have gained importance due to their simple design and reduction in
energy consumption. The performance of these devices is strongly dependent
on the shape of the curved interface between the liquid and vapor
phases. We developed a transient laser interferometry technique to
investigate the evolution of the shape of the liquid–vapor
interface in micropillar arrays during evaporation heat transfer.
Controlled cylindrical micropillar arrays were fabricated on the front
side of a silicon wafer, while thin-film heaters were deposited on
the reverse side to emulate a heat source. The shape of the meniscus
was determined using the fringe patterns resulting from interference
of a monochromatic beam incident on the thin liquid layer. We studied
the evolution of the shape of the meniscus on these surfaces under
various operating conditions including varying the micropillar geometry
and the applied heating power. By monitoring the transient behavior
of the evaporating liquid–vapor interface, we accurately measured
the absolute location and shape of the meniscus and calculated the
contact angle and the maximum capillary pressure. We demonstrated
that the receding contact angle which determines the capillary pumping
limit is independent of the microstructure geometry and the rate of
evaporation (i.e., the applied heating power). The results of this
study provide fundamental insights into the dynamic behavior of the
liquid–vapor interface in wick structures during phase-change
heat transfer.