Fangzhu(方诸) : an ancient Chinese nanotechnology for water collection
from air: history, mathematical insight, promises and challenges
Abstract
Fangzhu, which has been lost for thousands of years, is an ancient
device for water collection from air, its mechanism is unknown yet. Here
we elucidate its possible surface-geometric and related physical
properties by the oldest the Yin-Yang contradiction. In view of modern
nanotechnology, we reveal that Fangzhu’s water-harvesting ability is
obtained through a hydrophilic-hydrophobic hierarchy of the surface,
mimicking spider web’s water collection, lotus or desert beetle’s water
intake. The convex-concave hierarchy of Fangzhu’s textured surface
enables it to have low wettability(high geometric potential) to attract
water molecules from air through the nano-scale convex surface and
transfer the attracted water along the concave surface to the collector.
A mathematical model is established to reveal three main factors
affecting its effectiveness, i.e., the air velocity, the surface
temperature and surface structure. The lost technology can play an
extremely important role in modern architecture, ocean engineering,
transportation and others to catch water from air for everyday use.