Issue 25/2015 - New progress in the research of nanointerfaces with efficient condensation heat transfer

Since its inception, the condensed microdroplet self-driving nano-bionic interface has attracted great attention from the scientific community and industry, because this new heat and mass transfer interface can be used to design and develop high-performance phase-change-based thermal control devices to meet the growing heat dissipation needs of electronic devices, develop more energy-saving and environmentally friendly heat pumps/air conditioning radiators, and develop other new energy-saving thermal control systems
。 As we all know, droplet condensation is a more efficient energy transport method than film condensation, discrete condensate droplets not only have lower thermal resistance than continuous liquid films, but also can release more surface sites for more frequency of nucleation-growth-fusion-dispersion and more effective phase change heat
transfer.
However, condensate droplets have high interface adhesion on ordinary smooth metal surfaces, and must grow to the millimeter scale to slide away under gravity, which leads to their own thermal resistance is still too high, the frequency of renewal and the residence density are too low
.
In principle, the construction of a new type of condensing microdroplet self-driving nano-bionic functional film on the metal surface can greatly improve
the heat transfer coefficient of droplet condensation.
Different from the traditional droplet condensation mode driven away by gravity, the condensing droplet self-driving mode is driven by the excess surface energy released by its own fusion, without the assistance
of any external force such as gravity and steam shear.
However, how to obtain this novel high-efficiency droplet condensation heat transfer nanointerface experimentally and reveal its potential structure-property relationship is still a challenge, and so far there are few
studies.

Recently, the research team of Gao Xuefeng, Suzhou Institute of Nanotechnology, Chinese Academy of Sciences has made new progress
in the research of copper-based high-efficiency droplet condensation heat transfer nanointerfaces.
They first used electrochemical deposition to construct ultra-thin nickel nanocones in situ on the surface of copper, and after chemical modification with low surface energy, the surface showed extraordinary self-dissociation renewal and high-density nucleation performance
of small-scale condensate microliquids.
Preliminary thermal characterization has confirmed that this nanostructure can achieve an 89%
increase in the heat transfer coefficient of droplet condensation on copper-based surfaces.
In addition, they also proposed a strategy
to greatly improve the heat transfer coefficient of droplet condensation by constructing clustered prismatic nanoneedles in situ on the copper surface 。 Using high-resolution environmental scanning electron microscope and high-speed high-resolution optical imager, they studied the interaction between condensate droplets and nanointerfaces in depth and combined with theoretical analysis, they found that this microscopic three-dimensional rough clustered prismatic nanoneedle can not only realize the high-density nucleation of condensed droplets, but also form spherical suspended droplets of condensate grown in different micro-region limits through the growth mode of "self-transport-self-expansion" or "single self-expansion".
These droplets then self-pop off
by fusing with each other to release excess surface energy.
Preliminary thermal tests have shown that the drop-like condensation heat transfer coefficient on the surface of this nanomaterial can be improved by at least 125%
compared to smooth copper.
In principle, any nanostructure with microscopic three-dimensional roughness and extremely low solid-liquid interface adhesion is expected to be used on metal surfaces, achieving a significant improvement
in the heat transfer efficiency of droplet condensation.
These findings will help the design and development of nanointerface materials and thermal control devices
for efficient heat and mass transfer.
(Ping)