Yixin Zhang

PhD Student, University of Warwick

I obtained my masters degree on thermofluids engineering in July 2017 and bachelors degree on aircraft power engineering in July 2015, both from Harbin Institute of Technologu in China.

In October 2017 I have joined the MNF group as a PhD student majoring in fluid mechanics at University of Warwick. My current research direction is studying rupture and stability of thin liquid films on substrates. 

Research Gate Link

Nanowire liquid pumps

This fascinating video is from a paper titled "Nanowire liquid pumps" published in Nature Nanotechonology. It demonstrated that the outer surface of a nanowire is able to transport liquid. When liquid flows on the surface, it can flow as the thin film flows or the discrete beads. The former flow can be described by the well-known thin film instability while the latter is due to Rayleigh-Plateau Instability. In the thin-film instability, a minimum thickness of the thin film is achieved due to the repulsive intermolecular forces, which prevents the breakup of the thin film. This paper also shows that there is a critical film thickness of ∼10 nm separating two flow mechanisms.

 

 

Why does superfluid helium creep up surfaces?

Helium, which turns into liquid at about 4.2 Kelvin, can be held in a container like a beaker due to gravity. But when it is cooled further to below approximately 2 Kelvin, it creeps up the surface of the beaker and leak. At this temperature, liquid helium is called as superfluid due to its odd properties. For example, the liquid's viscosity becomes nearly zero. Because of that, the fluid can flow very easily even as a result of the smallest pressure. On one hand, a thin liquid helium film will appear as the liquid wet the surface of the beaker. On the other hand, liquid helium has smaller dielectric permittivity than any other medium (except vapour), which results in a negative Hamaker constant and a repulsive van der Waals force across the film. This will act to thicken the film and make the liquid helium flow from the bottom of the beaker to its surface and thus leak. 

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