Molecular Dynamics Study of Friction Reduction of Two-Phase Flows on Surfaces Using 3D Hierarchical Nanostructures

Abstract

The use of superhydrophobic surfaces is one the most promising methods for reducing the friction and increasing the flow rate in fluid transfer systems. Because in such systems the surface structure plays a key role, in this study, we explore the performance of the hierarchical nanostructures. These nanostructures are inspired by the superhydrophobic surface of the lotus leaf. We consider a flow between two walls with hierarchical nanostructures and simulate the system via the molecular dynamics method. The size of the nanostructures and the distance between them have been studied to find whether a design with a maximum flow rate exists. The nanostructures have two parts, a bigger part on the wall which is a half-sphere and a smaller part which is a cylinder on top of the bigger part. Twenty-four different nanostructures are placed on the two walls and three different distances are selected. The effect of wall materials was also examined by considering four different materials, namely, carbon, silicon, and two other hypothetical materials. In the second part of this study, a two-phase flow consisting of water and air have been simulated to study the effect of the trapped airs in the performance. The results show that in the carbon-made walls for the design with minimum pressure drop, the slip length increases by 97% and the flow rate increases by 200%. The increases for silicon-made walls and similar sizes are 99 and 183%, for the slip length and the flow rate, respectively. The slip length for carbon-made walls is almost 3 times larger than the silicon-made walls. Finally, by increasing the air fraction up to 30% in the carbon-made walls, the slip length increases by 430% and the flow rate increases by 310%, and also, for the silicon-made walls, the increases are 380 and 360% for the slip length and the flow rate, respectively.

Multiscale simulations of nanofluidics: Recent progress and perspective

“…Currently, try to increase the mass transport in nanochannels through changing the slip length has been an important subject of a growing number of studies. By constructing nanostructures on channel surfaces, both the contact area between the fluid and the solid wall as well as the surface wettability can be changed, accompanied by the adjusted slip length 190,191 . It was reported that a nanochannel with densely fluorous surface exhibits ultrafast water permeation flux, which is two orders of magnitude greater than those of aquaporins and carbon nanotubes 192 …”

A Comprehensive Review of Wetting Transition Mechanism on the Surfaces of Microstructures from Theory and Testing Methods

“…There are numerous methods that can be used to simulate the droplet states on superhydrophobic surface. From the microscale state, molecular dynamics (MD) study the flow behavior of statistical fluid from the perspective of molecular atoms to explore the wetting state transition of droplets at molecular scale [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. The simulation dynamics are sometimes given by the Monte Carlo method.…”

Recent Developments of Superhydrophobic Surfaces (SHS) for Underwater Drag Reduction Opportunities and Challenges

“…The existence of optimal nanostructure layout at maximum flow rate is also worth further exploration. Saleki et al [71] used lotus leaf nanostructures as the research model to explore the existence of the layout of nanostructure corresponding to the maximum flow rate by simulating the flow between hierarchical nanostructures. Experiments confirm that the maximum flow rate does exist in the designed nanochannel.…”