Shear viscosity calculation of water in nanochannel: molecular dynamics simulation
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Shear viscosity calculation of water in nanochannel: molecular dynamics simulation Alireza Shadloo-Jahromi1,*, Masoud Kharati-Koopaee2 and Rasoul Khaledialidusti3 Department of Mechanical and Aerospace Engineering, Shiraz University of Technology, Shiraz, Iran 2 Department of Mechanical and Aerospace Engineering, Shiraz University of Technology, Shiraz, Iran 3 Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway (Received December 9, 2019; final revision received April 23, 2020; accepted June 6, 2020) 1
Shear viscosity is one of the important transport properties which affects different phenomena in nanoconfined water. This study aims to investigate the effect of sub-Angstrom variations of nanochannel size on the shear viscosity of water confined in a silicon wall by employing equilibrium molecular dynamics (EMD) simulations. Simulation results demonstrate that water molecules confined in the slits are layered and for channels width less than 21 Å, the number of layers varies from one to six. We show that if the capillary size becomes less than 18.5 Å, the sub-Angstrom variations significantly affect the layered structure of the confined water. This causes the anomalous behavior of water viscosity and therefore, the flow resistance of nanoconfined water. According to the previous studies, the shear viscosity is greatly enhanced for subnanometer capillaries so that the shear viscosity increases dramatically by decreasing the channel size; however, we found that shear viscosity obeys an oscillatory behavior and has a complicated behavior which originates from the consistency between the channel size and the space required to embed one layer of water molecules. Results show that five minima and four maxima values for the viscosity are observed for channels width less than 18.5 Å. Such unfamiliar behavior of viscosity and, consequently, the flow resistance, friction coefficient and slip length should be taken into account in investigation and design of such nanoconfined water. Keywords: MD simulation, nanoconfined water, viscosity, silicon wall
1. Introduction The recent growing interest in fluid flows at nanoscale originates from the evolution of technology that allows the manufacturing of Nanofluidic devices (Abgrall and Nguyen, 2008). To simulate these nanofluidic devices, basic equations of fluid dynamics in macro-scale have been abandoned because of the existence of at least one nanodimension in the nanofluidic systems that alters the behavior of fluid and flow. Experimental studies at the atomic scale are difficult or even impossible to perform; so developing the atomistic simulation technique to study regions that cannot be accessed by experiment is essential. Among all kinds of fluid, water is one of the most important fluids used in industrial processes. Most recent characteristic applications for nanotubes that are closely associated with water involve seawater desalination (Zhao et al., 2012) or drug delivery (
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