Water Flows in Copper and Quartz Nanochannels

Numerous experimental results indicate, that the microscale flows are essentially different from flows in large scale [1], [2]. The continuum Navier-Stokes approach, suitable for large sale flows, is not applicable to small scales. At the same time, however, there exists an extension of the Navier – Stokes approach, also based on the assumption of a continuous medium – the micropolar fluid model – which agrees quite well with some experiments in microscale. The micropolar fluid model – proposed by Eringen in 1966 [3] takes into account microrotation of the molecules, different from the local vorticity of the flow. The experiments and theoretical estimations indicate, that for real flows through narrow channels the importance of the micropolar effects grows when the channel width decreases down to the values comparable with the dimensions of the particles of the fluid. However, under such conditions, the assumption of continuous medium, essential for the theory of micropolar fluids, does not seem to be justified. The problem of validity of the micropolar fluid model for the flows through narrow channels is yet to be solved. Some information on the validity of the micropolar model to description of the flows of Cl2 or P5 in narrow channels are given in [4], [5] however these results concern fluids which very rarely flow in microdevices. Moreover, the used molecular model of the channel wall is so simplified, that it cannot simulate any real physical material. Since water is the fluid, most often flowing through microchannels and the channel walls are most often made of silicon, quartz or copper, we concern ourselves to water flows in copper and quartz channels. We compare the theoretical predictions for flow velocity and microrotation with results of molecular dynamics simulations of flows under gravity field down rectangular channels.