Interdisciplinary Applied Mathematics

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Effect of Channel Width


The density oscillations    in    the    channel    also    depend    on    the    channel    width.


Somers and Davis investigated the variation of density profiles in slit channels of different widths ranging from 2.0a to 8.0a (Somers and Davis, 1992). Figure 10.6 shows the density profiles obtained with various channel widths. The results indicate that for channel widths that can accommodate integral fluid layers, e.g., 2a, 2.75a, and 4a, distinct peaks in the density profile are observed. For channel widths, such as 2.25a and 3.25a, the channel is wide enough to accommodate distinct fluid layers: hence additional layers begin to develop, and the new layers appear at channel widths of 2.5a and 3.5a. When the channel width is 8a, seven distinct peaks are observed, and as the channel width increases further, more peaks are observed, but these additional peaks are much weaker compared to the peaks very close to the channel wall. For channels wider than 10a, the fluid layers near the wall are independent of the channel width, and the fluid in the central portion of the channel behaves more like a bulk fluid.


Effect of Fluid Flow


The fluid flow is found to have negligible effect on the density distribution. (Bitsanis et al., 1987) conducted simulations on Couette flow in a nanometer-slit pore    using shear    rates    of    1010    to 1011    s-1    and    found    that


the density distribution is not significantly influenced by the flow; i.e., the density profile in the channel in the presence of bulk transport of fluid is the same as that obtained from an equilibrium MD simulation. This result was also verified by other reported MD simulations. Since experimental techniques or real processes that deal with fluid flow in nanopores are likely to employ smaller shear rates than those that were employed in MD, we can conclude that    in simple    fluids    the    density    profile    will    be    the    equilibrium

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