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Analysis of controlled molecular dynamic flow in a channel with non-equal inlet and outlet cross-sectional areas

Najafi H. R., Karimian S. M. H.

Journal of Theoretical and Applied Mechanics

2017

Vol. 55 nr 4

1141--1153

Thermo-fluid properties are required for numerical modeling of nano/micro devices. These properties are mostly obtained from the results of molecular dynamics (MD) simulations. Therefore, efforts have been made to develop methods for numerical evaluation of fluid properties such as pressure and velocity. One of the main challenges faced by numerical simulations is to simulate steady molecular flow in channels with non-equal inlet and outlet boundaries. Currently, periodic boundary conditions at the inlet and outlet boundaries are an inevitable condition in many steady flow molecular dynamics simulations. As a result, a nano-channel with different cross sectional areas at the inlet and outlet could not be simulated easily. Here, a method is presented to generate and control steady molecular flow in a nano-channel with different cross sectional areas at the inlet and outlet. The presented method has been applied to a converging-diverging channel, and its performance has been studied through qualitative and quantitative representation of flow properties.

Analysis of pressure behavior in a temperature controlled molecular dynamic flow

Najafi H. R., Karimian S. M. H.

Journal of Theoretical and Applied Mechanics

2016

Vol. 54 nr 3

881--892

Thermo-fluid properties are required for numerical modeling of nano/micro devices. These properties are mostly obtained from results of molecular dynamics (MD) simulations. Therefore, efforts have been put in developing methods for numerical evaluation of fluid properties, such as pressure. In this paper, the pressure behavior in a controllable nanochannel flow is investigated. The nanoflow field is created by imposing a gradient of a macroscopic property such as temperature. Details of the pressure calculation method in a molecular system and its sensitivity to the approximations made are described first. The effect of temperature rise in a uniform flow on the pressure field is studied next. Then, in the flow under a fixed mean velocity condition, the effect of temperature gradient as a controllable property on the pressure field of nanoflow is studied. Velocity, pressure and molecular density of nanoflows with various temperature gradients and different temperature levels are investigated as well. It has been found that the temperature level at which the temperature gradient is imposed, is important. A fixed temperature gradient will not always lead to the same pressure gradient at different temperature levels. Furthermore, quite interestingly, it is observed that at a fixed temperature gradient, with the variation of mean velocity the pressure field also varies.