A method for controlling absolute pressures at the entrance and exit of a nanochannel/nanotube

A method is proposed to apply specified pressures at the entrance and exit of a nanochannel/nanotube. The pressure at the entrance is controlled by imposing an external force on fluid atoms within the pump region, while the pressure at the exit is adjusted by applying another external force on the piston which is an extension of the back reservoir. The method is validated by simulating argon flowing through a nanochannel/nanotube with different pressures at the ends, and the simulation results show that the pressures can be well controlled by this method. To further test the method in an unsteady case, the external force in the pump region is linearly increased while that on the piston keeps unchanged. The results show that the pressure in the back reservoir keeps constant while the pressure in the front reservoir increases as expected. The end effect on pressure drop for argon flowing through a nanotube is also investigated. Finally, the method has been proven to work effectively for water transport through carbon nanotubes with different diameters and different wall models. The advantage of the method is that it controls the absolute pressures in both the front and back reservoirs continuously and it is more applicable to long nanochannels/nanotubes compared to previous methods.