Effects of impact velocity on pressure-driven nanofluid.

Using molecular dynamics simulations, we investigate the pressure-driven water infiltration behavior of carbon nanotubes (CNTs), in which water molecules can infiltrate into CNTs from outside upon an external impact load. According to the direction of impact mechanical wave, the infiltration procedure can be divided into the forward stage (stage I) and the reflected stage (stage II). At the forward stage of mechanical wave, the flow behavior strongly depends on the impact velocity but it is essentially not very sensitive to the tube radius. With a higher impact velocity, the water flow has a higher transport velocity, a lower density, a weaker CNT-water interaction, a higher potential energy, and a more disordered structure shown by a wider distribution of water dipole and OH bonds orientations. At the reflected stage, due to the impact pressure effect, the water structure is significantly changed, and the flow behavior is less sensitive to the impact velocity but more sensitive to the tube radius. After the reflected wave passed the water molecules inside CNTs, the water density and potential are significantly increased, which initiates a significant change for the water structure inside CNTs, especially for small size tubes. In a small tube like (10,10), a new water conformation is created in the reflected procedure, while there is no such new structure created in a larger tube like (20,20). Due to the different structures, the behavior of the pressure-driven water flow inside CNTs is significantly different than the steady flow.