Water flow through carbon nanotube junctions as molecular convergent nozzles

Abstract

Molecular dynamics (MD) simulations are conducted for water flow throughcarbon nanotube (CNT) junctions as molecular nozzles. The fluidized pistonmodel (FPM) is employed to drive the inlet flow at streaming velocities of 25 and50 m s−1. Water flow through the CNT junctions is found to undergo an increase in streamingvelocity, a decrease in pressure, and an increase in temperature. Although the difference ofthe upstream velocities does not generally lead to an appreciable density difference in thedownstream CNT, the higher streaming velocity causes the upstream density toincrease. The streaming velocity remains almost constant in the upstream CNT, butincreases dramatically in the junction region. The ratio of downstream to upstreamstreaming velocities increases with the ratio of upstream to downstream crosssection. A higher inlet velocity results in larger acceleration, which is generallymore noticeable at larger cross-sectional ratios, and less prominent in junctionswith smaller cross-sectional ratios. The cross-sectional ratio calculated from theinternal radii of the CNTs based on the oxygen atomic density profile of wateris closer to the ratio of downstream to upstream streaming velocities than thecross-sectional ratio calculated from the radii given by the carbon atomic centres.