FLUID FLOW IN NANOTUBES - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 211

Most liquid's molecules have a diameter of about 0.1 nm. Each molecule of
the fluid is “squeezed” on all sides by neighboring molecules and for a period of
time (10 -10 -10 -13 ) fluctuates around certain equilibrium position, which itself from
time to time is shifted in distance commensuration with the size of molecules or
the average distance between molecules l cp :
,
where, n 0 - Numberof molecules per unitvolume of fluid; N A -Avogadro's number;
r -fluid density; m -molar mass.
Estimates show that one cubic of nano water contains about 50 molecules.
This gives a basis to describe the mass transfer of liquid in a nanotube-based
continuum model. However, the specifics of the complexes, consisting of a finite
number of molecules, should be kept in mind. These complexes, called clusters
in literatures, are intermediately located between the bulk matter and individual
particles(atoms or molecules). The fact of heterogeneity of water is now experi-
mentally established [27].
There are groups of molecules in liquid as “microcrystals” containing tens or
hundreds of molecules. Each microcrystal maintains solid form. These groups of
molecules or “clusters”exist for a short period of time, then break up and are re-
created again. Besides, they are constantly moving so that each molecule does not
belong at all times to the same group of molecules, or “cluster.”
Modelingpredicts that gas moleculesbounce off theperfectly smoothinner
walls of thenanotubesasbilliard balls, andwater moleculesslide overthemwithout
stopping. Possible cause of unusually rapid flow of water is maybe due to the
small-diameter nanotube molecules move on them orderly, rarely colliding with
each other. This “organized” move is much faster than usual chaotic flow. How-
ever, while the mechanism of flow of water and gas through the nanotubes is not
very clear and only further experiments and calculations can helpunderstand it.
The model of mass transfer of liquid in a nanotube proposed in this research is
based on the availability of nanoscale crystalline clusters in it [19].
A similar concept was developed by researchers in which the model of struc-
tured flow of fluid through the nanotube is considered. It is shown that the flow
character in the nanotube depends on the relation between the equilibrium crystal-
lite size and the diameter of the nanotube.
Figure 4.11 shows the resultsof calculationsby the molecular dynamicsof fluid
flowin the nanotubein a plane (a)andthree-dimensional state (b).The figure show-
sthe ordered regionsof the liquid.