Last modified
September 15, 2003

  Seminar Abstract
Center for Data Intensive Computing


 
 


 

Fluid Dynamics Issues in Synthesis of Carbon Nanotubes

We will discuss results of computer simulations, needed computational tools, and fluid physics issues crucial for synthesis of carbon nanotubes (CN). We consider laser ablation (LA), chemical vapor deposition (CVD), and decomposition of high-pressure carbon oxide (HiPco) processes for formation of CN. These processes are controlled by metal catalyst particles that initialize synthesis of carbon nanotubes from feedstock gas.

In the laser vaporization process (LA), the feedstock plume loaded with catalyst particles expands explosively into the background gas. The aim of the study is to find thermal conditions for formation of carbon nanotubes in the laser furnace. The proposed model includes a multi-species formulation for concentration of chemical components combined with compressible Euler equations. To obtain the thermal behavior of catalyst particles the Euler solver has been combined with Lagrangian tracking of catalyst particles. The chamber pressure, its shape, plume emerging velocity, and the periodicity of the plume emerging dramatically affect the thermal behavior of catalyst particles.

In the HiPco process, the catalyst particles enter the HiPco reactor being submerged in carbon oxide jets and are heated up to 1000C in the reactor by means of mixing of steady, high-angle-of-incidence jets. To Fe clusters, which do not act as good catalysts, the catalyst particles should be heated as quickly as possible. The poor performance of the original reactor configuration is explained in terms of features of particle trajectories. Straightforward measures are not sufficient to achieve fast heating because of the behavior of particle trajectories. The proposed way to classify trajectories (path lines) has been applied to optimization of the HiPco process.

Finally, the interaction of a feedstock gas with growing carbon nanotubes in CVD will be considered. The low-Re flow passes through the "bamboo forest" of nanotubes interacting with catalyst particles located at the base of the nanotubes. The sub-micron nanotube diameter leads to higher Knudsen number micro-flow. The effect of slip boundary conditions and the validity of Navier-Stokes equations will be discussed.

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