CFD Analysis on a Vortex Enhanced CVD Reactor Design
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CFD Analysis on a Vortex Enhanced CVD Reactor Design Kazunori Kuwana, Rodney Andrews 1, Eric A. Grulke 2, and Kozo Saito Department of Mechanical Engineering, University of Kentucky, Lexington, KY 40506, USA 1 Center for Applied Energy Research, University of Kentucky, Lexington, KY 40506, USA 2 Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506, USA ABSTRACT To enhance the yield of multi-walled carbon nanotubes (MWNTs), a vortex enhanced CVD reactor (VECVD) design has more advantage over the conventional straight tube CVD. A computational fluid dynamics (CFD) code was applied to analyze heat and mass transfer processes to compare the conventional CVD design performance with a new type. The calculation showed that VECVD has a stronger and more uniform circulation along the reactor than the conventional CVD design.
INTRODUCTION Arrays of aligned carbon nanotubes, where nanotubes are oriented in parallel to each other and perpendicular to growth surface, are of great interest for many potential applications. Because of the excellent electron emission properties of carbon nanotubes, some researchers proposed to utilize aligned carbon nanotubes for flat panel displays and highly efficient media for high harmonic generation [1]. Several groups [1-3] have developed different methods for producing aligned MWNTs using CVD. At the Center for Applied Energy Research at the University of Kentucky, a method for producing bulk quantities of high-purity aligned MWNTs through the catalytic decomposition of a ferrocene-xylene mixture at temperature around 700 °C has been developed [2]. Carbon deposits are formed on both the walls of the quartz furnace tube and flat quartz substrate that was placed within the furnace to act as additional sites for nanotube growth. The growth rate of nanotubes depends on temperature, flow rate, total pressure of feed gas and geometry of reactor. CFD can be used to study on effects of these parameters on the production rate of nanotubes. In addition, CFD is a useful tool to design the optimal geometry of reactor. In the present study, a series of numerical simulations on heat and mass transfer processes in the CVD reactor were performed using a commercial CFD software, Fluent. Based on these numerical results, effects of reactor geometry on the temperature field, velocity field and mass transfer are discussed. Also, a new type of flow-injection and substrate geometry that can enhance the mass transfer to the growth surface was identified.
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NUMERICAL MODEL Figure 1 shows a schematic of the CVD reactor developed at the University of Kentucky. Here, a mixture of ferrocene and xylene was fed continuously into a tubular quartz reactor (diameter, ~ 95 mm; length, ~ 1820 mm), which is heated by a furnace of 700 °C. Carrier gas is argon with 10 % hydrogen, and its flow rate is 6 L/min at room temperature. The numerical model is based on the three-dimensional, steady and compressible fluid flow with temperature-dependent fluid properties. To estimate the ma
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