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Research Papers: Heat Transfer in Manufacturing

Numerical Investigation of Thermofluid Flow in a Chemical Vapor Deposition Furnace Utilized to Manufacture Template-Synthesized Carbon Nanotubes

[+] Author and Article Information
Yashar Seyed Vahedein

Department of Mechanical Engineering,
Rochester Institute of Technology,
76 Lomb Memorial Drive,
Rochester, NY 14623
e-mail: ys5978@rit.edu

Michael G. Schrlau

Department of Mechanical Engineering,
Rochester Institute of Technology,
76 Lomb Memorial Drive,
Rochester, NY 14623
e-mail: mgseme@rit.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received October 28, 2015; final manuscript received May 15, 2016; published online June 7, 2016. Assoc. Editor: Wilson K. S. Chiu.

J. Heat Transfer 138(10), 102101 (Jun 07, 2016) (12 pages) Paper No: HT-15-1680; doi: 10.1115/1.4033643 History: Received October 28, 2015; Revised May 15, 2016

Template-based chemical vapor deposition (TB-CVD) is a versatile technique for manufacturing carbon nanotubes (CNTs) or CNT-based devices for various applications. In this process, carbon is deposited by thermal decomposition of a carbon-based precursor gas inside the nanoscopic cylindrical pores of anodized aluminum oxide (AAO) templates to form CNTs. Experimental results show that CNT formation in templates is controlled by TB-CVD process parameters, such as time, temperature, and flow rate. However, optimization of this process is done empirically, requiring tremendous time and effort. Moreover, there is a need for a more comprehensive and low cost way to characterize the flow in the furnace in order to understand how process parameters may affect CNT formation. In this report, we describe the development of four, 3D numerical models (73 < Re < 1100), each varying in complexity, to elucidate the thermofluid behavior in the TB-CVD process. Using computational fluid dynamic (CFD) commercial codes, the four models are compared to determine how the presence of the template and boat, composition of the precursor gas, and consumption of species at the template surface affect the temperature profiles, velocity fields, mixed convection, and strength of circulations in the system. The benefits and shortcomings of each model, as well as a comparison of model accuracy and computational time, are presented. Due to limited data, simulation results are validated by experiments and visual observations of the flow structure whenever possible. Decent agreement between experimental data and simulation supports the reliability of the simulation.

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Figures

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Fig. 1

Schematic representations of the TB-CVD system. (a) Schematic depicting the physical TB-CVD system. Purge, carrier, and precursor gases are metered into a three-stage tube furnace consisting of temperature-controlled heaters. Carbon is deposited on the templates, which are positioned in the center of the heated region. (b) Schematic depicting the geometric features and segments of the tube furnace and placement of the boat and templates. Segments B–D represent the heated region of the tube furnace.

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Fig. 2

Schematic representation of the boundary conditions for the TB-CVD tube furnace. Boundary conditions only pertaining to model M-4 are indicated with single asterisks (*). Boundary conditions pertaining to the species concentration are indicated with double asterisks (**).

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Fig. 3

Model mesh structure of the TB-CVD tube furnace. Reference point of coordinate system is located at the center of the tube wall above the inlet, where the x-axis coincides with the tube centerline. (a) Perspective view of the model mesh structure near the boat and templates inside the tube furnace. (b) Two-dimensional projected view of the 3D mesh near the inlet, showing boundary layer meshing near the walls.

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Fig. 4

Contours of axial, transverse, and vertical velocity components in the middle cross section of the tube furnace. Contours for all four models are presented as a function of flow rate.

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Fig. 5

Velocity vector plots in the axial cross section of the tube furnace for model M-4. Plots show the magnitude, direction, and evolution of the longitudinal vortices as a function of flow rate.

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