Multiscale Modeling of Carbon Nanotube Bundle Agglomeration inside a Gas Phase Pyrolysis Reactor
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Multiscale Modeling of Carbon Nanotube Bundle Agglomeration inside a Gas Phase Pyrolysis Reactor Guangfeng Hou1*, Vianessa Ng1, Chenhao Xu1, Lu Zhang2, Guangqi Zhang1, Vesselin Shanov1, David Mast3, Wookyun Kim1, Mark Schulz1†, Yijun Liu1 1
Department of Mechanical and Materials Engineering, University of Cincinnati, OH 45221, United States 2 Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, CA 90095, United States 3 Department of Physics, University of Cincinnati, OH 45221, United States ABSTRACT Carbon nanotube (CNT) sock formation is required for the continuous synthesis of CNT thread or sheet using the gas phase pyrolysis method. Nanometer diameter CNTs form and are carried along the reactor tube by gas flow. During the flow, the CNT stick to each other and form bundles of about 10-100 nm diameter. Coupling of the CNT bundles in the flow leads to the formation of a centimeter diameter CNT sock with a wall that is hundreds of nanometers thick. Understanding the multiscale phenomena of sock formation is vital for optimizing the CNT synthesis and manufacturing process. In this work, we present a multiscale model for the CNT bundle agglomeration inside a horizontal gas phase pyrolysis reactor. The interaction between CNT bundles was analyzed by representing the attraction forces between CNTs using a discrete phase modeling method. Flow in the synthesis reactor was studied using a computational fluid dynamics (CFD) technique with multiphase flow analysis. A model was proposed to represent the coupling between CNT bundles and the gas flow. The effect of different CNT bundles on the agglomeration phenomenon was analyzed. The modeling results were also compared with experimental observations. INTRODUCTION Carbon nanotubes (CNTs) are being widely used in various engineering application areas such as electronics [1], composites [2-3], biosensors [4], and in the energy fields [5]. There are also large efforts toward the commercialization of CNT materials [6-7]. Among the CNT synthesis methods, the gas phase pyrolysis technique (also called floating catalyst method) holds high promise for large-scale production due to its ability for continuous synthesis. During the gas phase pyrolysis synthesis process, an aerogel-like sock [8-9] forms inside the reactor, which is critical for successful collection of CNT sheet and yarn. The CNT sock has a multiscale hierarchical structure, and it is formed from a large number of CNT bundles. These bundles are composed of individual CNTs held together due to van der Waals attractions. There are several studies discussing the agglomeration mechanism of these CNT bundles [10-13]. However, there are no attempts to model this agglomeration process directly. Detailed modeling and analysis of
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Corresponding author. Email: [email protected]. Corresponding author. Email: [email protected].
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