A flame structure approach for controlling carbon nanotube growth in flame synthesis

Abstract

Flame synthesis of carbon nanotube (CNT) is still not commercialized due to the difficult control over CNT growth region in heterogeneous flame environment. In the present study, a model for flame synthesis of CNT that is capable of predicting CNT growth region is developed using a coupled computation of a computational fluid dynamics (CFD) flame model and a CNT growth rate model. The CFD results serve as input for the growth rate model to calculate CNT length and to generate flame structures that feature high CNT growth regions. Validation of the flame model, CNT growth model, and multi-scale model of flame synthesis is done with good accuracy. In the baseline case, the mixture fraction-based flame structures at various flame heights interestingly suggest a fixed range of mixture fraction of 0.46 to 0.85 within the growth region. The said finding indicates that mixture fraction governs the growth region in a diffusion flame. Almost twofold increase in the size of CNT growth region in physical space is observed when the inlet oxygen composition is increased from 25 to 35%. The increase in heat release of the rich flame at high oxygen concentration provides a wider region of high temperature for growth compared to that at low oxygen concentration.