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ANSYS 19.2 Release Highlights

Leveraging Simulation to Manufacture Boron Nitride Nanotubes

American Boronite Corporation used ANSYS Fluent computational fluid dynamics (CFD) simulation to develop an advanced process to manufacture boron nitride nanotubes (BNNTs) in continuous yarn and seamless tape formats. This advanced material has many unique mechanical, thermal and electronic properties that can be used in a variety of applications ranging from radiation shielding to solar cells. In the past, BNNTs have been synthesized on a small scale using methods that include ball milling and plasma discharge. With the help of simulation, Boronite has developed a scalable, proprietary, large-scale process with integration of synthesis, processing and quality control systems to ensure high throughput and consistent properties.

Boronite uses an atmospheric pressure chemical vapor deposition (CVD) system to produce and collect the boron nitride nanotubes into a stringy, cotton-like raw material (the "sock") that is then manipulated into the tape and yarn formats as it leaves the CVD reactor. The nanotubes are synthesized in a 1300-1500°C furnace and must be processed immediately after synthesis to improve material properties. The whole reactor and harvesting area must be sealed and kept in an inert environment (oxygen- and water-free) due to the high reactivity of the gases in the reactor. ANSYS Fluent has been an integral tool for modeling the fuel injector as well as the yarn spinning and tape collection systems.

Fuel Injector Modeling

Our injector system uses a mixture of gases and fuel which must be exposed to controlled heating patterns to ensure proper reaction kinetics. Furthermore, the temperature gradients created by this heating can cause stress on the reactor and lead to unwanted eddies which influence nanotube alignment. ANSYS Fluent allows Boronite to efficiently model many variables at once, combining multiphase behavior and compressible turbulent flow with radiative and conductive heat transport. This allows us to optimize reaction parameters and test out new injector prototypes before deploying them in our process.

A visualization of the streamlines flowing from the gas injection points (left) down the reactor and colored by temperature. Rapid heating of gases causes concentric eddies as the gas mixture travels

Spinner Modeling

ANSYS simulations have also been a very useful tool for designing and debugging our yarn spinning prototypes. The transient behavior of the nanotube sock as it travels into the spinning system is important to predict and control the properties. In one of our systems, the material travels into a high speed rotating conical extractor that creates a high shear boundary layer that applies torque to the nanotube sock and creates eddies that push the sock out of the reactor (both phenomena can be seen in the pictures below). The geometry of the extractor and gas flow rates were iterated in ANSYS Fluent simulations to determine the optimal configuration for material production.

Two spinning extractor configurations showing one half of the axisymmetric extractor, with a pressure heat map and velocity vectors. The left shows single phase flow and the right shows the nanotube sock modeled as a stationary permeable membrane.

In both cases, the simulations have given us new perspectives for process development and engineering. The ANSYS Startup Program has allowed us to develop and optimize our brand-new process, becoming the first in the world to produce BNNTs in continuous forms. Not only have we lowered our development time, but we have improved the production efficiencies, reducing overall costs for our advanced materials.