(473b) Rheological Characterization of Nasa Propellants and Modeling/Simulation of the Mixing Process for Scale-up to Production

A joint effort was conducted between the U.S. Army RDECOM-ARDEC, the Polymer Processing Institute at New Jersey Institute of Technology, and Alliant Techsystems (ATK) / Thiokol Propulsion, to investigate the fluid dynamics of the mixing process for NASA's Space Shuttle Booster Rocket Propellant using modeling and simulations through computer aided computational fluid dynamics supported by laboratory rheological data. Results of the effort will be used as a means to accurately predict scale-up of the mixing process to support production requirements. ATK / Thiokol Propulsion provided drawings of the 8PI (5-gallon) vertical mixer, propellant ingredients and the mixing procedure used in a 1-gallon mixer to ARDEC. A mesh file was created from the mixer drawings using Fluent GAMBIT and the initial conditions from the mixing procedure. Five mixes using combinations of 20µm and 200µm sized particles of Ammonium Perchlorate (AP) were then prepared in the ARDEC Energetics Rheology Laboratory (ERL) using a Thermo Haake torque mixer. A RDA III Dynamic Analyzer was used for Rheological testing. The mix quality from the Thermo Haake experiments was generally good, yielding uniform, homogeneous mixes. The Specific Energy Input increased as the Ammonium Perchlorate (AP) concentration increased. Overall, the Complex Viscosity data generated by the RDA III is generally reproducible with the exception of Mix III. The Complex Viscosity increased as the AP concentration increased. Mixes I and II were found to be near-Newtonian in nature, but exhibited a small slope for viscosity-frequency curve (a weak power-law); Mix III was 100% power-law; while Mix IV and Mix V were typical suspension with higher sensitivity at the lower shear range of 0.1 to 1.0 rad/s, and slight power-law from 1.0 to 100 rad/s. The Complex Viscosity of all five mixes decreased as the temperature increased. The mesh drawing of the mixing vessel and the rheological data were then inputted into POLYFLOW software (computational fluid dynamics) for development of a dynamic model to correlate with the actual laboratory data. The model presents the velocity profile and pressures within the mixing vessel and performs particle tracking so that the progress of the mixing and particle movement can be observed within the vessel. The modeling software will ultimately be used to model the 600-gallon production vertical mixer for projecting the process boundary conditions. ATK / Thiokol Propulsion will verify the model by conducting mixing studies using the production-sized mixer.