Validated particle agglomeration models for fireball plasma and fallout products
Abstract
Plasma Chemistry for Nuclear Forensics Fallout from a nuclear blast represents substantial danger because of radioactive particles of different sizes, morphologies, and compositions that contaminate substantial area. In designing systems dealing with nuclear weapons of mass destruction, it is critical to be able to limit the distribution and mitigate the effect of fallout in the areas in vicinity of a blast. Design of counter-WMD systems largely relies on models describing blast effects. Multiple computational codes have been developed predicting formation and transport of fallout particles in the atmosphere. However, the short-term processes occurring in the fireball plasma and generating precursors for the longer term atmospheric agglomeration and transport processes are poorly understood. This research will address these deficiencies and develop a validated predictive tool describing formation of condensed particles and particle agglomerates in the fireball plasma. State-of the art computational algorithms designed to run on GPUs (graphical processor units) will be used to develop physics-based descriptions of processes governing agglomeration of irregularly shaped particulates and particulate clusters in fireball plasmas. A broad range of particle sizes, from microns to millimeters will be covered, and the effects of plasma chemistry, heat transfer, particulate coalescence/agglomeration, transport, and particle charging will be accurately described. The models will be validated by small scale laboratory experiments that generate inert and chemically reacting plasmas by electrostatic discharge. Surrogate particulates with progressively sophisticated morphologies and chemical/ionization reactivity will represent different aspects of agglomeration processes in different tests, in accordance with theoretical models. The developed validated models will be cast into particle number density and size distribution functions that can be used in hydrocodes that model fireball plasmas. Typically, particulates are assumed to behave as spheres in a flow field described by a continuum model. Particulate morphology and fractal dimensions, affecting their behavior substantially, are not accounted for. The limitations of the continuum flow field description for particulates with dimensions comparable to the mean free path of the gas molecules (a finite Knudsen number regime) are neglected. The effect of bow shocks, turbulence, and sharp temperature and concentration gradients around aerosolized particulates on local values of viscosity, thermal diffusivity, mass transfer coefficient, and drag are not typically considered. Processes associated with motion of ionized particles affected by locally distributed charges are omitted. The above shortcomings of the computational models are due to the prohibitive computational cost and lack of reliable ways to tune and calibrate respective models based on reproducible and readily interpretable experimental data. Based on our earlier work of modeling two-phase flows in an inductively coupled plasma, Direct Simulation Monte Carlo (DSMC) calculations will be performed to model the ESD plasma over a broad range of relevant conditions and parameters
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 10, 2017
- Source ID
- HDTRA11710044
Entities
People
- Deborah Ann Levin
Organizations
- Defense Threat Reduction Agency
- University of Illinois Urbana–Champaign