MAE 298 SEMINAR: Self-Heating, Thermal Ignition and Explosions

Abstract: Explosions are a consequence of interplay of chemical or nuclear reactions, motion of material and molecular transport (diffusion) of energy and species in chemically reactive materials. Explosions proceed in stages, beginning with a self-heating or initiation process that results in the growth of reaction rates through feedback with energy releasing reactions and multiplication of reactive species. If the self-heating process results in an uncontrolled or runaway reaction this will culminate in igniting a combustion process. The combustion process can take the form of smoldering, fire, a deflagration (subsonic) or detonation (supersonic) wave; events that are most often associated with explosions. I will describe the history and engineering science behind these concepts and describe recent efforts in our laboratory to experimentally quantify hot surface ignition thresholds. I will present an analysis of the results of experiments and numerical simulations using the framework of classical analytical theory of self-heating pioneered by Frank-Kamenetskii and Zel’dovich. Based on these results, we demonstrate that ignition thresholds can be correlated in terms of critical thermal gradients near hot surfaces for a variety of configurations.

Bio: Joe Shepherd is the C. L. “Kelly” Johnson Professor of Aeronautics and Professor of Mechanical Engineering at the California Institute of Technology in Pasadena, CA. He has been on the faculty at Caltech since 1993 and served on the faculty of Rensselaer Polytechnic Institute from 1986 to 1993. Prior to that, he was a staff member at Sandia National Laboratories from 1980 to 1986. He earned his doctorate in applied physics from Caltech in 1981, and his bachelor's degree in physics from the University of South Florida in 1976. Shepherd's research interests have primarily been in the application of molecular and atomic physics, statistical thermodynamics, chemical kinetics, fluid dynamics and solid mechanics to various aspects of combustion, shock and detonation waves, and high-speed flows. His approach is to combine laboratory experimentation using imaging and other optical methods with analytical and numerical studies to obtain fundamental insights into nature and technology. During his career, he has worked on a number of projects to investigate and improve the safety of nuclear power plants and waste storage or treatment facilities in the United States, Europe and Asia, including the 1979 incident at Three Mile Island and the 2011 incidents at Fukushima Dai-ichii. His group carried out extensive research on aircraft fuel tank flammability, developing methods of characterizing ignition sources and characterizing explosive events. Researchers in the Explosion Dynamics Laboratory have made fundamental contributions to the study of detonation waves, hypersonic flow, thermal and other ignition processes, and response of piping systems to detonations and shock waves.

Personal website: http:/shepherd.caltech.edu/

Research group website: http://shepherd.caltech.edu/EDL/