Friday, October 2 • 2:30 PM – PWEB, Rm. 175

Thermofluidic and interfacial dynamics of spark-ignited metallic droplets

Dr. Sukalyan Bhattacharya

Texas Tech University

Abstract: In the first part of this talk, an intriguing experimental observation is discussed where highspeed imaging captures thermofluidic dynamics of spark-ignited nano Aluminum powder. The phenomenon consists of initial detachment, subsequent pulsation, occasional fragmentation and eventual explosion of molten metallic masses separated from the original bulk resting on a copper plate. We provide a phenomenological description elucidating every aspect of the entire process. The key consideration in constructing the explanation is recognition of the anomalous frequency value of interfacial oscillation of the metallic droplets revealing important details of their opaque interior. This leads to the second part of the talk where a novel theory shows how wave features at a drop surface can be exploited to quantify size and position of bubbles or solid particles inside the liquid domain. Such in-vivo diagnostic capability has similarity to atomic spectroscopy or application of Bragg’s law in crystallography, and can be useful in a wide range of fields including combustion technology and material processing. •

Biographical Sketch: Dr. Bhattacharya received his Ph.D. in Mechanical Engineering from Yale University in 2005. Prior to that, he obtained his Bachelor’s degree from Jadavpur University in 1997, and obtained his Master’s degree at University of Connecticut in 2000. Upon Ph. D. graduation, he joined the Department of Mechanical Engineering at Texas Tech University as an assistant professor, and became an associate professor in 2011. His research interest includes low Reynolds number hydrodynamics, turbulence, turbulent scalar transport, and statistical mechanics.

For additional information, please contact Prof. Xinyu Zhao at (860) 486-0241, xinyuz@engr.uconn.edu or Laurie Hockla at (860) 486-2189, hockla@engr.uconn.edu

Friday, September 25 • 2:30 PM – PWEB, Rm. 175

Combustion: From a Jet Engine to an Exploding Star

Dr. Alexei Poludnenko

Naval Research Laboratory

Abstract: Turbulent reacting flows are pervasive both in our daily lives on Earth and in the Universe. They power the modern society being at the heart of many energy generation and propulsion systems, such as gas turbines, internal combustion and jet engines. On astronomical scales, thermonuclear turbulent flames are the driver of some of the most powerful explosions in the Universe, knows as Type Ia supernovae. These are crucibles, in which most of the elements around us from oxygen to iron are synthesized, and in the last 20 years they have led to one of the most remarkable discoveries in modern science, namely of the existence of dark energy. Despite this ubiquity in Nature, turbulent reacting flows remain poorly understood still posing a number of fundamental questions. In this talk, an overview of the numerical and theoretical work at the Naval Research Laboratory over the recent years is given, aimed at studying both chemical and thermonuclear turbulent flames. Several surprising phenomena that have emerged in the course of this work will be highlighted, in particular, in the context of the intrinsic instabilities of high-speed turbulent reacting flows, as well as some of the outstanding open challenges. Finally, the implications of this work for the development of the next generation of accurate, predictive turbulent flame models required for the design of practical combustion applications will be briefly discussed.

Biographical Sketch: Dr. Poludnenko received his Ph.D. in Physics and Astronomy from the University of Rochester in 2004. Upon graduation, he joined the Department of Energy ASC Flash Center at the University of Chicago as a postdoctoral researcher, where he worked on theoretical studies of astrophysical supernovae explosions and numerical modeling of thermonuclear deflagrations and detonations. Since joining the Naval Research Laboratory in 2007 first as a National Research Council postdoctoral fellow and later as a permanent research staff member, Dr. Poludnenko has been working on a wide range of topics in combustion, numerical algorithm development for hydro- and magnetohydrodynamics, and high-performance computing. In recent years, he has been leading the research program at NRL focused on theoretical and computational studies of turbulent combustion in chemical and astrophysical systems.

Friday, September 18 • 2:30 PM – IMS, Rm. 20

Can Other Materials Besides Diamond have Ultrahigh Thermal Conductivity?

David A. Broido

Professor of Physics Boston College, Chestnut Hill, Massachusetts

Abstract: Diamond and its carbon cousins, graphite and graphene, have long been known to have by far the highest thermal conductivities (κ) of any materials, achieving room temperature values of over 2000 Wm-1 K-1 . Other ‘high κ’ materials such as copper (κ=400 Wm-1 K-1 ) have significantly lower values. In spite of welldefined criteria to guide the search for new high κ materials, little progress has been made over the years. In this talk, I will describe a novel paradigm for achieving high κ that we have recently proposed. This paradigm introduces new criteria, which stem from fundamental vibrational properties that occur in compounds where the constituent atoms have a large mass ratio. We have calculated the lattice thermal conductivities of candidate materials using a first principles theoretical approach that combines an exact solution of the Boltzmann transport equation for phonons with accurate determination of the harmonic and anharmonic interatomic forces from density functional theory. We have demonstrated excellent agreement with the measured thermal conductivities of a wide range of materials, validating the predictive capability of this theory and contributing insight into the nature of thermal transport in materials. Guided by the new paradigm, we have identified one material, cubic boron arsenide, that should have an exceptionally high room temperature κ comparable to the highest known bulk value achieved in diamond. This finding opens opportunities for controlling phonon thermal transport, which may facilitate the design of new high κ materials for thermal management applications.

Biographical Sketch: David Broido is currently a Professor of Physics at Boston College. He received his Ph.D. degree in Theoretical Physics from the University of California at San Diego in 1985. He was a National Research Council Postdoctoral Fellow at the U.S. Naval Research Laboratory before coming to Boston College in 1987. He is a Fellow of the American Physical Society. His research interests include theoretical studies of thermal and thermoelectric transport properties of materials using first principles approaches. https://www.bc.edu/schools/cas/physics/people/david_broido

Friday, September 11 • 2:30 PM – PWEB, Rm. 175

Computational Fluid dynamics modeling of industrial-scale fires

Dr. Ning Ren

Fire Hazard and Protection Group FM Global

Abstract: Fire is one of the major causes of property loss. According to the National Fire Protection Association, more than ten billion dollars in fire-induced property damage are incurred annually in the US alone. Understanding fire behavior and improving the design of fire suppression systems are critical steps that can lead to the reduction of fire losses. To this end, fire testing at different physical scales has historically been used at FM Global to provide engineering fire protection solutions/guidelines. In recent years, however, much of this testing has been carried out using computational fluid dynamics (CFD)- based numerical modeling. A novel open-source fire modeling CFD tool has been developed by FM Global (firefoam) and it is designed for modeling the complex interactions of fire related phenomena such as buoyancy driven turbulence/combustion, flame radiation, condensed-phase pyrolysis, sprinkler spray and film flow transport, and suppression. The availability of a fire simulation tool, such as FireFOAM, can not only provide fundamental physical insights into fire dynamics and suppression, but also help design large-scale fire tests more effectively and efficiently. Moreover, numerical modeling can be used to explore some challenging practical scenarios where testing may be difficult, if not impossible, to conduct. In this talk, two numerical studies will be presented to illustrate the use of CFD modeling in fire loss prevention. The first configuration consists of a Class 2 rack storage array, a standard fuel and storage arrangement that is used for the purposes of commodity classification as well as the evaluation of fire protection systems. The second case corresponds to a storage configuration of vertically stacked paper rolls, which is a typical fire hazard in the pulp and paper industry. Details on various sub-models, including pyrolysis, turbulent flow, and flame heat transfer will be presented. Modeling results for two rack storage configurations (3- and 5-tier high) and two roll paper configurations (2- and 3-roll high) will be compared to available experimental data. Modeling results for two additional configurations (7-tier high rack storage and 6-roll high roll paper), for which no experimental data are available, will also be provided.

Biographical Sketch: Dr. Ren obtained his B.S. in Fire Safety Engineering from University of Science & Technology of China (USTC) in 2005, M.S. in Fire Protection Engineering in 2007 and Ph.D. in Mechanical Engineering in 2010 from University of Maryland – College Park (UMD). He was a postdoctoral associate at Department of Fire Protection Engineering at UMD from 2011 to 2012, before joining FM Global as a senior research scientist. He works on fire suppression modeling using Largeeddy simulation based fire simulator. His research area includes pyrolysis modeling, flame extinction and suppression modeling.

For additional information, please contact Prof. Xinyu Zhao at (860) 486-0241, xinyuz@engr.uconn.edu or Laurie Hockla at (860) 486-2189, hockla@engr.uconn.edu

Wednesday, June 24 • 1:30 PM – Biology/Physics Building (BPB), Rm. 130

Designing Shape Memory Materials for Damping, Actuation, and Energy Applications

Ying Chen

Assistant Professor of Materials Science and Engineering Rensselaer Polytechnic Institute, Troy, NY

Abstract: Shape memory alloys have the remarkable capability to switch between two “programmed” geometries upon the application and removal of stimuli such as stress, heat, or magnetic field. Their shape memory properties result from a diffusionless and crystallographically reversible martensitic phase transformation that occurs by shear. However, many polycrystalline shape memory alloys are limited by their inherent brittleness caused by severe stress concentration at grain boundaries during martensitic transformations. In this talk, I will present two strategies that we have developed to overcome this limitation. I will discuss our recent work on small scale oligocrystalline alloys with bamboo grain structures, and potential technological developments that can result from our understanding of the small-scale properties and size effects. When bulk polycrystalline structures are desirable, we design dual-phase alloys in which a ductile nontransforming second phase is precipitated along grain boundaries to cushion the grain boundaries and alleviate stress concentrations. Oligocrystalline and polycrystalline shape memory alloys with excellent shape memory properties and mechanical durability are promising for many damping, actuation, and energy applications.

Biographical Sketch: Dr. Ying Chen earned her B.S. in Materials Science and Engineering from Tsinghua University in Beijing, China in 2004 and Ph.D. in Materials Science and Engineering from MIT in 2008. She was a postdoctoral associate at the MIT Institute for Soldier Nanotechnologies from 2008 to 2010, before joining GE Global Research Center in Niskayuna, NY as a materials scientist. She worked on high temperature superalloys at GE GRC for a little over a year, and then joined the Rensselaer faculty at the end of 2011. Her research focuses on elucidating microstructure-mechanical property relationships in metallic materials using both experimental and mesoscale modeling approaches.

For additional information, please contact Prof. Michael T. Pettes at (860) 486-2855, pettes@engr.uconn.edu or Laurie Hockla at (860) 486-2189, hockla@engr.uconn.edu

Wednesday, June 10 • 1:30 PM – Biology/Physics Building (BPB), Rm. 130

Electronic Transport in Topological Insulator Nanostructures

Luis A. Jauregui

Postdoctoral Associate, Philip Kim Group Department of Physics, Harvard University, Cambridge, MA

Abstract: I will describe our recent transport experiments on topological insulator materials such as Bi2Te3 and BiSbTeSe2 nanoribbons (TINRs). We were able to successfully distinguish the bulk and surface carriers. The experiments have particularly revealed a list of unique transport signatures of the spin-helical, Dirac fermion topological surface states, and provide ways to access and utilize such surface states in novel topological quantum devices. Topological insulators (TI) are gapped band insulators in the bulk, but have nontrivial, “topologically protected”, spin-helical conducting states with gapless Dirac fermion dispersion on the surface. Such “topological surface states” are considered promising platforms to explore various novel physics ranging from quantum anomalous Hall effect, Majorana fermions to excitonic condensation. However, electronic transport of topological surface states in real TI materials is easily obscured by competing conduction channels that include the bulk as well as the “conventional” 2D electron gas (2DEG) formed by band bending at the surface. This is a major challenge in current experiments and device applications involving topological insulators. In this talk, I will describe our recent electron transport experiments on TI materials based on Bi2Te3 and BiSbTeSe2. We have explored ways to reduce the bulk conduction, and revealed a list of unique electronic transport signatures of the spin-helical, Dirac fermion topological surface states. In addition, we have also measured induced superconductivity in TINRs. These experiments may facilitate better access and control of TI surface states to explore the more exotic physics and applications in topological quantum devices.

Biographical Sketch: Dr. Luis Jauregui earned his B.S. in Electrical Engineering from National University of Engineering in Lima, Peru in 2007 and his Ph.D. in the area of micro and nanotechnology from the Department of Electrical and Computer Engineering at Purdue University in 2015. He was the recipient of the Intel Ph.D. fellowship for the years 2012 – 2013 and the Purdue Research Foundation Fellowships 2013 – 2015. Currently, he is a postdoctoral associate in the Department of Physics at Harvard University. His research focuses on experimental investigations of electron transport in low dimensional systems like nanowires, and two dimensional layered materials.

For additional information, please contact Prof. Michael T. Pettes at (860) 486-2855, pettes@engr.uconn.edu or Laurie Hockla at (860) 486-2189, hockla@engr.uconn.edu