Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session A5: Reacting Flows: General |
Hide Abstracts |
Chair: Douglas Kelley, University of Rochester Room: 104 |
Sunday, November 22, 2015 8:00AM - 8:13AM |
A5.00001: Inside out: Speed-dependent barriers to reactive mixing Douglas Kelley, Thomas Nevins Reactive mixing occurs wherever fluid flow and chemical or biological growth interact over time and space. Those interactions often lead to steep gradients in reactant and product concentration, arranged in complex spatial structures that can cause wide variation in the global reaction rate and concentrations. By simultaneously measuring fluid velocity and reaction front locations in laboratory experiments with the Belousov-Zhabotinsky reaction, we find that the barriers defining those structures vary dramatically with speed. In particular, we find that increasing flow speed causes reacted regions to move from vortex edges to vortex cores, thus turning the barriers ``inside out''. This observation has implications for reactive mixing of phytoplankton in global oceans. [Preview Abstract] |
Sunday, November 22, 2015 8:13AM - 8:26AM |
A5.00002: A Gibbs Formulation for Reactive Materials with Phase Change D. Scott Stewart A large class of applications have pure, condensed phase constituents that come into contact, chemically react and simultaneously undergo phase change. Phase change in a given molecular material has often been considered to be separate from chemical reaction. Continuum modelers of phase change often use a phase field model whereby an indicator function is allowed to change from one value to another in regions of phase change, governed by evolutionary (Ginzburg-Landau) equations, whereas classic chemical kinetics literally count species concentrations and derive kinetics evolution equations based on species mass transport. We argue the latter is fundamental and is the same as the former, if all species, phase or chemical are treated as distinct chemical species. We pose a self-consistent continuum, thermo-mechanical model to account for significant energetic quantities with correct molecular and continuum limits in the mixture. A single stress tensor, and a single temperature is assumed for the mixture with specified Gibbs potentials for all relevant species, and interaction energies. We discuss recent examples of complex reactive material modeling, drawn from thermitic and propellant combustion that use this new model. [Preview Abstract] |
Sunday, November 22, 2015 8:26AM - 8:39AM |
A5.00003: Propagation of symmetric and non-symmetric lean hydrogen flames in narrow channels: influence of heat losses Carmen Jimenez, Vadim Kurdyumov Direct numerical simulations, including detailed chemistry and transport, are used to investigate the structure and stability of freely propagating lean hydrogen flames in planar narrow channels. Depending on the flame burning rate and the wall properties, the flame-wall heat exchange can result in flame extinction. For large heat losses only the fastest burning flames, corresponding to fast reactant flowing rates can propagate. We show that double flame solutions, symmetric and non-symmetric, can coexist for the same set of parameters. The symmetric solutions are calculated imposing symmetric boundary conditions in the channel mid-plane and when this restriction is relaxed non-symmetric solutions develop. This indicates that the symmetric flames are unstable to non-symmetric perturbations, as predicted before within the context of a constant density model. Moreover, the burning rates of the non-symmetric flames are found to be significantly larger than those of the corresponding symmetric solution and therefore the range of conditions for flame extinction and flashback also differ. This shows that assuming in CFD that the flame should reproduce the symmetry of the cold flow can have important safety implications in micro scale combustion devices burning lean hydrogen mixture. [Preview Abstract] |
Sunday, November 22, 2015 8:39AM - 8:52AM |
A5.00004: Fluid-Plasma Coupling in Hydrogen Flames Luca Massa, Jonathan Retter, Nick Glumac, Gregg Elliot, Jonathan Freund Recent experiments show that hydrogen diffusion flames at low Reynolds number can be markedly affected by a dielectric barrier discharge (DBD) plasma. The flame surface deforms and flattens, and light emissions increase. We develop a simulation model to analyze the mechanisms that causes these changes, and apply it to numerical calculations of axisymmetric flames with co-annular DBD, matching the corresponding experiments. Body forces due to charge sheaths are found to be the main mechanism, with radicals produced by plasma excitation playing a secondary role for the present conditions. The non-actuated flame flickers at approximately 10 Hz, in good agreement with the experiments. As the DBD voltage is increased, the flame flattens and oscillations decrease, eventually ceasing above a threshold value. The fully flattened case has a stoichiometric surface lying flat across the fuel orifice, with flame temperature exceeding significantly the adiabatic flame value. A force based on a linearized plasma sheath model, calibrated against air experiments, reproduces the main features of the experiments and provides a good estimate for the threshold flattening potential. In faster flowing regimes, radical production by the plasma becomes more important. [Preview Abstract] |
Sunday, November 22, 2015 8:52AM - 9:05AM |
A5.00005: Supersonic Particle Impacts: Cold Spray Deposition of Polymeric Material Trenton Bush, David Schmidt, Jonathan P. Rothstein When a solid, ductile particle impacts a substrate at sufficient velocity, the resulting heat, pressure, and plastic deformation at the interface can produce bonding. The use of a supersonic gas flow to accelerate such particles is known as Cold Spray deposition. The Cold Spray process has been commercialized for some metallic materials, but further research is required to unlock the exciting material properties possible with polymeric compounds. In this work, we present a combined computational and experimental study whose aim is to define the necessary flow conditions for a convergent-divergent de Laval nozzle to produce successful bonding in a range of polymers. From our initial exploration of temperature-pressure space, we will reveal a material dependent `window of deposition' where successful deposition is possible. Furthermore, we will present our computational work on the development of an optimized nozzle profile that maximizes particle total energy (kinetic plus thermal) upon impact and thus maximizes the likelihood of successful deposition. These predictions will be confirmed by the experimental results presented. [Preview Abstract] |
Sunday, November 22, 2015 9:05AM - 9:18AM |
A5.00006: SPIV study of two interactive fire whirls Katherine Hartl, Alexander Smits Fire whirls are buoyancy-driven standing vortex structures that often form in forest fires. Capable of lifting and ejecting flaming debris, fire whirls can hasten the spread of fire lines and start fires in new places. Here we study the interaction of two jets in an externally applied circulation as an introduction to the study of two interacting fire whirls. To study this interaction we use two burner flames supplied with DME and induce swirl by entraining air through a split cylinder that surrounds both burners. Three components of velocity are measured using Stereo Particle Image Velocimetry both inside and outside the fire whirl core, at the base, midsection, and above the top of the fire whirls. The effects on the height and circulation on the distance between the burners, the rate of fuel supplied to the burners, and the gap size, are examined. [Preview Abstract] |
Sunday, November 22, 2015 9:18AM - 9:31AM |
A5.00007: System Modeling for Ammonia Synthesis Energy Recovery System Gabriela Bran Anleu, Pirouz Kavehpour, Adrienne Lavine An ammonia thermochemical energy storage system is an alternative solution to the state-of-the-art molten salt TES system for concentrating solar power. Some of the advantages of this emerging technology include its high energy density, no heat losses during the storage duration, and the possibility of long storage periods. Solar energy powers an endothermic reaction to disassociate ammonia into hydrogen and nitrogen, which can be stored for future use. The reverse reaction is carried out in the energy recovery process; a hydrogen-nitrogen mixture flowing through a catalyst bed undergoes the exothermic ammonia synthesis reaction. The goal is to use the ammonia synthesis reaction to heat supercritical steam to temperatures on the order of 650$^{\circ}$C as required for a supercritical steam Rankine cycle. The steam will flow through channels in a combined reactor-heat exchanger. A numerical model has been developed to determine the optimal design to heat supercritical steam while maintaining a stable exothermic reaction. The model consists of a transient one dimensional concentric tube counter-flow reactor-heat exchanger. The numerical model determines the inlet mixture conditions needed to achieve various steam outlet conditions. [Preview Abstract] |
Sunday, November 22, 2015 9:31AM - 9:44AM |
A5.00008: Uphill diffusion and phase separation in partially miscible multicomponent mixtures Ping He, Ashwin Raghavan, Ahmed Ghoniem The partially miscible multicomponent mixtures, which are frequently encountered in green chemistry processes, often exhibit complicated behaviors, and are critical to the production rate, energy efficiency, and pollution controls. Recent studies have been mainly focused on phase behaviors. However, the coupled phase equilibrium and transport process, which may be the answer to phase separations observed in experiments, is not well researched. Here, we present a numerical and theoretical study on coupled mixing of heavy oil and supercritical water, and the results of our state-of-art modeling agree with experimental measurements. We find that due to the non-ideal diffusion driving force, (1) strong uphill diffusion of heavy oil fractions occurs, (2) a new heavy oil phase is separated starting from the plait point, and heavy fractions become highly concentrated, and (3) water diffusion initially overshoots in oil, and is expelled lately. Finally, we conclude our analysis applicable to different molecules and conditions. [Preview Abstract] |
Sunday, November 22, 2015 9:44AM - 9:57AM |
A5.00009: Wind Tunnel Testing of a Hydrogen Jet in a Turbulent Crossflow Altered by a Dielectric Barrier Discharge Ryan Fontaine, Jonathan Retter, Jonathan Freund, Nick Glumac, Gregory Elliott It has been demonstrated that plasmas can fundamentally alter the combustion process. The radical production can decrease combustion timescales and the body force produced by the driving electric currents can improve fuel/oxidizer mixing and alter the shape of the steady state flame. We study these mechanisms for a fuel jet exhausting into a well-characterized turbulent cross-flow of air acted upon by a Dielectric Barrier Discharge (DBD) plasma produced at the jet exit. The fuel is hydrogen diluted in cases with N$_{2}$ and Ar. Laser breakdown provides the energy deposition for ignition above the jet. The likelihood of sustained ignition for various fuel compositions and cross-flow conditions is considered along with flame properties once ignited both under the influence of the DBD plasma and without. Additionally, the effect of the DBD on flame blow-off is investigated. The jet is varied from low-momentum ratios ($\sim$ 10$^{-4})$ to high ($\sim$ 1) to alter the relative contributions of the body forces and radical production on the combustion process. This system is studied to quantify the effect of the DBD plasma and discover opportunities for control. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700