Congresos. Editorial UPV
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Congresos realizados en la UPV publicados por la Editorial Universitat Politècnica de València.
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Browsing Congresos. Editorial UPV by Sponsor "Air Force Office of Scientific Research"
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- PublicationAnalytical / Computational Approach to Liquid Spray Heating and Vaporization at Supercritical Pressures(Editorial Universitat Politècnica de València, 2017-07-28) Jorda Juanos, Albert; Sirignano, William; National Science Foundation, EEUU; University of California, Irvine; Generalitat de Catalunya; Air Force Office of Scientific Research[EN] Our findings from two areas of background research will define an approach to the study of liquid spray heating and vaporization in gases at supercritical pressure: (i) vaporizing droplets at supercritical pressure and (ii) supercritical combustion in simple configurations, e.g., counterflow. The a priori conclusion that only one phase exists at supercritical pressure is based on false “lore” and not physical law. The question about the phases must be left open until the analysis reaches a conclusion; a proper approach will be defined. Proper equations of state for density and enthalpy and the determination of phase equilibrium, liquid composition due to dissolved gas, energy of vaporization, surface tension, and transport properties for high pressures will be discussed. The case of an isolated droplet will be reviewed and origin of the transcritical concept will be explained. A counterflow spray configuration at pressures above the liquid critical pressure will be analyzed. The concept of shifting phase equilibrium will be applied as the droplets in the spray heat. Hydrocarbon liquids and oxidizing gaseous environments will be studied. Differences between real fluids and ideal fluids at high pressures will be emphasized. Proper rules for gaseous mixtures and liquid solutions will be discussed.
- PublicationPlane wave irradiation of a layered system: resonance-based control over thermal runaway(Editorial Universitat Politècnica de València, 2019-10-15) Mohekar, Ajit; Tilley, Burt; Yakovlev, Vadim; Air Force Office of Scientific Research[EN] The loss factor of a material is a key characteristic behind heat generation during EM heating. For typical ceramics, the loss factor increases exponentially with temperature potentially initiating thermal runaway which can damage the material through melting or cracking. Equilibrium of EM heating can be represented by a parametric plot of the average steady-state temperature as function of the applied power that is known as a power response curve. In a layered structure, for wavelengths of the incident wave that are much larger than the layer’s thickness, the power response curve is an S-shaped bifurcation diagram (or S-curve). Stable temperatures are low at the lower branch of the S-curve and may be very high (up to ~2000 K) at the upper branch. The recent analytical and numerical models show that, for a triple (lossless-lossy-lossless) layered system, when thickness of the structure is comparable with the wavelength, an electric field resonance can be achieved in the lossy layer. This resonance causes the S-curve to acquire another (middle) stable branch and become a double S-curve. That suggests that temperatures during thermal runaway may be controlled by the field resonance. However, these models assume two-side symmetric irradiation. In this paper, we show that the resonance producing a double S-curve can be achieved in a more practical scenario with one-side irradiation: in the system with a metal plate the resonance is achieve by choosing layer's thickness and triggering a constructive interference of the incident and reflected waves. A series of double S-curves computed with COMSOL Multiphysics are analyzed, and practical ways of controlling thermal runaway in EM heating of layered structures are discussed.