OPTIMISING ACOUSTIC RESONATORS FOR SONOFUSION EXPERIMENTS WITH EVOLUTIONARY ALGORITHMS

The sizing of simple resonators like guitar strings or laser mirrors is directly connected to the wavelength and represents no complex optimisation problem. This is not the case with liquid-filled acoustic resonators of non-trivial geometries, where several masses and stiffnesses of the structure and the fluid have to fit together. This creates a scenario of many competing and interacting resonances varying in relative strength and frequency when design parameters change. Hence, the resonator design involves a parameter-tuning problem with many local optima. As its solution evolutionary algorithms (EA) coupled to a forced-harmonic FE simulation are presented. A new hybrid EA is proposed and compared to two state-of-theart EAs based on selected test problems. The motivating background is the search for better resonators suitable for sonofusion experiments where extreme states of matter are sought in collapsing cavitation bubbles

A new mechanistic model of critical heat flux in forced-convection subcooled boiling

Because of its practical importance and various industrial applications, the process of subcooled flow boiling has attracted a lot of attention in the research community in the past. However, the existing models are primarily phenomenological and are based on correlating experimental data rather than on a first-principle analysis of the governing physical phenomena. Even though the mechanisms leading to critical heat flux (CHF) are very complex, the recent progress in the understanding of local phenomena of multiphase flow and heat transfer, combined with the development of mathematical models and advanced Computational Fluid Dynamics (CFD) methods, makes analytical predictions of CHF quite feasible. Various mechanisms leading to CHF in subcooled boiling have been investigated. A new model for the predictions of the onset of CHF has been developed. This new model has been coupled with the overall boiling channel model, numerically implemented in the CFX 4 computer code, tested and validated against the experimental data of Hino and Ueda. The predicted critical heat flux for various channel operating conditions shows good agreement with the measurements using the aforementioned closure laws for the various local phenomena governing nucleation and bubble departure from the wall. The observed differences are consistent with typical uncertainties associated with CHF data

Mechanistic analysis of loft pulsed neutron activation data

Pulsed Neutron Activation (PNA) is a technique for measuring mass-weighted flow velocities without perturbing the flow. Monte Carlo PNA tagging and Monte Carlo detection calculations of the irradiated fluid with the transport of the irradiated fluid are used to predict the time spectrum in a PNA measurement. This mechanistic method has been used to analyze recent LOFT PNA measurements of single-phase water flowing in a 14-in. (0.35 m) schedule 160 steel pipe

The Use Of Fractal Techniques For Flow Regime Identification

[No abstract available]174545552Ben Mizrachi, Procaccia, Grassberger, Characterization of experimental (noisy) strange attractors (1984) Physical Review A, 29 A, pp. 975-977Feder, (1988) Fractals, , Plenum Press, New YorkGrassberger, Procaccia, Measuring the strangeness of strange attractors (1983) Physica, 500, pp. 189-208Hagiwara, Experimental studies on chaotic behavior of liquid film flow in annular two-phase flows (1988) PhysicoChem. Hydrodynam., 10, pp. 135-147Hubbard, Dukler, The characterization of flow regimes for horizontal two-phase flow (1966) Proc. Heat Transfer and Fluid Mechanics Institute, , Stanford Univ. Press, Stanford, CalifJones, Zuber, The interrelation between void fraction fluctuations and flow patterns in two-phase flow (1975) Int. J. Multiphase Flow, 2, pp. 273-306Lin, Hanratty, Detection of slug flow from pressure measurements (1987) Int. J. Multiphase Flow, 13, pp. 13-21Mandelbrot, (1982) The Fractal Geometry of Nature, , Freeman, New YorkMatsui, Identification of flow regimes in vertical gas liquid two-phase flow using differential pressure fluctuation (1984) Int. J. Multiphase Flow, 10, pp. 711-720Matsui, Automatic identification of flow regimes in vertical two-phase flow using differential pressure fluctuations (1986) Nucl. Engng Des., 95, pp. 221-231Moon, (1987) Chaotic Oscillations, , Wiley-Interscience, New YorkTutu, Pressure fluctuations and flow pattern recognition in vertical two-phase gas-liquid flow (1982) Int. J. Multiphase Flow, 8, pp. 443-447Tutu, Pressure drop fluctuations and bubble-slug transition in a vertical two-phase water flow (1984) Int. J. Multiphase Flow, 10, pp. 211-216Vince, Lahey, Jr, On the development of an objective flow regime indicator (1982) Int. J. Multiphase Flow, 8, pp. 93-12

Mechanistic modeling of CHF in forced-convection subcooled boiling

Because of the complexity of phenomena governing boiling heat transfer, the approach to solve practical problems has traditionally been based on experimental correlations rather than mechanistic models. The recent progress in computational fluid dynamics (CFD), combined with improved experimental techniques in two-phase flow and heat transfer, makes the use of rigorous physically-based models a realistic alternative to the current simplistic phenomenological approach. The objective of this paper is to present a new CFD model for critical heat flux (CHF) in low quality (in particular, in subcooled boiling) forced-convection flows in heated channels