Browsing by Author "Yuan, H."
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Item A Simplified Model for Linear and Nonlinear Processes in Thermoacoustic Prime Movers. Part I. Model and linear theory(The Journal of the Acoustical Society of America, 1997-12) Watanabe, M.; Prosperetti, Andrea; Yuan, H.A simplified quasi-one-dimensional model of thermoacoustic devices is formulated by averaging the conservation equations over the cross section. Heat transfer and drag effects are introduced by means of suitable coefficients. While the primary motivation for this work is the development of a model approximately valid in the nonlinear regime, the focus of this paper is the proper formulation of the transfer coefficients and the analysis of the linear problem. The accuracy of the model is demonstrated by comparison with existing more precise theories and data. Examples of devices with variable cross section demonstrate the flexibility of the approach.Item A Simplified Model for Linear and Nonlinear Processes in Thermoacoustic Prime Movers. Part II. Nonlinear Oscillations(The Journal of the Acoustical Society of America, 1997-12) Yuan, H.; Karpov, Sergey; Prosperetti, AndreaThe simplified quasi-one-dimensional model of thermoacoustic devices formulated in Part I [Watanabe et al., J. Acoust. Soc. Am. 102, 3484–3496 (1997)] is studied in the nonlinear regime. A suitable numerical method is described which is able to deal with the steep waveforms that develop in the system without inducing spurious oscillations, appreciable numerical damping, or numerical diffusion. The results are compared with some experimental ones available in the literature. Several of the observed phenomena are reproduced by the model. Quantitative agreement is also reasonable when allowance is made for likely temperature nonuniformities across the heat exchangers.Item Gas-Liquid Heat Transfer in a Bubble Collapsing Near a Wall(The Physics of Fluids, 1997-01) Yuan, H.; Prosperetti, AndreaThe collapse of a gas bubble near a solid wall is studied numerically by assuming the liquid to be incompressible and the Mach number of the gas flow to be small. The liquid motion is simulated by a boundary integral method and the gas thermo?fluid dynamics by finite differences on a boundary?fitted grid. With the physical properties of a liquid monopropellant, it is found that the liquid heating is essentially localized in the microjet, but is probably not sufficient to cause spontaneous ignition. The reasons for this conclusion — that, while being in general agreement with available experimental evidence, is at variance with deductions from previous spherical collapse calculations — are elucidated.Item Growth and collapse of a vapor bubble in a narrow tube(The Physics of Fluids, 5/4/2000) Ory, E.; Yuan, H.; Prosperetti, Andrea; Popinet, S.; Zaleski, S.The fluid mechanical aspects of the axisymmetric growth and collapse of a bubble in a narrow tube filled with a viscous liquid are studied numerically. The tube is open at both ends and connects two liquid reservoirs at constant pressure. The bubble is initially a small sphere and growth is triggered by a large internal pressure applied for a short time. After this initial phase, the motion proceeds by inertia. This model simulates the effect of an intense, localized, brief heating of the liquid which leads to the nucleation and growth of a bubble. The dimensionless parameters governing the problem are discussed and their effects illustrated with several examples. It is also shown that, when the bubble is not located at the midpoint of the tube, a net flow develops capable of pumping fluid from one reservoir to the other. The motivation for this work is offered by the possibility to use vapor bubbles as actuators in fluid-handling microdevices.Item The Oscillations of Gas Bubbles in Tubes: Experimental Results(The Journal of the Acoustical Society of America, 1999-08) Geng, X.; Yuan, H.; Oguz, H.N.; Prosperetti, AndreaAn experimental study is presented of the frequency dependence and damping of the forced volume oscillations of gas bubbles in liquid-filled tubes. The bubbles occupy the entire section of the tube and are driven by a needle attached to a loudspeaker cone. The liquids used were water, a water–surfactant solution, and silicon oil, and the tube diameters were 1 and 3 mm. The results are in excellent agreement with the theory developed in two earlier papers. This work is motivated by the possibility of using gas bubbles as actuators in fluid-handling microdevices.