a b s t r a c tThis paper deals with thermally induced meniscus oscillations in a two-phase system consisting of a liquid plug and a vapor bubble in a capillary tube of circular cross-section. This system represents the simplest version of a heat transfer device called ''pulsating heat pipe" (PHP). Our purpose is to gain fundamental understanding of the physical processes that cause self-sustained thermally driven oscillations. A visualization experiment is performed and the oscillations of the liquid-vapor meniscus and the vapor pressure are observed. We propose next a theoretical model. It differs from existing models by the account of the two-phase equilibrium that occurs locally at the vapor-liquid interface and by introduction of the time varying wetting films through which the major part of the heat and mass transfer occurs.Results from the proposed model show a good agreement with the experiment.

In this paper we present results on parametrically forced gravity waves in a circular cylinder in the limit of large fluid-depth approximation. The phase diagram that shows the stability-forcing-amplitude threshold and the wave-breaking threshold has been determined in the frequency range of existence of the lowest axisymmetric wave mode. The instability is shown to be supercritical for forcing frequencies at and above the natural frequency and subcritical below in a frequency range where the instability and breaking thresholds do not coincide. Above the instability threshold, the growth in wave amplitude is exponential, but with an initial time delay. The wave-amplitude response curve of stationary wave motions exhibits steady-state wave motion, amplitude modulations and bifurcations to other wave modes at frequencies where the parametric instability boundary of the axisymmetric mode overlaps with the neighbouring modes. The amplitude modulations are either on a slow time scale or exhibit period tripling and intermittent period tripling, without wave breaking. In the wave-breaking regime, a finite-time singularity may occur with intense jet formation, a phenomenon demonstrated by others in fluids of high viscosity and large surface tension. Here, this singular behaviour with jet formation is demonstrated for a low viscosity and low kinematic surface tension liquid. The results indicate that the jet is driven by inertial collapse of the cavity created at the wave trough. Therefore, the jet velocity is determined by the wave fluid velocity but depends, in addition, on kinematic surface tension and viscosity as these affect the last stable wave crest shape and the cavity size.

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In this article, a three-dimensional transient numerical approach coupled with fluid-structure interaction for the modeling of an aortic trileaflet heart valve at the initial opening stage is presented. An arbitrary Lagrangian-Eulerian kinematical description together with an appropriate fluid grid was used for the coupling strategy with the structural domain. The fluid dynamics and the structure aspects of the problem were analyzed for various Reynolds numbers and times. The fluid flow predictions indicated that at the initial leaflet opening stage a circulation zone was formed immediately downstream of the leaflet tip and propagated outward as time increased. Moreover, the maximum wall shear stress in the vertical direction of the leaflet was found to be located near the bottom of the leaflet, and its value decreased sharply toward the tip. In the horizontal cross section of the leaflet, the maximum wall shear stresses were found to be located near the sides of the leaflet.

The paper deals with an optimized unified power-quality conditioner (UPQC), which aims at the integration of series active and shunt active power filters with minimum volt-ampere (VA) loading of the UPQC. The series active filter is a dynamic voltage restorer (DVR), which regulates the voltage at the load end with minimum VA loading of the overall UPQC by injecting the voltage at an optimum angle. The proposed scheme is validated by an experimental prototype in the laboratory. Selected experimental results are reported along with analytical findings, which show the effectiveness of the proposed UPQC. Index Terms-Optimum angle voltage injection, unified power-quality conditioner (UPQC), volt-ampere (VA) optimization, voltage sag.

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Experimental investigation of performance of a single phase UPQC for voltage sensitive and non-linear loads.