1,721,015 research outputs found
Assessment of thermovibrational theory and its application to g-jitter on the Space Station
No full text3D Analysis of crystal/melt interface shape and Marangoni flow instability in solidifying liquid bridges
No full textSolidification of Gallium (Pr=0.02) in liquid bridges in zero gravity conditions is investigated by numerical solutions of the three-dimensional and time-dependent flow-field equations. A single region (continuum) formulation based on the enthalpy method is adopted to model the phase change problem. The paper analyzes the influence of the azimuthally asymmetric and steady first bifurcation of the Marangoni flow on the shape of the solid/melt interface during the crystal growth process. The numerical results show that this interface is distorted in the azimuthal direction. The distortion is related to the sinusoidal three-dimensional temperature disturbances due to the instability of the Marangoni flow. The three-dimensional flow field organization, related to the wave number, changes during the solidification process; this behaviour is explained according to the variation of the aspect ratio of the solidifying liquid bridge. A correlation law is found for the azimuthal wave number of the instability as function of the melt zone aspect ratio
3D Analysis of crystal/melt interface shape and Marangoni flow instability in solidifying liquid bridges
No full textAssessment of thermovibrational theory and its application to g-jitter on the Space Station
No full text
Influence of buoyancy forces on Marangoni flow instabilities in liquid bridges
No full textThe influence of buoyancy forces on oscillatory Marangoni flow in liquid bridges of different aspect ratio is investigated by three-dimensional, time-dependent numerical solutions and by laboratory experiments using a micro-scale apparatus and a thermographic visualisation system. Liquid bridges heated from above and from below are investigated. The numerical and experimental results show that for each aspect ratio and for both the heating conditions, the onset of the Marangoni oscillatory flow is characterized by the appearance of a standing wave regime; after a certain time, a second transition to a travelling wave regime occurs. The three-dimensional flow organization at the onset of instability is different according to whether the bridge is heated from above or from below. When the liquid bridge is heated from below, the critical Marangoni number is larger, the critical wave number (m) is smaller and the standing wave regime is more stable, compared with the case of bridge heated from above. For the critical azimuthal wave number, two correlation laws are found as function of the geometrical aspect ratio A
Three-dimensional numerical simulation of Marangoni instabilities in liquid bridges: influence of geometrical aspect ratio
No full textOscillatory Marangoni convection in silicone oil liquid bridges with different geometrical aspect ratios is investigated by three-dimensional and time-dependent numerical simulations, based on control volume methods in staggered cylindrical non uniform grids. The three-dimensional oscillatory flow regimes are studied and compared with previous experimental and theoretical results. The results show that the critical wave number (m), related to the azimuthal spatio-temporal flow structure, is a monotonically decreasing function of the geometrical aspect ratio of the liquid bridge (defined as ratio of the length to the diameter). For this function a general correlation formula is found, that is in agreement with the previous experimental findings. The critical Marangoni number and the oscillation frequency are decreasing functions of the aspect ratio; however, the critical Marangoni number, based on the axial length of the bridge, does not change much with the aspect ratio. For each aspect ratio investigated, the onset of the instability from the axi-symmetric steady state to the three-dimensional oscillatory one is characterized by the appearance of a standing wave regime that exhibits, after a certain time, a second transition to a travelling wave regime. The standing wave regime is more stable for lower aspect ratios since it lasts for a long time. This behaviour is explained on the basis of the propagation velocity of the disturbances in the liquid phase; for this velocity a general correlation law is found as function of the aspect ratio and of the Marangoni number
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