A series of fluid physics microgravity experiments with an enough long run time were performed in the ‘‘KIBO,’’ the Japanese Experiment Module aboard the International Space Station, to examine the transition to chaos of the thermocapillary convection in a half zone liquid bridge of silicone oil with a Prandtl number of 112. The temperature difference between the coaxial disks induced the thermocapillary-driven flow, and we experimentally demonstrated that the flow fields underwent a tran- sition from steady flow to oscillatory flow, and finally to chaotic flow with increasing temperature differ- ence. We obtained the surface temperature time series at the middle of the liquid bridge to quantitatively evaluate the transition process of the flow fields. By Fourier analysis, we further confirmed that the flow fields changed from a periodic, to a quasi-periodic, and finally to a chaotic state. The increasing nonlin- earity with the development of the flow fields was confirmed by time-series chaos analysis. The deter- mined Lyapunov exponent and the translation error indicated that the flow fields made transition to the chaotic field with the increasing temperature difference.
Research Containing: Thermocapillary convection
Dynamic particle accumulation structure (PAS) in half-zone liquid bridge – Reconstruction of particle motion by 3-D PTV
Three-dimensional (3-D) velocity field reconstruction of oscillatory thermocapillary convections in a half-zone liquid bridge with a radius of O (1 mm) was carried out by applying 3-D particle tracking velocimetry (PTV). Simultaneous observation of the particles suspended in the bridge by two CCD cameras was carried out by placing a small cubic beam splitter above a transparent top rod. The reconstruction of the 3-D trajectories and the velocity fields of the particles in the several types of oscillatory-flow regimes were conducted successfully for sufficiently long period without losing particle tracking. With this application the present authors conducted a series of experiments focusing upon the collapse and re-formation process of the PAS by mechanically disturbing fully developed PAS.
Various flow patterns in thermocapillary convection in half-zone liquid bridge of high prandtl number fluid
Various flow patterns induced by a thermocapillary-driven convection in a half-zone liquid bridge of a high Prandtl number fluid (Pr = 0(10)) far beyond the critical condition were investigated experimentally. After the onset of oscillatory convection, one can observe several types of flow patterns with increasing a temperature difference between the both end surfaces of the bridge. The flow patterns were categorized through flow visualization, measurement of surface temperature variation and reconstruction of the pseudo-phase space.
The long-duration fluid physics experiments on a thermocapillary-driven flow have been carried out on the Japanese Experiment Module ‘Kibo’ aboard the International Space Station (ISS) since 2008. In these experiments, various aspects of thermocapillary convection in a half-zone (HZ) liquid bridge of high Prandtl number fluid have been examined under the advantages of the long-duration high-quality microgravity environment. In 2010, the authors succeeded to realize nonlinear convective fields in the HZ liquid bridge of rather high aspect ratio. Special attention was paid on to the complex convective fields, especially on the behaviors of the hydrothermal wave (HTW) over the free surface visualized by an infrared camera. In order to evaluate the characteristics of the nonlinear convective behaviors and their transition processes, the authors indicate the images taken by the infrared camera describing the time evolution of HTW, the spatio-temporal diagram, the Fourier analysis, and the pseudo-phase space, reconstructed from the time series of the scalar information of the liquid bridge, that is, surface temperature variation. In this paper, the authors introduce the signature of complex HTW behaviors observed at the long-duration on-orbit experiments, and make comparisons with some previous terrestrial and microgravity experiments.
Disruption of an Aligned Dendritic Network by Bubbles During Re-melting in a Microgravity Environment
The Pore Formation and Mobility Investigation (PFMI) utilized quartz tubes containing succinonitrile and 0.24 wt% water “alloys” for directional solidification (DS) experiments which were conducted in the microgravity environment aboard the International Space Station (ISS; 2002–2006). The sample mixture was initially melted back under controlled conditions in order to establish an equilibrium solid-liquid interface. During this procedure thermocapillary convection initiated when the directional melting exposed a previously trapped bubble. The induced fluid flow was capable of detaching and redistributing large arrays of aligned dendrite branches. In other cases, rapidly translating bubbles originating in the mushy zone dislodged dendrite fragments from the interface. The detrimental consequence of randomly oriented dendrite arms at the equilibrium interface upon reinitiating controlled solidification is discussed.