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Research Containing: Fluid flow

Oscillatory cellular patterns in three-dimensional directional solidification

by on 22 August 2016in Biology & Biotechnology, Physical Sciences No comment

We present a phase-field study of oscillatory breathing modes observed during the solidification of three-dimensional cellular arrays in microgravity. Directional solidification experiments conducted onboard the International Space Station have allowed us to observe spatially extended homogeneous arrays of cells and dendrites while minimizing the amount of gravity-induced convection in the liquid. In situ observations of transparent alloys have revealed the existence, over a narrow range of control parameters, of oscillations in cellular arrays with a period ranging from about 25 to 125 min. Cellular patterns are spatially disordered, and the oscillations of individual cells are spatiotemporally uncorrelated at long distance. However, in regions displaying short-range spatial ordering, groups of cells can synchronize into oscillatory breathing modes. Quantitative phase-field simulations show that the oscillatory behavior of cells in this regime is linked to a stability limit of the spacing in hexagonal cellular array structures. For relatively high cellular front undercooling (i.e., low growth velocity or high thermal gradient), a gap appears in the otherwise continuous range of stable array spacings. Close to this gap, a sustained oscillatory regime appears with a period that compares quantitatively well with experiment. For control parameters where this gap exists, oscillations typically occur for spacings at the edge of the gap. However, after a change of growth conditions, oscillations can also occur for nearby values of control parameters where this gap just closes and a continuous range of spacings exists. In addition, sustained oscillations at to the opening of this stable gap exhibit a slow periodic modulation of the phase-shift among cells with a slower period of several hours. While long-range coherence of breathing modes can be achieved in simulations for a perfect spatial arrangement of cells as initial condition, global disorder is observed in both three-dimensional experiments and simulations from realistic noisy initial conditions. In the latter case, erratic tip-splitting events promoted by large-amplitude oscillations contribute to maintaining the long-range array disorder, unlike in thin-sample experiments where long-range coherence of oscillations is experimentally observable.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/26565251

DECLIC, First Results On Orbit

by on 22 August 2016in Physical Sciences No comment

DECLIC is a multi-user facility to investigate critical fluids behaviour and directional solidification of transparent alloys, developed in the frame of a joint NASA/CNES research program. The instrument is a miniaturized thermo optical laboratory in which one can plug inserts containing the materials to be studied.

Related URLs:
https://cadmos.cnes.fr/sites/default/files/migration/automne/standard/2014_10/p8782_a528d45ac3dd0799d3fe13b58fdaf027IAC_10_A2_5_1.pdf

Transition to chaotic thermocapillary convection in a half zone liquid bridge

by on 22 August 2016in Biology & Biotechnology, Physical Sciences

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.

Related URLs:
http://www.sciencedirect.com/science/article/pii/S0017931015005323

Weightless experiments to probe universality of fluid critical behavior

by on 22 August 2016in Physical Sciences No comment

Near the critical point of fluids, critical opalescence results in light attenuation, or turbidity increase, that can be used to probe the universality of critical behavior. Turbidity measurements in SF6 under weightlessness conditions on board the International Space Station are performed to appraise such behavior in terms of both temperature and density distances from the critical point. Data are obtained in a temperature range, far (1 K) from and extremely close (a few muK) to the phase transition, unattainable from previous experiments on Earth. Data are analyzed with renormalization-group matching classical-to-critical crossover models of the universal equation of state. It results that the data in the unexplored region, which is a minute deviant from the critical density value, still show adverse effects for testing the true asymptotic nature of the critical point phenomena.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/26172640

Experimental elaboration of liquid droplet cooler-radiator models under microgravity and deep vacuum conditions

by on 22 August 2016in Physical Sciences, Technology Development & Demonstration

The basic results of space tests of liquid droplet cooler radiator models as the main elements of frameless systems for low grade heat rejection are considered. The studies carried out have been analyzed and intermediate elaboration’s results are summarized, which concern (1) the development of generators of drop let propellant flows, (2) revealing an operational behavior of fluid collectors of various types and analysis of unsolved problems associated with droplet collection upon the open trajectory’s section passage, and (3) pro vision of the coolant circulation contour’s closing. The necessity is substantiated for the activization of works directed to carrying out space experiments with improved radiator models and new promising propellants in order to provide a possibility of creating new space power plants characterized by megawatt power levels.

Related URLs:
http://link.springer.com/article/10.1134%2FS0040601515130066#/page-1

EFFECT OF THERMAL DRIFT ON THE INITIAL TRANSIENT BEHAVIOR IN DIRECTIONAL SOLIDIFICATION OF A BULK TRANSPARENT MODEL ALLOY

by on 22 August 2016in Biology & Biotechnology, Physical Sciences No comment

In situ monitoring of directional solidification experiments on a transparent model alloy was carried out under low gravity in the Directional Solidification Insert of the Device for the Study of Critical Liquids and Crystallization (DECLIC-DSI) on-board the International Space Station. The present work is focused on the analysis of the interface recoil and its macroscopic shape evolution. Theoretically the interface movement is due to the formation of a solute boundary layer in front of the interface. However, the bulk configuration and the thermal specificities of transparent systems induce thermal effects, which are usually not observed in the classical thin sample configuration. Numerical thermal modeling highlights two thermal contributions to the interface recoil, both increasing with pulling rate. The Warren and Langer model is modified to take into account these contributions that modify the interface dynamics, and a good agreement is obtained between the experiments and the modified model.

Related URLs:
http://onlinelibrary.wiley.com/doi/10.1002/9781119274896.ch3/summary

Spatiotemporal dynamics of oscillatory cellular patterns in three-dimensional directional solidification

by on 22 August 2016in Biology & Biotechnology, Physical Sciences No comment

We report results of directional solidification experiments conducted on board the International Space Station and quantitative phase-field modeling of those experiments. The experiments image for the first time in situ the spatially extended dynamics of three-dimensional cellular array patterns formed under microgravity conditions where fluid flow is suppressed. Experiments and phase-field simulations reveal the existence of oscillatory breathing modes with time periods of several 10’s of minutes. Oscillating cells are usually noncoherent due to array disorder, with the exception of small areas where the array structure is regular and stable.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/23767735

Final Report for Intravenous Fluid Generation (IVGEN) Spaceflight Experiment

by on 9 June 2015in Technology Development & Demonstration No comment

NASA designed and operated the Intravenous Fluid Generation (IVGEN) experiment onboard the International Space Station (ISS), Increment 23/24, during May 2010. This hardware was a demonstration experiment to generate intravenous (IV) fluid from ISS Water Processing Assembly (WPA) potable water using a water purification technique and pharmaceutical mixing system. The IVGEN experiment utilizes a deionizing resin bed to remove contaminants from feedstock water to a purity level that meets the standards of the United States Pharmacopeia (USP), the governing body for pharmaceuticals in the United States. The water was then introduced into an IV bag where the fluid was mixed with USP-grade crystalline salt to produce USP normal saline (NS). Inline conductivity sensors quantified the feedstock water quality, output water purity, and NS mixing uniformity. Six 1.5-L bags of purified water were produced. Two of these bags were mixed with sodium chloride to make 0.9 percent NS solution. These two bags were returned to Earth to test for compliance with USP requirements. On-orbit results indicated that all of the experimental success criteria were met with the exception of the salt concentration. Problems with a large air bubble in the first bag of purified water resulted in a slightly concentrated saline solution of 117 percent of the target value of 0.9 g/L. The second bag had an inadequate amount of salt premeasured into the mixing bag resulting in a slightly deficient salt concentration of 93.8 percent of the target value. The USP permits a range from 95 to 105 percent of the target value. The testing plans for improvements for an operational system are also presented.

Related URLs:

Disruption of an Aligned Dendritic Network by Bubbles During Re-melting in a Microgravity Environment

by on 9 June 2015in Physical Sciences No comment

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.

Related URLs:
http://dx.doi.org/10.1007/s12217-011-9297-y