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: Viscosity
Viscous fingering (VF) is an interfacial hydrodynamic instability phenomenon observed when a fluid of lower viscosity displaces a higher viscous one in a porous media. In miscible viscous fingering, the concentration gradient of the undergoing fluids is an important factor, as the viscosity of the fluids are driven by concentration. Diffusion takes place when two miscible fluids are brought in contact with each other. However, if the diffusion rate is slow enough, the concentration gradient of the two fluids remains very large during some time. Such steep concentration gradient, which mimics a surface tension type force, called the effective interfacial tension, appears in various cases such as aqua-organic, polymer-monomer miscible systems, etc. Such interfacial tension effects on miscible VF is modeled using a stress term called Korteweg stress in the Darcy's equation by coupling with the convection-diffusion equation of the concentration. The effect of the Korteweg stresses at the onset of the instability has been analyzed through a linear stability analysis using a self-similar Quasi-steady-state-approximation (SS-QSSA) in which a self-similar diffusive base state profile is considered. The quasi-steady-state analyses available in literature are compared with the present SS-QSSA method and found that the latter captures appropriately the unconditional stability criterion at an earlier diffusive time as well as in long wave approximation. The effects of various governing parameters such as log-mobility ratio, Korteweg parameters, disturbances' wave number, etc., on the onset of the instability are discussed for, (i) the two semi-infinite miscible fluid zones and (ii) VF of the miscible slice cases. The stabilizing property of the Korteweg stresses effect is observed for both of the above mentioned cases. Critical miscible slice lengths are computed to have the onset of the instability for different governing parameters with or without Korteweg stresses. These stabilizing properties of the Korteweg stresses captured in this present study are in agreement with the numerical simulations of fully nonlinear problem and the experimental observations reported in the literature.
The Shear History Extensional Rheology Experiment (SHERE) is an International Space Station (ISS) experiment designed to study the effects of a preshear history on the transient extensional viscosity of a dilute polymer solution in a uniaxial stretching flow. The absence of gravitational body forces allows us to measure the capillary thinning of the fluid filament after cessation of the extensional deformation without sagging of the liquid bridge. Understanding the deformation and thinning of polymeric solutions in complex flows containing both shearing and extensional kinematics is particularly relevant in a wide variety of industries, including fiber-spinning, injection molding, food and consumer product processing, as well as future `containerless processing' operations. The SHERE experiment offers the ability to preshear the test samples before imposing a uniaxial stretching flow in order to explore the impact of this preshearing on the sample extensional viscosity and elastocapillary thinning. After the SHERE main hardware was launched to the ISS on-board Shuttle Mission STS-120, two batches of 20 and 25 fluid samples were successively launched on-board Shuttle Missions STS-123 and STS-126. The SHERE experiments were performed by astronauts Greg Chamitoff and Mike Fincke between July 2008 and January 2009. In this talk, we will focus on the main results obtained for a well-characterized dilute polymer solution and compare them to ground-based experiments. In addition, we will show potential applications of the current microgravity experimental findings.
Modeling of the Fluid Merging Viscosity Measurement (FMVM) International Space Station experiment with COMSOL MultiPhysics
The purpose of FMVM was to measure the rate of coalescence of two highly viscous liquid drops and correlate the results with the liquid viscosity and surface tension. The experiment takes advantage of the low gravitational force free floating conditions in space allowing the unconstrained coalescence of two nearly spherical drops. The merging of the drops is accomplished by deploying them from a syringe and suspension on Nomex threads. An astronaut’s slow manipulation of one of the drops toward a stationary droplet till there is contact initiates the droplet coalescence. Coalescence and merging occurs due to shape relaxation and reduction of surface energy, being resisted by the viscous drag within the liquid. Experiments were conducted onboard the International Space Station in July of 2004 and subsequently in May of 2005. The coalescence was recorded on video and down-linked near real-time. When the coefficient of surface tension for the liquid is known, the increase in contact radius can be used to determine the coefficient of viscosity for that liquid. The viscosity is determined by fitting the time to achieve contact neck diameter equal to half of the initial droplet diameter. This time is compared with a relaxation time scaling coefficient to arrive at the liquid viscosity. Recent fluid dynamical numerical simulations with COMSOL MultiPhysics of the coalescence process will be presented. The results are important for a better understanding of the coalescence process. The experiment is also relevant to liquid phase sintering, free form in-situ fabrication, and as a potential new method for measuring the viscosity of viscous glass formers at low shear rates.
From isoviscous convective experiment ‘GeoFlow I’ to temperature-dependent viscosity in ‘GeoFlow II’—Fluid physics experiments on-board ISS for the capture of convection phenomena in Earth's outer core and mantle
With the hydrodynamic experiment ‘GeoFlow’ (Geophysical Flow Simulation) instability and transition of convection between two spherical shells are traced. The flow is driven by a central-symmetry buoyancy force field in microgravity conditions. We performed experiments for a wide range of rotation regimes, within the limits between non- and rapid-rotation. Here we focus on the non-rotational convection in an isoviscous experimental fluid as in ‘GeoFlow I’ and the preparation of ‘GeoFlow II’, that uses a temperature-dependent viscous fluid. Theoretical predictions on thermal, dielectric and optical performance of the fluid suggest the use of an alkanole, i.e. 1-Nonanol as working fluid for ‘GeoFlow II’. Initial ground based experiments demonstrate the influence of the viscosity contrast on fluid flow patterns. Specific results from the ‘GeoFlow I’ experiment, i.e. steady-state convection above a threshold and transition to chaos, are used as a reference.
During the Space Shuttle “down period” a call was put out for low upmass payloads. One of these “low up mass” International Space Station science experiments is the “Fluid merging Viscosity Measurement”, FMVM investigation. The purpose of FMVM is to measure the rate of coalescence of two highly viscous liquid drops and correlate the results with the liquid viscosity and surface tension. The experiment take advantage of the low gravitational free floating conditions in space to permit the unconstrained coalescence of two nearly spherical drops. The merging of the drops is accomplished by deploying them from a syringe and suspending them on 2 Nomex threads followed by the astronaut’s manipulation of one of the drops towards a stationary droplet till contact is achieved. Coalescence and merging occurs due to shape relaxation and reduction of surface energy, being resisted by the viscous drag within the liquid. The coalescence was recorded on video (ISS VTR) and some of the data was downlinked near real-time. A range of drop diameters, different liquids with differing viscosity and surface tensions should yield a large range of experiment parameters used to correlate with theory and to compare with numerical experiments. The results are important for a better understanding of the coalescence process. The experiment is also relevant to liquid phase sintering and is a potential new method for measuring viscosity of viscous glass formers at low shear rates.
The concept of using low gravity experimental data together with fluid dynamical numerical simulations for measuring the viscosity of highly viscous liquids was recently validated on the International Space Station (ISS). After testing the proof of concept for this method with parabolic flight experiments, an ISS experiment was proposed and later conducted onboard the ISS in July, 2004 and subsequently in May of 2005. In that experiment a series of two liquid drops were brought manually together until they touched and then were allowed to merge under the action of capillary forces alone. The merging process was recorded visually in order to measure the contact radius speed as the merging proceeded. Several liquids were tested and for each liquid several drop diameters were used. It has been shown that when the coefficient of surface tension for the liquid is known, the contact radius speed can then determine the coefficient of viscosity for that liquid. The viscosity is determined by fitting the experimental speed to theoretically calculated contact radius speed for the same experimental parameters. Experimental and numerical results will be presented in which the viscosity of different highly viscous liquids were determined, to a high degree of accuracy, using this technique.
Multipotent neural precursors can be cultured in suspension bioreactors as aggregates of stem cells and progenitor cells. However, it is important to limit the size of the aggregates, as necrotic centers may develop at very large diameters. Previously, we have shown that the hydrodynamics within a suspension bioreactor can be used to control the diameter of NSC aggregates (D-MAVO < 150 μm) below sizes where necrosis would be expected to occur. In the present study, power law correlations were developed for our bioreactors showing the dependence of the maximum mean aggregate diameter on both the kinematic viscosity of the medium and the power input per unit mass of medium, The power input was manipulated by changing the agitation rate (60-100 rpm), and the viscosity was manipulated through the addition of non-toxic levels of carboxymethylcellulose. The study also confirmed that the maximum liquid shear generated at the surface of the aggregates was sufficient to dislodge single cells, thus limiting the maximum diameter of the aggregates, without causing cell damage (τ(max) = 9.76 dyn/cm(2)). This is a first step in the development of a reproducible, scaled-up process for the production of neural stem cells for therapeutic applications including the treatment of neurodegenerative disorders and acute central nervous system injuries. (C) 2002 Elsevier Science B.V. All rights reserved.
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Measurements are reported of the evolution of bioconvective patterns in shallow, dense cultures of microorganisms subjected to varying gravity. Various statistical properties of this random, quasi-two-dimensional structure have been found: Aboav's law is obeyed, the average vertex angles follow predictions for regular polygons, and the area of a pattern varies linearly with its number of sides. As gravity varies between 1 g and 1.8g (g = 9.8 m s-1), these statistical properties continue to hold despite a tripling of the number of polygons and a reduced average polygon dimension by a third. This work compares with experiments on soap foams, Langmuir monolayer foams, metal grains, and simulations.