User:Dr. Olaf Schoele-Schulz/sandbox

Scientific Objectives and Results
The simulation of Geophysical Fluid Flow under Microgravity (GeoFlow) investigated the flow (thermal convection) of a viscous  incompressible fluid in a gap between two concentric spheres, rotating about a  common axis, under the influence of a simulated central force field. This set-up is a model of the Earth´s liquid core but is of importance as well for astrophysical and geophysical problems, like global scale flow in the atmosphere, the oceans, and in the liquid  nucleus of planets.

The sperical model is complex to be simulated while experiments under earth gravity suffer from interactions with the simulated central force field.

Subsequently, the microgravity experiment focussed on


 * The stability of the basic states and its transitions for both the non-rotating and rotating situations
 * The characteristics of the convection flows and in particular their symmetries
 * The critical Rayleigh number which denotes linear stability and marks the onset of thermal convection
 * The stability diagram for the different states and the occurrence of multi-stability
 * The energy transport from the inner sphere to the outer sphere and the characteristic wave numbers
 * Time dependent up to chaotic behavior; drift velocities and non-linear dynamics
 * In GeoFlow I, a liquid with negligible viscosity dependence on temperature has been investigated to determine fundamental fluid-dynamic relations
 * In GeoFlow II, a liquid with high viscosity dependence on temperture was applied to investigate particularly effects relevant for mantle convection

The experiment series deliverd a vast amount of scientific data (> 100GB) and improved the understanding of the hydrodynamic background as well as geophysical effects on the earthe tectonics substantially.

Technical Concept
The experiment consists of a set of two concentric spheres, capable of beeing rotated at common or different rotational speed. The gap between the spheres is filled by the viscous, incompressible experiment liquid.

A central force field (10 kV ac), is applied between the inner and outer sphere. A thermal gradient of up to 10K can be established between both spheres through manipulation of the cooling loops.

The resulting convection pattern of the experiment liquid is optically observed using Wollaston Shearing interferometry, Schlieren and Shadowgraphy.

The experiment set-up together with related control avionics, sensors, motors, high voltage generator and thermal control is installed inside an FSL standard experiment container (400x270x280 mm). This conatiner provides two windows supporting access for the Fluid Science Laboratory optical diagnostics.

GeoFlow was inserted by the ISS crew various times (for history, see below). The experiments have been carried-out fully automatically by the assigned User Support Operation Center (USOC). The science team was involved in the experiment execution and received the resulting data through exclusive connection to the USOC.

Mission History
The GeoFlow experiment was developed as first Fluid Science Laboratory payload under ESA contract by a European industrial consortium lead by Airbus Defence and Space (Astrium at that time). Development activities started 2002. The GeoFlow I mission was performed in the frame of ISS increment 17 in 2008. After return and refurbishment, the experiment was re-launched for GeoFlow II mission on ISS increment 25/26 in 2010. It continued operation until 2016 with subsequent final decommissioning in 2018.

Scientific Objectives and Results
One of the most relevant problems in emulsion technology concerns the control of emulsion stability. For example, high stability and methods of long-term stability prognosis are necessary for emulsions in foods, cosmetics, pharmacy etc. Separation of the two phases and then, destabilisation, is instead required in waste water processing and oil recovery. In both cases, the target can be achieved by introducing specific additives (like surfactants) which adsorb and modify the properties of droplet interfaces. Thus, it is clear that the adsorption of surface active molecules plays a fundamental role in emulsion science.

However, at present, the links between the physical chemistry of the droplets interface to the collective properties of an emulsion are only qualitative, so that the criteria used in industry are mainly empirical. The FASES project has aimed at reducing this gap, which is today an important limitation of the emulsion science and for the development of applications.

Fases (Fundamental and Applied Studies of Emulsion Stability) studies the links between the physical chemistry of the droplets interface, the liquid films and the collective properties of an emulsion. Particular focused are:


 * Characterisation of a liquid/liquid interface Surfactant adsorption dynamics.
 * Characterisation of Drop/drop interactions and the behaviour of the liquid film between the drops.
 * Droplet dynamics and evolution of the droplet size distribution during emulsion destabilisation.
 * Systematic studies on model emulsions will allow developing methods for the evaluation and prediction of systems stability.

The additives (particles and surfactant) added in emulsion can hardly be studied on ground because the gravity modifies the physical properties at two scales: At the microscopic scale, the gravity provokes liquid fluxes and modifies interface thinness. The surfactant transfer effects are then masked. In microgravity, interfaces elasticity is only driven by surfactant concentration; adsorption and diffusion of surfactant could be studied with a great accuracy.

At the macroscopic scale, the drainage (creaming) is an effect faster and/or stronger than the coalescence (film rupture) and aggregation (clustering of droplets). Microgravity conditions avoid the drainage; the surfactant dynamic and particles effects drive then alone the structural evolution. This experiment together with FASTER and another 2 performed in the FAST (Facility for Adsorption and Surface Tension) facility addresses single and multiple interfaces, as affected by various surfactants. An important part of the programme aims at establishing links between emulsion stability and physicochemical characteristics of droplet interfaces. Further experiments are planned to investigate droplet dispersion in emulsions and phase inversion. On the basis of these studies, the team will generate a model of emulsion dynamics to be transferred to industrial applications.

Technical Concept
The Fases experiment container contains 44 cells (3 types: ITEM-S, ITEM-F and EMPI)

The 44 cells are positioned in a carrousel. The position of a cell is not necessarily related to the experimental sequence. However the final arrangement will be defined with respect to the ongoing tests about life time adsorption on the cell wall and leakage.

A run is a full experiment for 1 temperature for ITEM and at 1 time for EMPI.

Scan

The ITEM cells are scanned by a microscope in two ways per scan: one way and return. The scan generates images which allow rebuilding the structure of the emulsion. The amount of data depends of the scanning step (distance between two images) and of the scanning velocity (number of images to be stored per second).

One way scan

In a one-way scan, the microscope advances across the viewing range in only one direction. The amount of data generated is half that of a nominal two-way scan.

ITEM-S

22 samples


 * 1) 1 to #8 are processed 3 times (3 runs per sample) at 3 different temperatures


 * 1) 9 to #22 are processed 1 time

ITEM-F

6 samples experiments are processed 4 times

EMPI experiments

16 samples, processed 1 time (1 run per sample)

The cells more sensitive to aging will be used first. The cells arrangement in the carrousel will be defined with respect to the on-going tests about life time and leakage.