DYNAMICS / DIFFUSION & GROWTH
THE MEASUREMENT OF THE QUASI STEADY ACCELERATION
ON BOARD THE ISS
G. Poletti
University of Milan,via Trentacoste 2, I-20134 Milan ,Italy
It is now ascertained that for most of the experiments of material processing
and fluid science the quality of the experimental conditions is mainly determined
by the low frequency microgravity value. These experiments can tolerate much
greater acceleration disturbances if they are short lasting or at high frequency.
This is clearly reflected in the acceleration masks as a function of frequency
that are assumed as acceptable on board of the ISS. Therefore the measurement
of the residual quasi steady g-vector, which is essentially the sum of the accelerations
due to the aerodynamic drag and the gravity gradient, comes out to be the most
important. Furthermore it has been argued that in fluid physics experiments
aligning the cell in the residual g-vector direction can reduce the effects
of the microgravity on the experiment. This could be an alternative to the use
of the Isolation Mounts for a given class of experiments; but the measurement
of the modulus of the residual quasi steady microgravity is very difficult with
the low frequency accelerometers generally used and in particular the measurement
of the direction of the g-vector has never been tried.
A new conception accelerometer is presented that overcomes some of the problems
of the simple mass-spring units that have been commonly used as the basis for
most accelerometer systems. The basic idea is to measure the law of motion of
a small sphere free- floating in a vacuum cell integral with the ISS. The optical
devices recording the position of the sphere as a function of time are integral
with the cell and therefore suffer the same accelerations of the ISS while the
small sphere is by definition in free fall. From the recorded data, the magnitude
and the direction of the quasi steady g-vector are easily calculated with good
accuracy. Sensitivities better than 0.1 micro-g can easily be achieved. In addition
the system does not react to relatively high (above 0.5 Hz approximately) frequency
g-jitter making easier the interpretation of the experimental data.
The device will be located inside the GLAD facility that will be taken on board
the ISS by the UF#3 flight of NASA. The envisaged overall configuration of the
facility is illustrated.
The expected performances of the device are discussed on the basis of the results
of numerical computer simulations of the experiment based on the DAC 7 (Dynamic
Analysis Cycles) calculations concerning the US Lab performed by Boeing. The
simulations show in addition that in the above position the direction of the
residual g-vector remains constant within several degrees during the orbit.
MEASUREMENT OF INERTIAL PROPERTIES OF FREE-FLOATING BODIES ON ISS
J. P.B. Vreeburg
National Aerospace Laboratory, Space Department, PB 90502, NL-1006 BM Amsterdam,
The Netherlands
A body is characterized by ten inertial properties, namely mass (1), center
of mass location (3) and inertia tensor (6). The mass property, or weight on
earth, is a useful measurement data with many applications. The remaining properties
depend on the mass distribution, including shape, and measurement data can be
used to diagnose such distribution. A relevant application would be the determination
of liquid shift in an astronaut. A necessary condition is to take the data in
a reference posture in order to determine the difference measurement.
Instruments to measure mass and scales are available in great variety. For the
other inertial properties, only few designs exist and the market is small. Space
vehicles customarily have the center of mass and inertia tensor determined because
these properties are necessary input for attitude control systems. Need for
data exists also in the biodynamics field.
Knowledge of the motion of a free-floating body can be processed in order to
determine its inertial properties. The appropriate equations will be discussed,
and various options for the construction of a viable instrument will be assessed.
Applicable sensors are accelerometers and gyroscopes. Results of simulations
will be given to illustrate the achievable accuracies.
MASS-DIFFUSION BUBBLE GROWTH IN REDUCED GRAVITY
M. C. Sneep1, R. de Bruijn1, H. Th. Lotz1,
A. C. Michels1, C. Panoutsos2, T.
D. Karapantsios2,3, V. Bontozoglou2, M Kostoglou4
1: Van der Waals-Zeeman Instituut, Universiteit van Amsterdam, Valckenierstraat
65, 1018 XE Amsterdam, The Netherlands. 2: Dept. of Mechanical Engineering,
University of Thessaly, Pedion Areos, 38 334 Volos, Greece. 3: Dept. of Chemistry,
University of Thessaloniki, Univ. Box 116, 540 06 Thessaloniki, Greece. 4: Chemical
Process Engineering Research Institute, P.O. Box 1517, 540 06 University city,
Thessaloniki, Greece.
This work investigates the growth of bubbles emerging from a liquid saturated
with CO2 when its temperature is suddenly raised above the saturation
value. Experiments were performed under low gravity conditions during ESA’s
25th and 26th Parabolic Flight Campaigns. From an experimental
viewpoint, gravity poses a plausible restriction not only due to natural convection
effects but also due to bubble deviation from the spherical shape, which is
particularly true for low surface tension fluids.
Three test fluids were studied -water, 20/80 w/w water/glycerol mixtures and
n-heptane- in order to examine the role of viscosity and surface tension on
bubble growth dynamics. Two types of heaters were used. A small spherical one
to study the growth of individual bubbles at the tip of the heater and a larger
flat one to study the competition among neighboring bubbles growing simultaneously
over the heater. Only results from the former one are presented here.
Heat pulses of variable power and duration were employed. For all test fluids,
bubble expansion was fast at the beginning and slowed down drastically later.
Yet, the bubbles created in n-heptane were considerably larger than in water,
which, in turn, were larger than those formed in water/glycerol mixtures. This,
apparently, shows that the rate of bubble growth depends strongly on the physical
properties of the test fluid.
A mathematical model is formulated which clearly demonstrates the various physical
properties and experimental parameters that can have a significant contribution
on the response of the bubble. The mathematical model is exceedingly complicated
to evaluate for a time dependent heat input to the system since it includes,
among others, transient diffusion-convection equations and moving boundaries.
At this stage, the simplified problem of a bubble growing under constant temperature
was solved in order to gain some physical insight. The advantage of examining
this case is that it affords a self-similarity solution.
SYNTHESIS OF InSb SEMICONDUCTOR CRYSTAL IN SHORT-DURATION MICROGRAVITY
T. Okutani, H. Minagawa, H. Nagai, Y. Nakata, M. Sasamori and K. Kamada1
Microgravity Materials Laboratory, National Institute of Advanced Industrial
Science and Technology, 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo 062-8517,
Japan, 1 Japan Space Utilization Promotion Center, 3-30-16 Nishiwaseda,
Shinjuku-ku, Tokyo 169-8624, Japan
The advantages of working in a microgravity (µg) environment are the lack of
gas or liquid mass transfer by convection, the clearly apparent surface tension
of liquids, and the homogeneous mixing of substances with different specific
gravity. It is impossible to obtain such a unique environment on the ground.
To synthesize high-quality crystalline materials such as semiconductors using
a µg environment, many experiments have been conducted in space where long µg
periods can be obtained. Most of the space experiments were concerned with crystal
growth by Chochralski, Bridgman and other methods. Up to now, it has been considered
impossible to synthesize high-quality crystalline materials using the short-duration
µg environment obtained by drop towers, drop shafts, and drop tubes.
When solidifying materials using containerless processing or very slow cooling
conditions, nucleation can be suppressed and the molten metal and alloy can
be cooled below the melting point. This phenomenon is called supercooling. When
the molten metals and alloys are cooled in µg, supercooling is presumed to be
observed during solidification because a homogeneous melt is produced in the
absence of convection. This assumption is supported by the fact that supercooling
was observed in the cooling of InSb melt under µg, but not under 1g, even in
solidification using contact processing.
Almost all binary compound semiconductors such as InSb and GaAs are formed by
the solidification from melts directly, so-called line-compounds. These high-quality
crystalline semiconductors are assumed to be synthesized by well-controlled
solidification such as unidirectional solidification in µg, because of homogeneous
melts. A short-duration µg environment obtained using a drop tower can be used
to synthesize high-quality crystalline semiconductors, because the homogeneous
melts can be obtained by even rapid cooling using coolant.
Uni-directional solidification experiments of InSb melts by use of liquid nitrogen
and chill block as a coolant were conducted in a µg environment of 10-3g
for 1.2 seconds. The µg environments were obtained using the HNIRI's 10m free-fall
drop tower.
Supercooling was observed in all µg experiments and the results showed the InSb
melt in µg was homogeneous. The cooling rates were 262 K/sec and 170 K/sec in
case of liquid nitrogen coolant and chill block, respectively. InSb synthesized
in µg was high quality single crystal.
IGC-PROCESS-CHARACTERIZATION IN A µG-ENVIRONMENT
M. Meier, R. Ristau, C. Egbers
Brandenburg University of Technology, Karl-Liebeknecht-Strasse 102, D-03046
Cottbus, Germany
High porous metal nanopowders are useful filler materials in conductive polymer-matrix
composites, because they combine electrical conductivity with improved thermo-mechanical
properties of the composite. These ultra-pure powders, which are produced by
a specially designed Inert Gas Condensation (IGC) process, develop from coalescence
growth and coagulation processes of metal vapor in a helium gas as a result
of succeeding nucleation. The agglomeration of metallic nanoparticles in such
an aerosol has been monitored on-line as a function of background pressure and
particle content in the aerosol. Laser Doppler Velocimetry (LDV) and Particle
Image Velocimetry (PIV) have been used to prove quantitative measurement of
the particle velocity. The results are correlated with the data, which has been
obtained from microscopical observation by a new particle analysing system.
First microgravity experiments with the IGC-facility will be done in a parabolic
flight campaign.
THE FASES PROJECT: THE STUDY OF ADSORPTION
DYNAMICS AND EMULSION STABILITY ON THE ISS
L. Liggieri, M. Ferrari1, F. Ravera1, G. Loglio2, R. Miller3, D. Clausse4,
A. Steinchen5, J.D. Sylvain6, A. Passerone1
1) ICFAM - CNR, via De Marini 6, 16149 Genova - Italy. 2) Dip. Organic Chem.-
Univ. Firenze, Italy. 3)Max-Planck Inst. For Colloids and Interfaces, Golm -
Germany.4) Univ. de Téchnologie Compiègne , France. 5) Univ. Aix-Marseille
III, Marseille - France. 6) Univ. Nice, France
FASES (Fundamental and Applied Studies in Emulsion Stability) is one of the
projects selected by ESA in the framework of Microgravity Application Programme
(MAP) for the ISS.
The project, proposed by a European network of laboratories chaired by ICFAM,
is aimed at investigating the emulsion stability in relation to the physical-chemistry
of droplet interfaces. In fact, the main mechanisms involved in emulsion destabilisation
are the droplet aggregation and coalescence. Both are strongly influenced
by the basic properties of the liquid-liquid interfaces, like the adsorption
dynamics of surfactants and the dynamic elasticity of interfaces and films.
The results of the project are important both for science and technology and
will allow the models of the droplet dynamics inside an emulsion to be input
with a rigorous description of the interface and film physical-chemistry.
Microgravity has a great relevance for these studies, in fact it provides suppression
of the droplet segregation and offers a purely diffusive environment, which
are effective conditions for the study of the adsorption dynamics and the droplet
coalescence and aggregation. Thus, to provide relevant data and to test the
developed models, key microgravity experiments are planned, in the framework
of the project. To this aim, two facilities have been planned for the ISS, respectively
for studying the physical chemistry of single interfaces and the dynamics of
emulsions. These are an upgraded version of FAST (Facility for Adsorption and
Surface Tension studies) housed in the EDR and the devices ITEM and EMPI, housed
in a Fluid Science Laboratory experiment container. FAST is a SpaceHab module,
developed for ESA by Officine Galileo (Italy), to study the properties of adsorbed
layers, already utilised during the STS-95 NASA Shuttle mission and is being
refurbished for a campaign on STS-107 in 2002. The version for the ISS, largely
improved, will be used to study dilational properties of liquid interfaces and
films, the adsorption dynamics and the transfer of surfactant across the interface.
Emulsion dynamics and drop-drop interaction will be investigated by two devices:
ITEM for transparent emulsions, based on optical diagnostics, and EMPI for concentrated
and opaque emulsions (EMPI), based on a advanced calorimetric diagnostics exploiting
the under-cooling properties of microscopic liquid droplets.
In this lecture, the scientific rationale of the project will be given, together
with the description of the planned facilities and microgravity experiments.
The first results of the project will also be given.
PHASE TRANSITION IN HYBRID UNDER VIBRATIONS
D. Beysens1, D. Chatain1, P. Evesque2, Y. Garrabos3
1 ESEME, Service des basses Température, Département de Recherche
Fondamentale sur la Matière Condensée, Commissariat à l’Energie
Atomique, 2 MSSMat, Ecole Centrale de Paris, 92295 Chatenay-Malabry Cedex 20,
France. 3 ESEME, Institut de Chimie de la Matière Condensée de
Bordeaux, 87, avenue du Docteur A. Schweitzer, 33608 Pessac Cedex, France
We investigate the liquid-vapor phase separation of hydrogen near its critical point (33K) when submitted to high frequency vibrations (amplitude 0.3 - 0.5 mm, frequency f = w/2p = 20 - 50 s-1). Gravity effects are compensated in a high magnetic field gradient as provided near the end of a 10 T superconducting coil. The experiments are performed in the range Tc-T » [0.4 – 4 mK], at critical density where the phase separating pattern is interconnected with a pseudo-wavelength Lm. We explain the experimental findings by the presence of inertial velocity gradients ∆V between the vapor and liquid domains. These gradients are significant only when Lm becomes larger than the viscous boundary layer d » (w/v)1/2. The gradients produce local shear flows whose time average is non-zero and which accelerate the growth of the domains.
