Vibration influence on morphological instability of a solidification frontLyubimov, Dmitry; Lyubimova, Tatyana; Tcherepanov, Anatoly; Roux, Bernard; Billia, Bernard; Nguyen-Thi, Henri
doi: 10.1007/BF02945993pmid: N/A
The paper deals with the vibration influence on the stability of a planar solidification front moving with constant average velocity. The case of high frequency vibrations with small amplitude is studied. The density dependence on the solute concentration is accounted for in the framework of the Boussinesq approach. The equations for average velocity and concentration fields are obtained by multiple scale and averaging methods. A number of limit cases are studied analytically, by perturbation methods. For finite values of governing parameters the threshold of morphological instability is determined numerically. It is found that the vibrations normal to the solidification front exert destabilizing effect whereas tangential vibrations suppress the development of morphological instability.
Thermocapillary effects on low-g Pool Boiling from microheater arrays of various aspect ratioHenry, Christopher; Kim, Jungho
doi: 10.1007/BF02945970pmid: N/A
Pool boiling heat transfer measurements from heaters of varying aspect ratio were obtained in low-g (0.01 g ± 0.025 g) and high-g (1.7 g ± 0.5 g) using the KC-135 aircraft. The heater aspect ratio was varied by selectively powering 2×2, 2×4, 2×6, 2×8, and 2×10 arrays of heaters in a 10×10 heater array containing individual heaters 700×700 μm2 in size. Control circuitry was used to maintain a nominally isothermal boundary condition on the heater surface while the power dissipated by the heater was measured. Steady-state boiling data in low-g and high-g were obtained using FC-72 as the working fluid at two bulk fluid temperatures. At high wall superheats, boiling performance appears to decrease with an increase in aspect ratio. Strong thermocapillary convection was observed for a negligible gas concentration in the liquid. CHF was not observed for the heater used in this study indicating that CHF in low-g may be highly dependent on the surface characteristics of the heater in addition to the heater size.
Optical properties of silicon micro and nanocrystalsBoisjoli, A.; Leclerc, J.; Piché, M.; Slobodrian, R.; Rioux, C.; Raymond, S.
doi: 10.1007/BF02945940pmid: N/A
Silicon nanocrystal aggregates have been produced in an inert argon gas by a pulsed laser vaporization-condensation technique using the second harmonic of a Nd: YAG laser. In our previous work, it has been shown that materials generated by evaporation-condensation technique present a variety of structures depending on the conditions of production. A theoretical model has been elaborated from a multitude of metallic samples, taking into consideration the effect of the main physical factors on the resulting morphology. This model has been applied to silicon in order to produce silicon nanocrystals with specific structural characteristics. We carried out an investigation of the influence of the structure on the optical properties of silicon nanocrystals. In this report, we present the first results from this investigation. We have explored the inert gas pressure variation effect on the resulting nanocrystallite structures. Investigation under scanning electron microscopy (SEM) has revealed a weblike arrangement whose density gradually increases with the value of pressure. The deposits have been exposed to ambient air for eight months before photoluminescence (PL) measurements. The oxidized nanocrystals exhibited PL and the broad bands seem composed of multiple narrower bands. Silicon nanocrystals are the best candidates for the understanding of the extended red emission (ERE) visible in spectroscopic observations of many astronomical objects.
Experimental investigation of Marangoni convection and vibration-induced crystal motion during protein crystal growthGamache, Olivia; Nakamura, Hirohiko; Kawaji, Masahiro
doi: 10.1007/BF02946002pmid: N/A
The occurrence of Marangoni convection during cytochrome c’ crystal growth and vibration-induced motion of lysozyme crystals were investigated using a High Density Protein Crystal Growth (HDPCG) apparatus. Particle image velocimetry was used to visualize fluid motion, but no particle motion was observed, which suggests that under the experimental conditions used, Marangoni convection is not a significant cause of fluid and crystal motion. When horizontal vibrations of controlled amplitude and frequency were applied to the HDPCG apparatus, lysozyme crystals located on the liquid-vapour interface of the HDPCG cell made significant movements up to 0.5mm in amplitude and velocities reaching 0.06mm/s. These results from the Marangoni convection and horizontal vibration experiments suggest that protein crystal movements observed in past space experiments were most likely caused by g-jitter on the spacecraft rather than Marangoni convection.
Determination of butanol distribution on salol-butanol crystals using Micro Raman SpectroscopyShimaoka, Taro; Kagi, Hiroyuki; Natsuisaka, Makoto; Adachi, Satoshi; Inatomi, Yuko
doi: 10.1007/BF02945957pmid: N/A
We carried out several analytical studies in order to determine the butanol distribution on a salol-butanol crystal. This work is required for a research using microgravity condition focused upon the in-situ observation with an interferometer of the temperature and concentration field for the organic transparent crystal (salol-butanol). In order to evaluate the concentration field for the liquid phase with an interferometer in case of crystal growth from solution in space, it is significant to determine the distribution of solute (butanol) on starting crystal before sample launching using a non-destructive analytical method. The Micro Raman Spectroscopy (MRS) was choice as the most appropriate analytical method among several analytical methods. We prepared a salol-butanol crystal enclosed into the 1mm thick quartz glass ampoule in order to verify the propriety for MRS. Obtained Raman spectrums for salol, butanol and salolbutanol crystal show that the butanol 2D-distribution on salolbutanol crystal can be determined by MRS. These results also demonstrate that there are no influences of thick glass cell upon measurements and that 3D-measurement is possible. In conclusion, we argue that MRS is the most appropriate method for determination of the 2D- and/or 3D- distribution of solute on the crystal among several non-destructive analytical methods.
Numerical and experimental investigation of solid particle motion in a fluid cell under microgravitySimic-Stefani, Sonja; Hu, Howard; Kawaji, Masahiro
doi: 10.1007/BF02945995pmid: N/A
This research aims at understanding the mechanisms and parameters that affect particle motion induced by g-jitter. Simultaneous experimental (parabolic flights) and numerical work was conducted to study the motion of a spherical particle in a microgravity environment subjected to vibrations in either horizontal or vertical direction. The data from both vertically and horizontally vibrated experiments clearly show that the investigated particle properties, size and density, affect the amplitude of the particle motion. In all experiments the amplitude of the particle motion increased with the density and diameter of the particle in the cell frame of reference. It was also observed that the particles moved at the frequency equal to that of applied vibration. These results are consistent with the preliminary numerical simulation predictions. Numerical simulations also showed that increasing the viscosity of the surrounding fluid would reduce the amplitude of the particle motion.
Surface tension, phase separation and solidification of undercooled Cu-CoEgry, I.; Herlach, D.; Kolbe, M.; Ratke, L.; Reutzel, S.; Perrin, C.; Chatain, D.
doi: 10.1007/BF02945945pmid: N/A
The system Cu-Co has a metastable miscibility gap in the under-cooled liquid phase which can be accessed by electromagnetic lévitation. Unsupported two-phase liquid drops display a variety of physical phenomena, including wetting, phase separation and solidification, which can be studied on this model system. This paper reports theoretical and experimental results which have been obtained within the CuCool project, funded by ESA, DLR and CNES through the MAP programme.