Effects of standing sound wave on droplet combustionMorita, T.; Aoki, K.; Satoh, K.; Fujimori, T.; Tanabe, M.
doi: 10.1007/bf02870313pmid: N/A
Combustion of an isolated fuel droplet in acoustic fields is investigated by microgravity experiments. The influence of standing sound wave is examined by varying amplitude of velocity fluctuation, frequency of sound and location of droplet. Variation of flame shape and burning rate is determined. As a result, spreading flame to one direction as well as normal gravity is observed as amplitude of velocity fluctuation increases. On the other hand, hemispheric and conical flames are observed when the amplitude of velocity fluctuation is small. Direction of flame spread is changed depending on relative location between velocity anti-node and the droplet. The cause is considered as acoustic radiation force in standing sound wave. Burning rate is significantly enhanced by velocity fluctuation and the amount of the enhancement is changed by sound frequency or relative location.
The study of weak oscillatory flows in space experimentsShevtsova, Valentina M.; Melnikov, D. E.; Legros, J. C.
doi: 10.1007/bf02870314pmid: N/A
The effects of residual accelerations have been studied by using three-dimensional modeling of the flow in a rectangular cell filled with a liquid, Pr=20, the walls of which were kept at different temperatures. The system was subjected to an acceleration field, which can be decomposed into two parts: a steady component and another one which varies slowly with time, the frequency is about f0≈10−3 Hz. The convective heat transport and flow characteristics are discussed for different parameters of g-jitter. The high and low frequency modulation of a sinusoidal g-jitter is discussed. To capture many of the essential characteristics of buoyancy-induced convection a new approach is suggested, which was developed based on the observation of the trajectories of tracer particles. On the one hand, it is a typical way to record the flow in experiments. On the other hand, creating database of different types of trajectories gives the possibility to solve the inverse problem. The shape of the trajectory depends on the g-jitter parameters. It is shown that for slow convective motions the tracer particles perform loops along trajectory due to g-jitter with low frequencies, and the additional high frequencies only cause trembling of the shape of these loops. Taking the experimentally recorded trajectories of tracer particles and comparing with those in the database, one can draw a conclusion about the amplitude and direction of the resulting gravity vector during the experiment.
Effect of convective disturbances induced by g-jitter on the periodic precipitation of lysozymeLappa, Marcello; Carotenuto, L.
doi: 10.1007/bf02870315pmid: 14577450
Numerical simulations are carried out to investigate the crystallization process of a protein macromolecular substance under two different conditions: pure diffusive regime and microgravity conditions present on space laboratories. The configuration under investigation consists of a protein reactor and a salt chamber separated by an “interface”. The interface is strictly related to the presence of agarose gel in one of the two chambers. Sedimentation and convection under normal gravity conditions are prevented by the use of gel in the protein chamber (pure diffusive regime). Under microgravity conditions periodic time-dependent accelerations (g-jitter) are taken into account. Novel mathematical models are introduced to simulate the complex phenomena related to protein nucleation and further precipitation (or resolution) according to the concentration distribution and in particular to simulate the motion of the crystals due to g-jitter in the microgravity environment. The numerical results show that gellified lysozyme (crystals “locked” on the matrix of agarose gel) precipitates to produce “spaced deposits”. The crystal formation results modulated in time and in space (Liesegang patterns), due to the non-linear interplay among transport, crystal nucleation and growth. The propagation of the nucleation front is characterized by a wavelike behaviour. In microgravity conditions (without gel), g-jitter effects act modifying the phenomena with respect to the on ground gellified configuration. The role played by the direction of the applied sinusoidal acceleration with respect to the imposed concentration gradient (parallel or perpendicular) is investigated. It has a strong influence on the dynamic behaviour of the depletion zones and on the spatial distribution of the crystals. Accordingly the possibility to obtain better crystals for diffraction analyses is discussed.