Microgravity Science and Technology最新文献

Surface tension and viscosity of complex Ti-based industrial alloys are important for simulation of liquid assisted industrial processes such as casting, joining, crystal growth and infiltration. Modelling of the interface and mass transport during liquid-solid phase transition requires reliable surface tension and viscosity data. Therefore, to obtain accurate predictions of microstructural evolution during solidification related processes, only reliable input data are necessary. In the case of liquid Ti-Al alloys, the experimental difficulties related to high temperature measurements and reactivity of these alloys with supporting materials or containers as well as inevitable presence of oxygen may lead to data gaps including a complete lack of property data. An alternative for container-based methods are containerless processing techniques that offer a significant accuracy improvement and / or make possible to measure temperature and composition dependent thermophysical properties of metallic melts, as in the case of the Ti-Al-Cr-Nb system. Advanced mathematical models and computer simulations, developed in several theoretical frameworks, can be used to compensate the missing data; on the other side, for the validation of theoretical models, the experimental data are used. In the present work, an evaluation of the surface tension and viscosity of liquid Ti-Al-Cr-Nb alloys by means of the predictive models and a comparison to the available experimental data were done. The proposed methodology is a tool to assess the reliability of thermophysical properties data of multicomponent alloy systems.

Some serious errors exist in the above paper. Many concentration profiles are truncated and wrong. The local similarity method used is not correct. The dimensionless Hartmann number is dimensional and wrong.

Simulated microgravity (SMG) is an environmental condition that affects bone density in vertebrates. Ground-based studies typically use a random positioning machine in either a 2D or a 3D mode to assess the effects of SMG, however the meaning of these results is difficult to compare between studies due to different experimental parameters. Here, we exposed larval Danio rerio at 3dpf to 23 h of SMG using a 2D and a 3D mode of rotation, using the same experimental setup. Zebrafish larvae were anaesthetized during the experiment. Our results showed that anesthesia (MS222) did not affect the amount of ossification while SMG-2D treatment slightly reduced the amount of ossification compared with the controls. On the other hand, SMG-3D treatment significantly reduced the overall ossification level of the skeleton. Specifically, the anterior end of the notochord, the ceratobranchial-5, the lower jaw articulation, the pharyngeal teeth, and the operculum were affected compared with control treatments. Overall, these results indicate that SMG-3D produced a more effective SMG effect compared with the SMG-2D. This research provides valuable insight into how different external stimuli such as SMG can cause negative effects on ossification in the developing skeleton in zebrafish.

This paper presents a method to analyse multirotor unmanned aerial vehicles (MUAVs) as microgravity platforms. MUAVs can maintain a free-fall state and provide microgravity owing to their precise thrust control abilities. Moreover, MUAVs are affordable platforms that can be procured at low-cost. Although several MUAVs of various sizes and configurations exist, their capabilities as microgravity platforms are not readily available. Towards this, a framework is developed to estimate microgravity performance measures such as 0g-time, payload capacity, and 0g-quality for a given MUAV. The proposed estimation framework requires only the data provided by the MUAV manufacturer to compute all the microgravity performance measures. The performance as a microgravity platform of several existing MUAVs of various configurations, masses, sizes, and thrust capabilities is estimated by employing this framework. This analysis reveals that there exist MUAVs that can provide microgravity (of the order of (10^{-2}g)) for more than 4 s 0g-time while carrying more than 1 kg payloads. On the other hand, it is also shown that some MUAVs can carry payloads heavier than 90 kgs and provide microgravity for 2 s, which is comparable to the capability of some of the drop tower facilities.

Thermocapillary convection of nanofluid with evaporating phase change interface occurs in a variety of industrial processes such as micro/nano fabrication, ink-jet printing, thin film coatings, etc. Previous studies have mostly focused on the phenomena of thermocapillary convection in pure fluids without phase change. This paper reports the first fundamental experimental work on the thermocapillary flow of a thin nanofluid layer under the effect of evaporation. This research focuses on the behavior of a volatile thin nanofluid layer in a rectangular test cell under the effects of horizontal temperature gradient. The buoyancy effect can be neglected inside this thin liquid layer as in microgravity conditions. HEE7200 and HFE7200-Al₂O₃ nanofluid are used as working fluids to analyze the effect of nanoparticle addition. The results indicate that the linear relationship between the thickness of the liquid layer and the duration of evaporation is not changed by nanoparticles. HFE7200-Al₂O₃ nanofluid always has a higher evaporation rate than its base fluid with the temperature ranging from 2.98 °C to 13.92 °C. The critical Marangoni number for the nanofluid is lower than that of the pure fluid, which indicates that the addition of nanoparticles promotes the flow pattern transition.

In_xGa_1−xSb single crystals have been grown by using a GaSb/InSb/GaSb-sandwich system onboard at the International Space Station (ISS) via vertical gradient freezing method (VGF). In order to investigate the effects of InSb geometry on the InGaSb crystal growth under microgravity and further optimize the future space experiment, two-dimensional axisymmetric numerical simulations were carried out with different thicknesses and diameters of the InSb crystals. Simulation results showed that enough solutes from feed through diffusion is necessary for the crystal growth process and the InSb thickness will affect the axial Ga concentration gradient and therefore affect the crystal growth rates under microgravity. In addition, results also showed that a larger diameter for the InSb crystal will increase the volume crystal growth rates with a flatter shape for the grown crystal interfaces. In summary, simulation suggests a 2 mm or 3 mm thickness and a 12 mm diameter as the geometry of InSb for future space experiments.

We report on the design and the construction of a sounding rocket payload capable of performing atom interferometry with Bose-Einstein condensates of (^{41})K and (^{87})Rb. The apparatus is designed to be launched in two consecutive missions with a VSB-30 sounding rocket and is qualified to withstand the expected vibrational loads of 1.8 g root-mean-square in a frequency range between 20–2000 Hz and the expected static loads during ascent and re-entry of 25 g. We present a modular design of the scientific payload comprising a physics package, a laser system, an electronics system and a battery module. A dedicated on-board software provides a largely automated process of predefined experiments. To operate the payload safely in laboratory and flight mode, a thermal control system and ground support equipment has been implemented and will be presented. The payload presented here represents a cornerstone for future applications of matter wave interferometry with ultracold atoms on satellites.

In droplet actuation, Lamb waves are utilized to manipulate and control liquid droplets on solid surfaces. This paper presents an analytical model for driving droplets using Lamb waves (a type of surface acoustic wave) on a non-piezoelectric substrate. The driving of droplets is simulated using the level set two-phase flow method, and the obtained data are validated through corresponding experiments. The simulation and experimental data are therefore combined to calculate and verify the attenuation of Lamb waves in droplet actuation. The research findings indicate that the droplets absorb the maximum amount of Lamb wave energy when their volume is 50 µL, and at this point, the Lamb wave experiences the fastest attenuation.

A key aspect of space application technology is the generation and control of multi–phase flows. The efficiency of mass and heat transfer can be significantly improved by adding bubbles or droplets into continuous phases. The effects of the ratio of amplitude to bubble diameter (A/D), Bond number (Bo), and different gravity levels (G/g) on bubble centroid motion and shape oscillation are fully analyzed using the VOF method to understand the bubble–centroid trajectory and shape–oscillation mechanism under low–frequency vibrations. The present studies show that A/D, Bo, and G/g have important effects on bubble trajectory and shape oscillation. There are two types of oscillations for bubble shape: regular oscillation and chaotic oscillation. As Bo and A/D increase, bubble oscillation in a gravity–free environment changes from regular to chaotic oscillation. For the present results, bubble oscillations at different gravity levels (except zero–gravity level) are chaotic oscillations. Three types are recognized for the bubble–centroid motion: levitation, rising and sinking. When both A/D and Bo are tiny, a bubble is hung in its initial position in a gravity–free environment. Bubble–centroid motion changes from sinking to rising with an increase in A/D and Bo. The higher the gravity level is, the shorter the time taken for the bubble to rise is. The change in the flow field seems to be mainly caused by the vibration of fluid particles, almost independent of the level of gravity. The flow field becomes more chaotic as A/D and Bo increase.