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"reduced gravity"
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Here there be dragonflies
\"Now a fugitive, Willa leaves Chicago and goes on the run! But when she takes refuge with some low-G farmers, she stumbles into a plot to attack the city. Oh, and on top of all that: giant, man-eating bugs! Maybe we should have led with that.\" -- Provided by the publisher.
Book
Gravity-Induced Distortion During Liquid-Phase Sintering
Sintering is used in the production of complex-shaped engineering components from compacted powders. For most applications, a predictable sintered size is a key requirement. While the formation of a liquid phase can accelerate sintering, it also can contribute to nonuniform dimensional change resulting in component distortion. Several factors, including gravity, play a role with respect to distortion. These factors are examined using tungsten heavy alloys sintered in two gravitational environments where liquid content, pore saturation with liquid, and loss of capillarity result in distortion. A significant situation arises when the component loses structural rigidity, as occurs with a low dihedral angle and high liquid content. In microgravity sintering, where buoyancy forces are absent, pores coalesce to cause swelling, leading to incomplete densification, and in some cases extensive distortion. Sintering on Earth increases solid grain contact, resulting in greater densification and less distortion. Microgravity liquid-phase-sintering behavior is substantially different from that exhibited by Earth-based sintering trials.
Journal Article
Skyward. Volume one, 'My low-G life'
\"One day, gravity on Earth suddenly became a fraction of what it is now. Twenty years later, humanity has adapted to its new low-gravity reality. And to Willa Fowler, who was born just after G-day, it's pretty awesome. You can fly through the air! I mean, sure, you can also die if you jump too high. So you just don't jump too high. And maybe don't get mixed up in your dad's secret plan to bring gravity back that could get you killed... From writer Joe Henderson (showrunner of Fox's Lucifer) and artist Lee Garbett (Lucifer, Loki: Agent of Asgard) comes the story of a young woman's journey to find her place in a world turned upside down.\"--Publisher's description.
Book
In Situ Study of Peritectic Couple Growth Under Purely Diffusive Conditions
Herein, in a microgravity campaign onboard the International Space Station, peritectic coupled growth (PCG) is studied by solidifying alloys of the peritectic transparent organic system TRIS–NPG under purely diffusive conditions. The experiment reveals that the formation of PCG begins with coagulated lateral bands comprising the peritectic phase at temperatures below the peritectic one. After reaching the growth front of the pro-peritectic phase, growth competition between both solid phases occurs such that the patches of the pro-peritectic phase, lamellae, and fibers/rods grow in the stated order, coupled with the peritectic phase. As the entire solidification process occurs during the initial transient stage, the diffusion coupling between the two solid phases is weak. With the gradual decrease in the interface temperature during the initial transient, the necessary growth conditions for the pro-peritectic phase diminish. Additionally, different concentrations along the inclined solid/liquid interface favor the peritectic phase at the rear window and the pro-peritectic phase at the front window. The corresponding PCG lasts 19 hours while the recoil of the inclined interface continues to a temperature level that makes alterations of the ‘effective’ TRIS–NPG phase diagram necessary.
Journal Article
Thermophysical Properties Measurement of Al–22.5 wt pctCu in Reduced Gravity Using the ISS-EML
A hypoeutectic Al–22.5 wt pctCu sample was processed using the Electro-Magnetic Levitator on board of the International Space Station within the frame of the European Space Agency projects NEQUISOL and THERMOLAB. In total, 21 cycles of melting and cooling were carried out, with the last cycle yielding a primary undercooling of 20 K and a eutectic undercooling of 35 K. The density, surface tension, and viscosity of the liquid sample were measured using the oscillating drop method and a high-speed camera. The evolution of the temperature was recorded with a pyrometer. The oscillations of the drop appear modulated, indicative of a nonlinear behavior caused by rotation, precession, nutation of the sample, and high initial deformation. Nevertheless, the measurements are in line with previous experimental results for alloys of similar composition and with theoretical predictions. These results highlight the potential of the method to build an extensive and reliable database of the thermophysical properties of pure metals and alloys.
Journal Article
Nucleation and Growth Dynamics of Equiaxed Dendrites in Thin Metallic Al–Cu and Al–Ge Samples in Microgravity and on Earth
In this study, the nucleation and growth characteristics of equiaxed dendrites in near-isothermal solidification experiments, performed during two sounding rocket missions, MAPHEUS-6 and 7, are investigated. Two samples of the composition Al–15 wt pct Cu and one sample of the composition Al–46 wt pct Ge were processed in microgravity and several samples on ground. In situ X-radiography was performed to observe the nucleation dynamics and microstructure evolution during solidification of the 200 µm thin, disc-shaped samples. The measured dendritic growth rates and observed concentration distributions in the liquid indicate no difference between microgravity and on-ground horizontal experiments, in line with previous observations. On the contrary, a difference in the nucleation behavior was found. In all microgravity experiments bursts of nucleation were observed, which is different from comparable on-ground solidification experiments, where the nucleation occurs continuously. The combined analyses suggest that small variations of the concentration fields that probably originate from convective flow and buoyancy of the grains in the on-ground experiments, lead to a spatially variable nucleation undercooling distribution and hence to continuous nucleation. In contrast, the absence of convective flow in microgravity results in a more uniform nucleation undercooling distribution. The grains therefore nucleate in bursts at the surface walls, when the necessary nucleation undercooling is reached.
Journal Article
Relating Cooling Rates in Superheated Liquid During Solidification for Powder Characterization
When doing mathematical modeling to predict microstructural evolution during spray-forming processes, it is important to know how fast cooling occurs during solidification. Radiative, convective, and conductive heat losses are always present, and it is relatively straightforward to define cooling in the liquid phase. However, once solid begins to form, it is difficult to evaluate the mushy-zone cooling rates because both sensible and latent heat are removed simultaneously. Since mushy-zone cooling drives microstructural evolution, it is important to be able to relate liquid and solid cooling processes. A model is developed relating these two cooling rates as a function of melt thermophysical properties and includes the ability to predict how radiative transport is influenced by any phase change-induced variation in surface emissivity or specific heat. It is validated using containerless processing techniques developed for use during space testing using the ESA ISS-EML facility. The motivation of this paper is to bridge the gap between cooling rates observed in the liquid and rates which subsequently develop during mushy-zone solidification.
Journal Article
The Transient Evolution of Flow Due to the Excitation Pulse in Oscillating Drop Experiments in Microgravity Electromagnetic Levitation
In oscillating drop experiments, surface oscillations in a molten sample are captured and analyzed to determine the surface tension and viscosity of a melt without the need to contact the liquid sample. In electromagnetic levitation, surface oscillations are initiated using an excitation pulse in the electromagnetic field. The variation in the electromagnetic force field drives rapid acceleration in the melt while also changing the flow pattern. During the quasi-static flow conditions prior to the excitation pulse, the flow displays a “positioner-dominated” flow pattern with 4 recirculation loops in the sample hemisphere. However, the accelerating flow of the excitation pulse transitions into a “heater-dominated flow” pattern in which there are only 2 recirculation loops in the sample hemisphere. Following the excitation pulse, the flow rapidly slows and quickly returns to the conditions present before the excitation pulse. For many combinations of parameters, the transition in the flow pattern results in a very complicated variation in velocity with time; that variation is the topic of this paper.
Journal Article
Flow control of thermal convection using thermo electro hydrodynamic forces in a cylindrical annulus
The main topic of this thesis is the influence of the dielectrophoretic (DEP) force on a thermal convection in a cylindrical annulus under microgravity conditions of parabolic flights. To perform these experiments a specialized experimental setup was designed. The annulus is differentially heated to create a temperature gradient and an ac voltage of up to 10kV is applied. Two different experiment setups were build for different measurement methods. One for Shadowgraph and Synthetic Schlieren methods and the other for PIV measurements. Several complex flow patterns can be identified by combining the resulting images from both visualization mthods. The heat transfer is determined under different experimental conditions. Under the given conditions it is possible to make a correlation between the flow patterns and the level of the convective heat transfer. The experimental data is compared to theoretical data from a linear stability analysis. The patterns predicted by the can also found in the experiments.
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