DIFFUSIONAL EFFECT OF PORES ON THE DENSIFICATION IN MICROGRAVITY LIQUID PHASE SINTERED FE-CU ALLOYS

OLiPSE-02 Fe-Cu samples, which were liquid phase sintered under 10 -5 torr in microgravity for 20, 30, 60, and 330 min for each composition, were analyzed in this article. The compositions of the samples are 80% Fe/Cu, 70% Fe/Cu, 60% Fe/Cu, and 50% Fe/Cu by volume. The experimental results of distortion and densification were presented. During the microgravity processing, liquid ejection occured for the long duration samples with compositions 70% Fe/Cu and 60% Fe/Cu. Measurements of the weights and dimensions of all the beads were made and their distributions were presented. One of the beads that are about the average weight and size from the 70% Fe/Cu long duration sample was chosen to be mounted, polished, etched, and analyzed under an optical microscope. The iron in the bead appeared as iron grains and its grain size was smaller than that in the mother sample with the same composition. Discussions of the bead and its iron grain formations are provided.     

Experiments on microgravity boiling heat transfer by using transparent heaters

To clarify the relation between the liquid–vapor behavior and the heat transfer characteristics in the boiling phenomena, the structures of transparent heaters were developed for both flow boiling and pool boiling experiments and were applied to the microgravity environment realized by the parabolic flight of aircraft. In the flow boiling experiment, a transparent heated tube makes the heating, the observation of liquid–vapor behavior and the measurement of heat transfer data simultaneously possible. The heat transfer coefficient in the annular flow regime at moderate quality has distinct dependence on gravity provided that the mass velocity is not so high, while no noticeable gravity effect is seen at high quality and in the bubbly flow regime. The measured gravity effect was directly related to the behavior of annular liquid film observed through the transparent tube wall. In the pool boiling experiment, a structure of transparent heating surface realizes both the observation of the macrolayer or microlayer behavior from underneath and the measurements of local surface temperatures and the layer thickness. It was clarified in the microgravity experiments that no vapor stem exists but tiny bubbles are observed in the macrolayer underneath a large coalesced bubble at high heat flux. The heat flux evaluated by the heat conduction across the layer assumes less than 30% of the total to be transferred. The evaporation of the microlayers underneath primary bubbles just after the generation dominates the heat transfer in the microgravity, not only in the isolated bubble region but also in the coalesced bubble region.     

Thermovibrational Convection in Microgravity: Preparation of a Parabolic Flight Experiment

This work describes the preparation of the future experiments on thermovibrational convection in microgravity during parabolic flights. The experimental setup for observing thermovibrational flows is designed. It consists of a cubic cell with liquid, which is subjected to controlled vibration, and equipment for registering velocity and temperature fields with a help of optical digital interferometry. The question of choosing working liquid and control parameters of the experiment is addressed. A 3D numerical simulation of thermovibrational convection in a cubic cavity is performed for real parabolic flight conditions. The study is aimed at estimating the values of physical quantities that manifest the presence of thermovibrational flows and can be experimentally measured during short microgravity time (20 s).     

真空微重力熔炼高锂含量铝锂合金

利用电磁模拟微重力装置熔炼高锂含量铝锂合金。试验结果表明：Li的质量分数为5％～10％时不产生偏析；合金密度达到了超轻合金的密度范围。通过改进坩埚结构、加热方法、热处理工艺等措施，合金的性能接近已实际应用的8090合金。     

A DIFFERENTIAL APPROACH TO HEAT PIPE PRIMING IN MICROGRAVITY

Presented here is a study of the forces governing the liquid and vapor flow, in an external artery heat pipe. A differential analysis was performed on the heat pipe based upon the continuity and momentum equations.

Using these fundamental equations, a computer model was developed, capable of predicting the fluid motion resulting from the surface tension and viscous frictional forces in a microgravity environment. The model used a nested iterative technique to first establish the pressure distribution along the longitudinal axis of the heat pipe for a known displacement. Then the time necessary, for a given fluid to initially assume or return to the configuration required for proper operation was calculated.

In addition to providing an estimate of the required priming time, the model predicted that priming could be prematurely terminated. Comparisons of the predicted priming time and priming limitations were made with the results of an experimental test package flown on the NASA KC-135 Zero-g aircraft. The results of this comparison helped to establish the accuracy of the modeling techniques.     

Chemical oven technology and its application in AlN composites fabricated under microgravity condition

The microgravity experiments of fabrication materials by using TiC chemical ovens have been performed on the parabolic flight plane. The gravity behaviors in the combustion reactions of chemical ovens themselves during the aircraft parabolic flight were investigated. The results show that, the combustion temperatures and reactions vary with different gravity levels. These influences are related with the function of gravity on the molten titanium. As an example of the application of chemical ovens, the first and preliminary investigation of AlN-borosilicate glass composites fabricated in the chemical ovens during aircraft parabolic flights is conducted. The results indicate that, microgravity condition allows the synthesis of AlN-borosilicate glass composite with improved microstructure as compared with that on the ground.     

Characteristics of turbulent nonpremixed jet flames under normal- and low-gravity conditions

An experimental study was performed with the aim of investigating the structure of transitional and turbulent nonpremixed jet flames under different gravity conditions. Experiments were conducted under three gravity levels, viz., 1 g, 20 mg, and 100 μg. The milligravity and microgravity conditions were achieved by dropping a jet-flame rig in the University of Texas at Austin 1.25-s and NASA-Glenn Research Center 2.2-s drop towers, respectively. The flames studied were piloted nonpremixed propane, ethylene, and methane jet flames at source Reynolds numbers ranging from 2000 to 10,500. The principal diagnostic employed was time-resolved cinematographic imaging of the visible soot luminosity. Mean and root-mean-square (RMS) images were computed, and volume rendering of the image sequences was used to investigate the large-scale structure evolution and flame tip dynamics. The relative importance of buoyancy was quantified with the parameter, ξL, as defined by Becker and Yamazaki (Combust. Flame 33 (1978) 123-149). The results showed, in contrast to some previous microgravity studies, that the high-Reynolds-number flames have the same flame length irrespective of the gravity level. The mean and RMS luminosity images and the volume renderings indicate that the large-scale structure and flame tip dynamics are essentially identical to those of purely momentum-driven flames provided ξL is less than approximately 2-3. The volume renderings show that the luminous structure velocities (i.e., celerities) normalized by the jet exit velocity are approximately constant for ξL<6, but scale as for ξL>8. The flame length fluctuation measurements and volume renderings also indicate that the luminous structures are more organized in low gravity than in normal gravity. Finally, taken as a whole, this study shows that ξL is a sufficient parameter for quantifying the effects of buoyancy on the fluctuating and mean characteristics of turbulent jet flames.     

Titanosilicate ETS-10 as a Lewis acid catalyst in the Meerwein–Ponndorf–Verley (MPV) reaction

The potential of ETS-10 as a Lewis acid catalyst was investigated using the MPV reaction at one atmosphere total pressure and 273 K. ETS-10 was hypothesized to be a potential Lewis acid catalyst as it has titanium in octahedral symmetry, which is the symmetry shown in zeolite Beta to be the most active site for the Lewis acid catalyzed Meerwein–Ponndorf–Verley (MPV) reaction. The MPV reaction is a hydrogen transfer reaction that can be used for obtaining information about the structure and performance of catalysts by comparing the product selectivities and catalytic activities. Due to their similar structures, the catalytic activity of ETS-10 was compared to zeolite Beta samples that were space-grown (flight, fewer defects) and to their earth-grown terrestrial controls. The higher tr-alcohol selectivity (i.e., trans-4-tert-butylcyclohexanol, ∼80% vs. 40%) observed over ETS-10 was attributed to a larger volume being available in the pores of ETS-10 compared to the zeolite Beta samples. By-product formation (i.e., 4-tert-butylcyclohexene) was significantly less over ETS-10 (∼5%) in comparison with the zeolite Beta samples (flight and control; ∼35%). These results reaffirm the octahedral symmetry as the Lewis active site for the MPV reaction, and illustrate that ETS-10 is a good catalyst for MPV type reactions.     

Raman Spectroscopic Analysis of Cupriavidus metallidurans LMG 1195 (CH34) Cultured in Low-shear Microgravity Conditions

In this study, the effect of low-shear microgravity on the metabolism of Cupriavidus metallidurans LMG 1195 was studied with Raman spectroscopy. Therefore, the strain was cultured for 24 or 48 h in a rotating wall vessel to simulate microgravity (SMG) and in a control setup. The differences in Raman spectra recorded from both setups after 24 h of culturing were small. The most prominent features in a difference spectrum, calculated between the mean spectra from the microgravity and the control setup separately, could be assigned to the presence of poly-β-hydroxybutyrate (PHB). SMG seems to yield a higher PHB production after 24 h of culturing. Additional processing of the spectra suggested that SMG induced also other changes in the carbon-metabolism. After 48 h, similar results were found for the carbon metabolism, while PHB concentrations were reduced in SMG compared to the control. However, these differences could also be caused by interfering effects that may occur in the bioreactors after a prolonged incubation time.     

CFD simulation of heat transfer and phase change characteristics of the cryogenic liquid hydrogen tank under microgravity conditions

The heat transfer and phase change processes of cryogenic liquid hydrogen (LH₂) in the tank have an important influence on the working performance of the liquid hydrogen-liquid oxygen storage and supply system of rockets and spacecrafts. In this study, we use the RANS method coupled with Lee model and VOF (volume of fraction) method to solve Navier-stokes equations. The Lee model is adopted to describe the phase change process of liquid hydrogen, and the VOF method is utilized to calculate free surface by solving the advection equation of volume fraction. The model is used to simulate the heat transfer and phase change processes of the cryogenic liquid hydrogen in the storage tank with the different gravitational accelerations, initial temperature, and liquid fill ratios of liquid hydrogen. Numerical results indicate greater gravitational acceleration enhances buoyancy and convection, enhancing convective heat transfer and evaporation processes in the tank. When the acceleration of gravity increases from 10^?2 g0 to 10^?5 g0, gaseous hydrogen mass increases from 0.0157 kg to 0.0244 kg at 200s. With the increase of initial liquid hydrogen temperature, the heat required to raise the liquid hydrogen to saturation temperature decreases and causes more liquid hydrogen to evaporate and cools the gas hydrogen temperature. More cryogenic liquid hydrogen (i.e., larger the fill ratio) makes the average fluid temperature in the tank lower. A 12.5% reduction in the fill ratio resulted in a decrease in fluid temperature from 20.35 K to 20.15 K (a reduction of about 0.1%, at 200s).