Taking Plateau into Microgravity: The Formation of an Eightfold Vertex in a System of Soap Films

The microgravity phases of parabolic flights were used to perform experiments with soap films trapped in wire frames, a variation of the wire frame experiments originally designed by the nineteenth century Belgian scientist Joseph Plateau. We considered the formation of an eightfold vertex of Plateau borders within a cubic frame. In terrestrial experiments such a vertex can only be formed when liquid is forced through the Plateau borders, but in microgravity we found this vertex to be stable under equilibrium (non-flow) conditions once the liquid volume fraction exceeds 0.022 ± 0.005. This is consistent with the theoretical value for the transition, which for our experiment we estimate to be 0.0192.     

Microgravity experiments on flame spread along fuel-droplet arrays using a new droplet-generation technique

A new droplet-array generation technique achieved high quality and high reliability in microgravity experiments on multiple-droplet combustion. Each fuel droplet formed at the intersection of fine, X-shaped SiC fibers when liquid fuel was supplied through a fine glass tube. We aligned several sets of these X-shaped fibers and their corresponding fine glass tubes to form a droplet array. All the droplets in the array were simultaneously generated in a short time. In flame-spread experiments, a hot-wire igniter ignited an end droplet to initiate the flame spread along the array. We demonstrated microgravity experiments of droplet array combustion using the new droplet-array generation technique at a drop-experiment facility, MGLAB, in Japan. We successfully generated large droplets, which often fell off the fiber intersection in normal gravity, by using this method in microgravity. This technique is also effective in droplet-array combustion experiments using high-volatility fuel, where prevaporization is substantial. We compared the flame-spread rate and the flame-spread limit of these linear droplet arrays with results of an existing experiment, and discussed the effects of the suspending fiber on the flame spread.     

Laminar burning velocities and Markstein lengths of premixed methane/air flames near the lean flammability limit in microgravity

Effects of flame stretch on the laminar burning velocities of near-limit fuel-lean methane/air flames have been studied experimentally using a microgravity environment to minimize the complications of buoyancy. Outwardly propagating spherical flames were employed to assess the sensitivities of the laminar burning velocity to flame stretch, represented by Markstein lengths, and the fundamental laminar burning velocities of unstretched flames. Resulting data were reported for methane/air mixtures at ambient temperature and pressure, over the specific range of equivalence ratio that extended from 0.512 (the microgravity flammability limit found in the combustion chamber) to 0.601. Present measurements of unstretched laminar burning velocities were in good agreement with the unique existing microgravity data set at all measured equivalence ratios. Most of previous 1-g experiments using a variety of experimental techniques, however, appeared to give significantly higher burning velocities than the microgravity results. Furthermore, the burning velocities predicted by three chemical reaction mechanisms, which have been tuned primarily under off-limit conditions, were also considerably higher than the present experimental data. Additional results of the present investigation were derived for the overall activation energy and corresponding Zeldovich numbers, and the variation of the global flame Lewis numbers with equivalence ratio. The implications of these results were discussed.     

Nucleation and growth of electrolytic gas bubbles under microgravity

The evolution of oxygen gas bubbles in potassium hydroxide solution is observed in situ under microgravity by a charge-coupled device camera, focusing on the wettability of a platinum electrode modified by thiol self-assembled monolayers. Single bubble measurements on the microwire electrode reveal a three-step growth process involving (1) the nucleation and formation of a supersaturated layer of dissolved gas followed by (2) a rapid growth phase depending on the gas diffusion process, and finally, (3) a stable growth phase where the growth rate is dominated by the bubble configuration depending on the contact angle. Moreover, correlation of multiple gas bubble observations with electrochemical data and surface coverage on the plate electrode reinforce the important role of wettability in determining bubble motion and energy consumption during electrolysis under microgravity.     

Measurement and use of the vertical gravity gradient in correcting repeat microgravity measurements for the effects of ground subsidence in geothermal systems

Changes in mass resulting from production and reinjection in geothermal fields can be monitored using repeat microgravity measurements. The measured changes in gravity, however, need to be corrected for the effects of any exploitation-induced ground subsidence. The correction required at each measurement point is the product of the amount of ground subsidence and the vertical gravity gradient at that point. Measurements of the gravity gradient, made using a portable tower, show that it varies from place to place depending mainly on the local topography. Measured gradients, in areas of high subsidence rate, range between −276 and −339 μgal/m at 30 sites in the Wairakei–Tauhara field and between −296 and −321 μgal/m at nine sites in the Ohaaki field (New Zealand). These values are similar to those used previously. At 37 sites measured in the Yanaizu–Nishiyama field (Japan) the gradient varied between −244 and −352 μgal/m. Measurements at six sites showed no significant change in gravity gradient with height above the ground surface; a single value for the gradient can therefore be used at each site to correct for the gravitational effect of any ground movement. Calculations show the effects on the vertical gravity gradient of groundwater level variations, mass changes associated with the ground subsidence, and reservoir mass changes are negligible at Wairakei.     

China’s Recoverable Satellites and Their Onboard Experiments

Twenty-three recoverable satellites have been successfully launched in China since 1975. A number of microgravity experiments were successfully performed by utilizing the piggyback capability of the satellite together with other tasks of the previous flights. This paper presents firstly an overview of the recoverable satellite development in China. Main characteristics of Chinese recoverable satellites and the onboard scientific experiments are then discussed. The environment, support, and the interface between the working payload and satellite during different design and manufacture phases are also briefly described, followed by future trends of platform technology and potential applications.     

A Novel Counter Sheet-flow Sandwich Cell Culture Device for Mammalian Cell Growth in Space

Cell culture and growth in space is crucial to understand the cellular responses under microgravity. The effects of microgravity were coupled with such environment restrictions as medium perfusion, in which the underlying mechanism has been poorly understood. In the present work, a customer-made counter sheet-flow sandwich cell culture device was developed upon a biomechanical concept from fish gill breathing. The sandwich culture unit consists of two side chambers where the medium flow is counter-directional, a central chamber where the cells are cultured, and two porous polycarbonate membranes between side and central chambers. Flow dynamics analysis revealed the symmetrical velocity profile and uniform low shear rate distribution of flowing medium inside the central culture chamber, which promotes sufficient mass transport and nutrient supply for mammalian cell growth. An on-orbit experiment performed on a recovery satellite was used to validate the availability of the device.     

Effect of microgravity on flow boiling heat transfer of liquid hydrogen in transportation pipes

The flow boiling phenomenon of liquid hydrogen (LH2) during transportation in microgravity is very different from that under terrestrial condition. In this study, a saturated flow boiling of LH2 in a horizontal tube has been simulated under microgravity condition using coupled level-set and volume of fluid method. The validation of the developed model shows good agreement with the experimental data from the literature. The changes of heat fluxes and pressure drops under different gravitational accelerations were analyzed. And, the variation of heat fluxes with different wall superheat and contact angle were compared between microgravity (10⁻⁴g) and normal gravity (1g) condition. Also, the influence of surface tension were studied under microgravity. The numerical results indicate that the heat flux decrease with the decrement of gravitational acceleration. And the heat transfer ratio decrease with the increment of wall superheat in the nucleate boiling regime. The heat transfer slightly reduce when considering surface tension. In addition, the changes of contact angle have a more significant impact on heat transfer under microgravity condition.     

空间细胞生物学研究进展

空间生物学逐渐成为生物学、航天医学等领域的研究热点问题之一。本文主要围绕微重力对细胞的影响进行综述。文中首先介绍了空间细胞培养的实验方式,指出多种空间因素对细胞生长会产生影响,着重论述了微重力对细胞生长的作用特点。根据动物细胞在空间搭载和地基模拟条件下细胞形态和生理指标的变化进行分类,对已取得的有代表性的实验结果进行归纳、总结,为建立数学模型和仿真分析等实验提供一定的指导义。