微重力环境下蜡烛火焰与油滴沉降的实验研究

搭建了短时微重力实验系统,对微重力条件下蜡烛火焰与油滴沉降进行了实验观测,帮助学生理解微重力环境下的物理规律与实验现象.     

Fullerit C<Subscript>60</Subscript> single crystals grown on earth and in space

Fullerit C₆₀ single crystals were grown by sublimation on Earth and under microgravity during the FOTON-M3 mission using the same growth parameters and the same multizoned electrovacuum POLIZON-M furnace. IR spectroscopy and X-ray measurements revealed the considerably better crystal structure of the crystals grown under microgravity.     

Review: Experiments in Fundamental Physics Scheduled and in Development for the ISS

This is a review of those experiments in the area of Fundamental Physics that are either approved by ESA and NASA, or are currently under development, which are to be performed in the microgravity environment of the International Space Station. These experiments cover the physics of liquid Helium (SUE, BEST, MISTE, DYNAMX, and EXACT), ultrastable atomic clocks (PHARAO, PARCS, RACE), ultrastable microwave resonators (SUMO), and particle detectors (AMS and EUSO). The scientific goals are to study more precisely the universality properties of liquid Helium under microgravity conditions, to establish better time standards and to test the universality of the gravitational red shift, to make more precise tests of the constancy of the speed of light, and to measure the particle content in space directly without disturbances from the Earth's inner atmosphere.     

Modeling of one-dimensional smoldering of polyurethane in microgravity conditions

Results are presented from a model of forward smoldering combustion of polyurethane foam in microgravity. The transient one-dimensional numerical-model is based on that developed at the University of Texas at Austin. The conservation equations of energy, species, and mass in the porous solid and in the gas phases are numerically solved. The solid and the gas phases are not assumed to be in thermal or in chemical equilibrium. The chemical reactions modeled consist of foam oxidation and pyrolysis reactions, as well as char oxidation. The model has been modified to account for new polyurethane kinetics parameters and radial heat losses to the surrounding environment. The kinetics parameters are extracted from thermogravimetric analyses published in the literature and using Genetic Algorithms as the optimization technique. The model results are compared with previous tests of forward smoldering combustion in microgravity conducted aboard the NASA Space Shuttle. The model calculates well the propagation velocities and the overall smoldering characteristics. Direct comparison of the solution with the experimental temperature profiles shows that the model predicts well these profiles at high temperature, but not as well at lower temperatures. The effect of inlet gas velocity is examined, and the minimum airflow for ignition is identified. It is remarkable that this one-dimensional model with simplified kinetics is capable of predicting cases of smolder ignition but with no self-propagation away from the igniter region. The model is used for better understanding of the controlling mechanisms of smolder combustion for the purpose of fire safety, both in microgravity and normal gravity, and to extend the unique microgravity data to wider conditions avoiding the high cost of space-based experiments.     

微重力环境下液体表面张力的实验观察与研究

在微重力环境中,重力的作用几乎消失,液体的表面张力起主导作用,微重力下液体的流动特性和平衡界面也会产生显著变化．为了使学生们能更真切、更直观地观察到微重力下的奇妙现象,我们搭建了短时微重力系统并开展了一些实验演示与观测研究．通过微重力系统模拟微重力环境,可以清楚地观察到液体表面的变化,更有助于同学们深入了解微重力下的物理规律和实验现象,对于激发同学们认识和发现新的规律和总结新的定律具有重要意义．     

用高空气球搭载微重力实验研究浮力对预混V形火焰的影响

在地面实验中观测到的燃烧现象,包含了浮力的影响。利用微重力实验在浮力消失后研究火焰,有助于深入理解燃烧过程。本文介绍了利用高空气球搭载微重力实验对甲烷－空气预混Ｖ形火焰的研究。实验提供了长时间微重力环境下火焰的动态图像。利用计算机图像处理方法对火焰图像的分析表明,在本实验的工况下,微重力下预混Ｖ形火焰锋面的张角比正常重力下变大,皱折和摆动加剧。这说明浮力确实影响预混燃烧过程。     

Condensation of cosmic analog material in microgravity conditions: Preliminary analysis of a first set of flights

Summary In this paper we give a brief summary of the first results obtained in the frame of the STARDUST project. The aim of the experiment is to simulate the condensation of cosmic-dust analog materials under microgravity conditions. This approach will allow to reproduce actual condensation processes active in space better than in the laboratory experiments performed so far. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Methods for improving the microgravity environment onboard automatic spacecrafts for microgravity investigations

It is shown that none of the domestic spacecrafts on which microgravity experiments can be performed satisfy the requirements for experiments on the physics of liquid and space materials science by the level of their onboard microgravity environment. The necessary level of microgravity environment for such experiments is ～10^?7 g ₀. Procedures for decreasing the microgravity onboard a prospective spacecraft intended for microgravity studies to a level necessary level are proposed.     

微重力环境利用

文章阐述了微重力条件下的流体物理基本现象的研究,包括流体和体积输运,扩散与质量输运,毛细与润湿、固化、成核与过冷、临界现象以及学科的相关性。继之,简要介绍了微重力实际应用,包括：太空材料加工,各咱晶体生长,金属与合金、复合材料、玻璃等加工工艺;燃烧与微重力问题;生命科学中微重力利用问题（另文发表）。其间,顺便讨论了航天技术发展对微重力科学的推进与限制,针对我国卫星应用这个课题,以理论联系实际的方法进行分析评价。该文是对《微重力实验环境》一文（见１９９８年第７期《物理》）的补充。     

The importance of thermal radiation transfer in laminar diffusion flames at normal and microgravity

The importance of radiation heat loss in laminar and turbulent diffusion flames at normal gravity has been relatively well recognized in recent years. There is currently lack of quantitative understanding on the importance of radiation heat loss in relatively small scale laminar diffusion flames at microgravity. The effects of radiation heat transfer and radiation absorption on the structure and soot formation characteristics of a coflow laminar ethylene/air diffusion flame at normal- and microgravity were numerically investigated. Numerical calculations were conducted using GRI-Mech 3.0 combustion chemistry without the NO_x mechanism and complex thermal and transport properties, an acetylene based soot formation model, and a statistical narrow-band correlated-k non-grey gas radiation model. Radiation heat transfer and radiation absorption in the microgravity flame were found to be much more important than their counterparts at normal gravity. It is important to calculate thermal radiation transfer accurately in diffusion flame modelling under microgravity conditions.     

微重力环境中的蜡烛火焰

对蜡烛火焰动态特征的分析表明,从正常重力状态过渡到微重力状态,火焰的空气动力学特征比质量和能量的传输特征的变化快。通过一台差分干涉仪首次测量得到了微重力环境中蜡烛火焰的温度。结果表明,微重力蜡烛火焰的温度小于正常重力蜡烛火焰的温度。微重力蜡烛火焰之所以呈蓝色是因为其温度小于烟黑生成的阈值温度1300K。但当环境氧浓度足够高时,火焰温度大于烟黑生成的阈值温度,火焰中明显有烟黑生成,颜色为亮黄色。     

Some results of the growth of semiconductor crystals in microgravity conditions (to the 50th anniversary of Yuri Gagarin’s flight into space)

The history of the growth of semiconductor crystals aboard space vehicles and their subsequent investigation has been described shortly. It has been shown using Ge(Ga), GaSb(Si), and GaSb(Te) crystals as an example that the formation of segregation growth striations can be avoided during their recrystallization by the vertical Bridgman method in conditions of physical simulation of microgravity on the Earth, mainly due to the essential weakening of the thermal gravitation convection. By their structure and impurity distribution, they approach the crystals grown in space. The investigation of recrystallization of Te has made it possible to determine the role of the detachment effect characteristic of the microgravity conditions and the features of the microstructure of the samples that crystallize with a free surface. The analysis of the results obtained from experiments in space allows us to better understand the processes occurring during the crystallization of the melts and to improve the crystal growth in terrestrial conditions.     

不同重力下窄通道内薄材料表面的火焰传播

在常重力下模拟微重力燃烧对载人航天器的火灾安全具有重要意义.窄通道就是这样一种可以有效限制自然对流的模拟设施.但是,不同重力下火焰传播的相似性仍然是有待研究的问题.本文用实验和数值模拟的方法,比较了不同重力下有限空间内热薄材料表面的逆风传播火焰.不同重力下火焰形状和火焰传播速度的比较表明,1cm高的水平窄通道可以有效地限制自然对流,在常重力下用这种通道能够模拟微重力下相同几何尺寸的通道中的火焰传播.因此,在地面上首先利用水平窄通道,模拟相同环境中的微重力火焰传播,然后考虑通道尺寸变化对火焰传播的影响,有可能成为地面模拟其他尺寸的空间中的微重力燃烧的方法.     

Gravity effects on partially premixed flames: an experimental-numerical investigation

While premixed and nonpremixed microgravity flames have been extensively investigated, the corresponding literature regarding partially premixed flames (PPFs) is sparse. We report the first experimental investigation of burner-stabilized microgravity PPFs. Partially premixed flames with multiple reaction zones are established in microgravity on a Wolfhard–Parker slot burner in the 2.2 s drop tower at the NASA Glenn Research Center. Microgravity measurements include flame imaging, and thermocouple and radiometer data. Detailed simulations are also used to provide further insight into the steady and transient response of these flames to variations in g. The flame topology and interactions between the various reaction zones are strongly influenced by gravity. The flames widen substantially in microgravity. During the transition from normal to microgravity, the flame structure experiences a fast change and another relatively slower transient change. The fast response is due to the altered advection as the value of g is reduced, while the slow response is due to the changes in the diffusive fluxes. The radiative heat loss from the flames increases in microgravity. A scaling analysis based on a radiation Damköhler number is able to characterize the radiation heat loss.     

Image of a gaseous discharge in microgravity

The electrode gap length of a gaseous discharge in a low-pressure 1 g environment is compared with its length in a low-pressure microgravity environment for pressures ranging from 30 kPa to atmospheric pressure. The maximum gap length obtained is measured for both conditions using three separate gases. Video images of the discharge in microgravity make apparent both the lack of gravity-induced convection, which gives rise to the arching of the 1 g discharge, and the increase in gap length     

Onset of superfluidity far from equilibrium: dynamical effects on the correlation length

Nonlinear heat conduction has recently been measured near the superfluid transition in pure ⁴He at very low heat flux Q. Since both dynamic effects and gravity limit the divergence of the superfluid correlation length near the transition at low-Q, these measurements must be repeated in the microgravity environment in order to observe the dynamic effects in isolation. Comparison of the microgravity data to similar data obtained on Earth will provide experimental insight into the effect of gravity on this nonlinear conduction region at low heat flux where theoretical predictions are lacking. While some measurement advantages exist in the microgravity laboratory, it is the study of the direct effect of gravity on the nonlinear conduction measurements that motivate the microgravity need.     

微重力下低温贮箱压力控制技术进展

针对微重力下低温贮箱压力升高的问题,简要介绍了几种常用的低温贮箱压力控制的方法及原理,讨论了它们各自存在的问题,并简要展望未来低温贮箱压力控制技术的发展方向。文章指出,未来研究重点在于将主动制冷与被动绝热相结合,实现零蒸发贮存的热转移技术。     

近贫燃极限甲烷/空气火焰的层流燃烧速度研究

利用微重力条件下向外传播的球形火焰,对贫燃极限附近甲烷/空气预混火焰的层流燃烧速度进行了测量,得到当量比从0.512(本文微重力实验中测定的可燃极限)到0.601范围内的零拉伸层流燃烧速度,并与前人实验数据和使用3种化学反应动力学模型的计算结果进行了比较.本文实验结果与已有的微重力实验数据非常接近,而其他研究者在常重力...     

The effects of microgravity on nanoparticle size distributions generated by the ultrasonic reduction of an aqueous gold-chloride solution

A solution of gold chloride was reduced using ultrasound irradiation to prepare metallic gold nanoparticles under conditions of microgravity and normal gravity at sea level. Particle size distributions were measured using TEM analysis. A mean particle diameter of 10 nm was obtained in microgravity while a mean diameter of 80 nm was obtained in the laboratory. Absorbance measurements on the reacted solution found an enhanced reduction rate in the reduction of gold chloride in microgravity compared to that in the laboratory.     

窄通道内热薄燃料表面火焰传播特性研究

利用实验和数值模拟对微重力和常重力条件下高度为14mm和10mm的窄通道内热薄纸张表面火焰传播特性进行了研究。不同重力条件下窄通道内火焰传播速度随气流速度变化的规律符合得较好,说明地面窄通道实验能够模拟微重力条件下材料表面火焰传播的主要特征。地面窄通道中浮力流动速度的最大值约为5cm／s,与常规实验通道（高度较大）相比...