Microgravity experiments on flame spread along fuel-droplet arrays at high temperatures

Microgravity experiments on droplet-array combustion were conducted under high-ambient-temperature conditions. n-Decane droplet arrays suspended on SiC fibers were inserted into a high-temperature combustion chamber and were ignited at one end to initiate the flame spread in high-temperature air. Flame-spread modes, burning behavior after the flame spread, and flame-spread rate were examined at different ambient temperatures. Experimental results showed that the appearance of flame-spread modes and the flame-spread rate were affected by the ambient temperature. The flame-spread rate increased with the ambient temperature. These facts are discussed based on the temperature effects on the droplet heating and the development of a flammable-mixture layer around the next droplet. A simple model was introduced to analyze these effects. The effects of the ambient temperature on the appearance of group combustion of the array after the flame spread and the scale effect in the flame spread are also discussed.     

微重力条件下用于低温燃料贮箱的热动力排气系统

简要介绍一种可供选择使用的低温燃料贮箱零重力排气系统。介绍了该系统的功能及工作原理，给出了热交换器混合泵、控制阀门等主要系统组件的工作原理及结构图，回顾了热动力气系统的发展，评述了该系统的使用阶值。     

贮箱内液体重定位运动的动力效应研究

本文研究低重力环境下贮箱内液体重定位运动的动力效应及其影响，概述了模拟低重力环境下液体重定位运动的落塔试验方法，利用小模型落塔试验测定了球型贮箱内液体重定位运动的作用力作用力矩，分析了液体重定位运动的试验相似准则，讨论了液体重定位运动产生的动力交应对航天器的影响以及减小干扰的措施。     

The Protein Crystallisation Diagnostics Facility (PCDF) on Board ESA Columbus Laboratory

Crystals of proteins or macromolecules are at the basis of X-ray crystallography to reveal structural information necessary for the understanding of their likely mode of action. However, the structural resolution is strongly dependent on the crystalline quality, which is known to be related to gravity dependent processes. The facilities and instruments used so far to grow crystals in space have mostly focused on the growing of crystals for detailed post-flight analysis on ground, and less on the understanding of phenomena associated to the crystallisation processes. The Protein Crystallisation Diagnostics Facility (PCDF), developed by Astrium under contract of the European Space Agency (ESA), allows to study with several diagnostics means in situ the crystallisation of macromolecules over long periods in microgravity. In addition, several ground models with PCDF similar capabilities were developed to allow scientists to prepare their experiments. The PCDF is installed in the European Drawer Rack (EDR), on board ESA’s Columbus Laboratory module launched in February 2008 to the International Space Station (ISS) for research in microgravity on protein nucleation and assembling sequences. The PCDF configuration for this first mission accommodates four reactors, using the batch crystallization technique. Individual process control for temperature and concentration will allow several crystallizations of solutions to be performed. Each reactor will be observed by several optical diagnostics, including video microscopy, dynamic light scattering, and Mach–Zehnder interferometry. This paper presents the overall PCDF design and details the different diagnostics allowing the scientific community to use the PCDF in orbit for microgravity research on molecule assemblies grown from solutions.     

Investigation on no-vent filling process of liquid hydrogen tank under microgravity condition

In order to investigate the no-vent filling performance under microgravity, the computational fluid dynamic (CFD) method is introduced to the study, where a model aiming at filling a liquid hydrogen (LH₂) receiver tank is especially established. In this model, the solid and fluid regions are considered together to predict the coupled heat transfer process. The phase change effect during the filling process is also taken into account by embedding a pair of mass and heat transfer models into the CFD software FLUENT, one of which involves liquid flash driven by pressure difference between the fluid saturated pressure and the tank pressure, and the other one indicates and calculates the evaporation–condensation process driven by temperature difference between fluid and its saturated state. This CFD model, verified by experimental data, could accurately simulate the no-vent filling process with good flexibility. Moreover, no-vent filling processes under different gravities are comparatively analyzed and the effects of four factors including inlet configuration, inlet liquid temperature, initial wall temperature and inlet flow rate, are discussed, respectively. Main conclusions could be made as follows: 1) Compared to the situations in normal gravity, the no-vent filling in microgravity experiences a more adequate liquid–vapor mix, which results in a more steady pressure response and better filling performance. 2) Inlet configuration seems to have negligible effect on the no-vent filling performance under microgravity since liquid could easily reach the tank wall and then cause a sufficient fluid-wall contact under any inlet condition. 3) Higher initial tank wall temperature may directly cause a higher pressure rise in the beginning, while this effect on the final pressure is not significant. Sufficient precooling and reasonable inlet liquid subcooled degree are suggested to guarantee the reliability and efficiency of the no-vent fill under microgravity.     

Activation energy asymptotics for methanol droplet extinction in microgravity

An activation energy asymptotic theory for methanol droplet combustion in microgravity is presented by extending earlier models to account for time-dependent water dissolution or evaporation from the liquid droplet. The model predictions for droplet extinction diameter as a function of its initial diameter are shown to compare favorably with experimental results for methanol burning in air.     

Numerical simulation on soot deposition process in laminar ethylene diffusion flames under a microgravity condition

A numerical study on soot deposition in ethylene diffusion flames has been conducted to elucidate the effect of thermophoresis on soot particles under a microgravity environment. Time-dependent reactive-flow Navier-Stokes equations coupled with the modeling of soot formation have been solved. The model was validated by comparing the simulation results with the previous experimental data for a laminar diffusion flame of ethylene (C₂H₄) with enriched oxygen (35% O₂ + 65% N₂) along a solid wall. In particular, the effect of surrounding air velocity as a major calculation parameter has been investigated. Especially, the soot deposition length defined as the transverse travel distance to the wall in the streamwise direction is introduced as a parameter to evaluate the soot deposition tendency on the wall. The calculation result exhibits that there existed an optimal air velocity for the early deposition of soot on the surface, which was in good agreement with the previous experimental results. The reason has been attributed to the balance between the effects of the thermophoretic force and convective motion. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Jae Hyuk Choi received his B.S. and M.S. degrees in Marine System Engineering from Korea Maritime University in 1996 and 2000, respectively. He then went on to receive a Ph.D. degrees from Hokkaido university in 2005. Dr. Choi is currently a BK21 Assistant Professor at the School of Mechanical and Aerospace Engineering at Seoul National University in Seoul, Korea. Dr. Choi’s research interests are in the area of reduction of pollutant emission (Soot and NOx), high temperature combustion, laser diagnostics, alternative fuel and hydrogen production with high temperature electrolysis steam (HTES). Junhong Kim received his B.S., M.S., and Ph. D degrees in Mechanical Engineering from Seoul National University in 1998, 2000, and 2004, respectively. His research interests include lifted flames, edge flames, and numerical simulation. Sang Kyu Choi received his B.S. degree in Mechanical Engineering from Seoul National University in 2004. He is a Ph. D student in the School of Mechanical Engineering, Seoul National University. His research interests include edge flames, oxy-fuel combustion, and numerical simulation. Byoung ho Jeon received his B.S degrees in Mechanical Engineering from kangwon University in 1998, and M.S., Ph. D. degrees in Mechanical Engineering from Hokkaido University in 2002, 2008, respectively. Dr Jeon is working at Korea Aerospace Research Institute from 2007. June. as Gasturbine engine developer. Jeon’s research interests are in the area of reduction of pollutant emission (Soot and Nox), High temperature combustion, combustion system (Furnace, Combine Generation system, IGCC, CTL), and Fire safety in building. Osamu Fujita received his B.S., M.S., and Ph. D. degrees in Mechanical Engineering from Hokkaido University in 1982, 1984, and 1987, respectively. Prof. Fujita is currently a Professor at the division of Mechanical and space Engineering at Hokkaido University in sapporo, Japan. Prof. Fujita’s research interests are in the area of reduction of pollutant emission (Soot and Nox), solid combustion, catalytic combustion, high temperature combustion, alternative fuel and fire safety in space. Suk Ho Chung received his B.S. degree in Mechanical Engineering in 1976 from Seoul National University, and his M.S. and Ph. D. degree in Mechanical Engineering in 1980 and 1983, respectively from Northwestern University. He is a professor since 1984 in the School of Mechanical and Aerospace Engineering, Seoul National University. His research interests cover combustion fundamentals, pollutant formation, and laser diagnostics.     

THE EFFECT OF CONVECTION ON AXISYMMETRIC PARABOLIC DENDRITES

Moving boundary solutions of the Navier Stokes and energy equations are obtained for shape-preserving isothermal paraboloids of revolution by using the Oseen viscous flow approximation. The theoretical results are in good agreement with the precise data of Glicksman et al. on succinonitrilc.

The intensity of thermal convection as indicated by the Grashof number is shown to increase approximately as the inverse of the square of the super-cooling which may have important implications in microgravity experiments.     

微重力条件下熔体中对流过程的数值模拟

微重力条件下生长优质晶体遇到的最大问题是要控制晶体生长的条件，抑制由于重大的减弱而引起的熔体中的热毛细时流。但是，用实验来解决这些问题费用高，周期也长，而且有时完全用实验来模拟也是很困难的。用数值计算方法来模拟微重力条件下熔体中的对流过程是空间晶体生长研究的一个重要的方向，计算结果对控制空间生长晶体和抑制熔体中的对流有指导意义。对微重力条件下熔体中对流发生、发展的过程进行了数值研究。以有限差分法研究了沿上表面为自由表面的水平区域不同边界条件下的熔体中的对流过程。     

Particle conveying under microgravity in a vibrating vessel

This paper presents a numerical study on the conveying of particles in a vibrating vessel under microgravity. Such a vessel is composed of parallel plates with sawtooth wavy surfaces, which are specifically designed to convey particles using simple vibration. The numerical model was validated by good agreement between the simulated and experimental results. Then the effects of key variables, including the vessel geometry, vibration amplitude and frequency and gravity level, were systematically investigated by a series of controlled simulations. The results confirm the optimised design from the previous experiments, and numerically demonstrate that using such a system a steady conveying operation can be achieved under microgravity. The convey rate is positively affected by the vibration amplitude and frequency in a complicated way, which cannot be simply described by the commonly used vibration intensity or velocity amplitude. The gravity level also has a significant effect on the convey rate when it is over 0.001g. The convey rate can be estimated by the product of the average solid fraction and velocity. And the effects of the variables can be better understood through the analyses on these two parameters. Finally, a predictive model is proposed to estimate the convey rate under different operational conditions. The findings are useful for the design of particle conveying techniques for outer space applications.