微重力环境下水平方管内气液两相流动特性的数值研究

基于数值方法,采用流体体积函数模型(volume of fluid,VOF)对10-4g0和g0重力环境下水平方管内空气-水两相流和制冷剂R134a蒸汽-液体两相流进行数值模拟,分别得到泡状流、弹状流、搅混流和环状流4种典型流型,但两种混合物在流型上存在较大差异。通过对数值结果的统计分析,得到两种混合物在不同重力环境下的压降分布。结果显示,微重力下两种混合物的压降均大于常重力环境,且压降都随气、液速度的增大而增大;相同工况下,空气-水的压降大于R134a蒸汽-液体两相流的压降。将得到的压降数值结果与均相流模型、Friedel模型和Chisholm模型依次进行对比。重新根据分液相雷诺数(Reynolds)将流动分为层流区、过渡区和紊流区,并对Chisholm关系式进行了修正。结果显示,修正后的压降模型能较好地预测微重力环境下的气液两相流动压降。根据汽液两相流动特性,分析了发生以上现象的原因。     

Bubble behavior in a horizontal narrow divergent passage (one-dimensional approximate analysis)

This paper investigates the behavior of a bubble which bridges the gap in a cross section of a horizontal narrow divergent passage under Earth's gravity conditions (1 G) analytically. In a narrow passage, inertia forces are known to be small compared with viscous forces. Also, gravity force is not dominant for bubble behavior in a horizontal narrow passage. In this sense, the bubble behavior in the passage is similar to that under microgravity conditions. It is important to understand the bubble behavior in relation to separating gas from a gas–liquid two-phase flow and controlling a gas–liquid interface under microgravity conditions. A one-dimensional momentum equation for the bubble behavior is derived. The equation is arranged as an ordinary differential equation with respect to the upstream interfacial location and is solved. Analytical results are compared with experimental ones. As a result, the effects of gap size, bubble projected area, and divergent angle on bubble behavior are explained qualitatively. © 1999 Scripta Technica, Heat Trans Asian Res, 28(2): 102–114, 1999     

基于分形特征的模拟失重条件下细胞骨架的图像分析

细胞骨架的结构特点决定了不易找到量化细胞骨架图像的特征参数。为了描述模拟失重条件下细胞骨架的形态变化，以评价药物对失重的细胞学效应的防护效果，本文利用双毯法和数盒子数法分别计算细胞骨架微管和微丝图像的分形维数，利用图像的复杂度描述细胞骨架在不同环境中的形态变化。计算结果表明在模拟失重条件下细胞骨架图像的复杂度减弱，加入药物槲皮素后图像的复杂度略有恢复。利用分形维分析细胞骨架在模拟失重条件下图像的纹理变化，其结果表明分形维可以作为特征参数对失重环境中的细胞骨架图像进行定量分析。     

Convection and evaporation of microlayer underneath bubbles under microgravity

The multidimensional heat transfer and fluid flow in the microlayer region below a vapor bubble formed during boiling in microgravity are investigated by numerically solving the Navier–Stokes equations with the energy equation. The flow is driven by Marangoni flow due to the surface tension gradient along the bubble surface that results from the temperature gradient. The model also includes condensation and evaporation at the bubble surface. The flow field and heat transfer are calculated for microlayer thicknesses from 0.01 mm to 10 mm to investigate the effect of microlayer thickness. The results show that the velocities are small and have only a small effect on the temperature distribution as compared to the solution for pure conduction in the liquid. Natural convection is shown to have a negligible effect on heat transfer. For less than ideal evaporative heat transfer at the bubble interface, Marangoni convection caused the heat transfer to increase several percent. The flow in the microlayer is shown to agree with the lubrication analogy only for thin, relatively flat interfaces. © 2000 Scripta Technica, Heat Trans Asian Res, 30(1): 1–10, 2001     

微重力条件对小球藻固碳能力与油脂积累的影响

为了提高微藻的固碳效率和产脂速率,在模拟的微重力条件下,利用CO2培养蛋白核小球藻。实验结果表明:微重力条件和CO2对蛋白核小球藻的生长具有协同促进作用;与普通条件下通入空气培养蛋白核小球藻相比,在微重力条件下通入浓度为10%的CO2培养蛋白核小球藻120 h后,蛋白核小球藻的生物量浓度提高了178%;在普通条件下,蛋白核小球藻的固碳效率为2.64±0.41 mg/(L·h),在微重力条件下,蛋白核小球藻的固碳效率为17.28±0.42 mg/(L·h);在普通条件下通入CO2后,蛋白核小球藻细胞中的不饱和脂肪酸含量升高,而在微重力条件下通入CO2后,蛋白核小球藻细胞中的不饱和脂肪酸含量会下降。     

微重时矩形容器内静液面形状研究

本文由力学平衡方程导出了微重时矩形容器内静液面方程；通过变换，导出了求解静液面形状的迭代公式。计算得出了数值结果；绘出了静液面形状。     

Effect of Gravity on the Macroscopic Advancing Contact Angle of Sessile Drops

A series of experiments were conducted in a reduced gravity (near‐free‐fall) environment (g = 0) and on ground (g = 1) to study the effect of gravity on the advancing contact angles of sessile drops. The reduced net acceleration force was produced by parabolic flights. The ground experiments were conducted for various three‐phase contact‐line advancing rates whereas the reduced gravity experiments were conducted for only one advancing rate due to the short duration of reduced gravity. The experimental results show that for water sessile drops on Teflon‐coated silicon wafers, the advancing contact angle in the reduced gravity environment is less than that of the advancing contact angle in 1g (126°) by about 5° for the same three‐phase contact line advancing rates.     

Fire safety research in microgravity: How to detect smoke and flames you cannot see

Any design requiring the application of technology contains a challenge to achieve a safe design. Manned space flight requires the highest degree of attention to crew safety, thus understanding and recognizing all potential risks involved. An important area of concern is establishing design criteria for a reliable fire detection and suppression system. This has been a main target when designing the European pressurized manned module Columbus Attached Laboratory as part of the international space station. This paper describes experiments performed to investigate the behavior of fires and the fluid dynamics of suppression agents in microgravity by means of parabolic flight maneuvers as an aid for the development of a design of a fire detection and suppression system for the manned Columbus Attached Laboratory.Reprinted fromHazard Prevention: Journal of the System Safety Society, Fourth Quarter, Volume 30, No. 4, 1994, with permission from the author.This paper was presented at the Twelfth International System Safety Society Conference in New Orleans, Louisiana, on July 5 through 10, 1994.