微流量调节阀在液体饱和蒸气压测定实验中的应用

在液体饱和蒸气压测定实验装置中,引入微流量调节阀对缓冲储气罐进行改造,使导入系统的空气流量精确可控,解决了调压时需反复调节、操控难、空气倒灌等问题,缩短了实验时间。使用该装置以静态法测定了乙醇的饱和蒸气压,在实验教学中获得了良好的效果。     

外压与凝聚态物质饱和蒸气压关系的讨论

应用外压与饱和蒸气压的关系公式,推导了范霍夫公式和开尔文公式。温度一定时,平液面的饱和蒸气压只会大于或等于真空密闭系统中纯物质气液平衡时的饱和蒸气压。毛细管的凹液面还会出现比平液面的饱和蒸气压小的情况。该关系公式称为"凝聚相表面的压力与饱和蒸气压的关系公式"更为合理。     

电流变阻尼器的抗冲击性能研究

从理论和试验两个方面研究了所设计的电流变阻尼器在大冲击下的抗冲击性能,分析了电流变液性能与阻尼器结构参数对抗冲击性能的影响.认为采用高性能的电流变液体及改变结构参数,都可以使电流变阻尼器的高速缓冲性能提高.电流变液流速对电流变液的屈服应力影响显著,其值随流速的增加按指数规律减小.从定性、定量两个方面分析了电流变阻尼器作为阻尼器效果不明显的原因为:由电流变效应引起的阻尼力在整个液压阻力中所占比例太小,不能通过改变电压来使液压阻力具有很大的调节可控范围.     

完全不互溶双液系的蒸气压*

对完全不互溶双液系的饱和蒸气压进行了实验研究与理论讨论,认为完全不互溶双液系的平衡蒸气压随两组分相互溶解度减小而趋于但总是小于两纯组分的饱和蒸气压之和;当完全不互溶两液相一起静置时,上层液体能有效但不能完全阻止下层液体的挥发,这种阻止作用源于缓慢溶解、扩散和挥发这些动力学过程;提出了阻止下层液体挥发的方法,即用与之完全不互溶且密度小的液体来覆盖,并且2种液体充满容器,阴凉处密闭静置保存。     

化学实验中的气体压强问题

压强是一个物理概念,化学实验中的喷泉实验、气密性检验、排液量气、倒吸实验等均与气体压强有关。对中学化学实验中的气压问题做了归纳与整合,并以相应的高考题例证。     

测定阿佛加德罗常数的简易方法

一、实验原理一定质量(WMg)的金属镁与过量的稀硫酸反应,置换出的氢气的体积为VH2。量气管内所收集的氢气是被水蒸气所饱和的,故量气管内的气压P(等于大气压力),是氢气的分压PH2与实验温度t℃时饱和水蒸气的分压PH2O的总和。     

锥形色谱分离系统及其分离纯化的方法

本发明公开了一种锥形色谱分离系统及其分离纯化方法,其中分离纯化的方法包括:将加压装置与加样装置相连,利用加压装置进行压力调节,以便压实填料;将待分离样品通过加样装置加入到分离装置中,同时利用加压装置,使待分离样品迅速、均匀的通过出样孔喷出,形成雾化样液,并快速进入填料床面;待分离样品吸附完成后,将洗脱液供给至储液装置中进行样品洗脱处理。由此,可以根据实验需要适时选择加样装置和加压装置,实现均匀、快速的加样,并对储液装置进行压力调节,操作简便,保障分离纯化的实验效果以及实验操作的安全性。     

平衡管清洗及装液方法的改进

针对在测定液体饱和蒸气压实验中使用的平衡管(又称为等压计)较难清洗和装液的问题,经过实践摸索,设计了一个清洗平衡管及装液的实验装置。通过用循环水泵给系统抽真空、用调节阀控制各个分支的真空度、在平衡管内使用细径导管导流等手段控制平衡管内液体的流动,达到清洗和装液的目的。该实验装置易于搭建,操作方法易于掌握。使用该方法的操作者能够独立、快速地完成清洗平衡管和装入待测液,从而为开展与液体饱和蒸气压测定相关的实验教学和科研工作创造了更好的实验条件。     

氢气在混合溶剂丙酮-水中的溶解度

本文报导一种能准确测定气体在混合溶剂中溶解度并能同时测定溶剂的饱和蒸气压的实验装置, 在20～40 ℃的温度范围内, 分别测定了氢气在丙酮、水和混合溶剂丙酮-水中的溶解度, 及其相应的蒸气压。     

部分互溶体系的盐效应研究(I)

用实验测定了NaCl、KCl、KBr三种盐在正丁醇-水、丁酮-水共8个三元部分互溶体系的液液平衡数据, 采用加盐饱和密度法进行平衡两相组成的分析, 并用Chen模型进行了关联。     

纯液体饱和蒸气压测定实验中新型平衡管的应用

通过设计新型结构的平衡管,解决了液体饱和蒸气压的测定实验中存在的平衡管加样及清洗困难、气体倒灌、蒸气不纯等问题,一次加样就可完成饱和蒸气压测定工作,操作便利,效率提高,所得实验数据准确性好。     

Gas Holdups of Small and Large Bubbles in a Large-scale Bubble Column with Elevated Pressure

Gas holdups of large bubbles and small bubbles were measured by means of dynamic gas disengagement approach in the pressured bubble column with a diameter of 0. 3 m and a height of 6.6 m. The effects of su-perficial gas velocity, liquid surface tension, liquid viscosity and system pressure on gas holdups of small bub-bles and large bubbles were investigated. The holdup of large bubbles increases and the holdup of small bub-bles decreases with an increase of liquid viscosity. Meanwhile, the holdup of large bubbles decreases with in-creasing the system pressure. A correlation for the holdup of small bubbles was obtained from the experimen-tal data.     

Pressure dependence of liquid epoxy resin impregnation through polyester non-woven fabric in vacuum

The mechanism for liquid epoxy resin impregnation through polyester nonwoven fabric, sandwiched between two circular glass plates in atmospheric pressure, has been studied by the Kozeny-Carman equation improved by the introduction of the theoretical calculated capillary force and the gas leakage parameter for the void formation in the impregnating area. Impregnating velocity increases with reduced gas pressure. Experimental data on the vacuum impregnation were analyzed by the improved Kozeny-Carman equation by using wettability under measurements of the ascending heights due to liquid epoxy resin impregnation in a vacuum. The gas leakage quantity, obtained from the gas leakage parameter, is related to the gas pressure at the starting point of the impregnation. Voids for most of the impregnation stage disappear with passing impregnating time, 120 minutes as well as breaking the vacuum in the chamber.     

热致相分离聚偏氟乙烯膜接触器法高压吸收CO2过程及数学模拟

研究了膜接触器法高压吸收混合气中CO2的过程,考察水作为吸收剂时,操作压力、气体和吸收剂流量对聚偏氟乙烯(PVDF)中空纤维膜脱除CO2效果的影响.通过物理传质模型得出气相、膜相和液相的传质方程式,构建了二维数学模型,并结合边界层条件和多物理场耦合分析软件(COMSOL MULTIPHYSICS)对膜接触器法高压物理吸收CO2的过程进行了模拟预测.结果表明,吸收过程中膜的润湿情况显著影响CO2传质效果;在数学模型中引入润湿率,可以较准确预测CO2的物理吸收效果.     

Pressure drop of slug flow in microchannels with increasing void fraction: experiment and modeling

Pressure drop in a gas-liquid slug flow through a long microchannel of rectangular cross-section was investigated. Pressure measurements in a lengthy (～0.8 m) microchannel determined the pressure gradient to be constant in a flow where gas bubbles progressively expanded and the flow velocity increased due to a significant pressure drop. Most of the earlier studies of slug flow in microchannels considered systems where the expansion of the gas bubbles was negligible in the channel. In contrast, we investigated systems where the volume of the gas phase increased significantly due to a large pressure drop (up to 1811 kPa) along the channel. This expansion of the gas phase led to a significant increase in the void fraction, causing considerable flow acceleration. The pressure drop in the microchannel was studied for three gas-liquid systems; water-nitrogen, dodecane-nitrogen, and pentadecane-nitrogen. Inside the microchannel, local pressure was measured using a series of embedded membranes acting as pressure sensors. Our investigation of the pressure drop showed a linear trend over a wide range of void fractions and flow conditions in the two-phase flow. The lengths and the velocities of the liquid slugs and the gas bubbles were also studied along the microchannel by employing a video imaging technique. Furthermore, a model describing the gas-liquid slug flow in a long microchannel was developed to calculate the pressure drop under conditions similar to the experiments. An excellent agreement between the developed model and the experimental data was obtained.     

High Pressure Liquid Chromatography of Selected Sulfur Compounds

Abstract

High pressure liquid chromatography was used to separate and determine quantitatively the following groups of sulfur compounds: thiols, sulfides, disulfides, sulfones, isothiocyanates, thioamides, and thioureas. Amperometric and UV detectors were compared; for thiols, thioureas, isothiocyanates, and thioamides, the former was generally more sensitive. With the exception of alkyl and cycloalkyl sulfides, the liquid chromatographic method can be used for the analysis of the investigated sulfur compounds below the ppm range. The method developed was compared to gas chromatography with flame photometric detection. The latter was found to be superior for the analysis of alkyl and cycloalkyl thiols, sulfides and disulfides of molecular weight below 200, whereas the former was more suitable for the analysis of aromatic thiols, sulfides and disulfides, as well as thioamides, isothiocyanates, and thioureas. Both methods were equivalent for the analysis of aromatic sulfones.     

Pressure dependence of the vapor-liquid-liquid phase behavior in ternary mixtures consisting of n-alkanes, n-perfluoroalkanes, and carbon dioxide

Expansion of an organic solvent by an inert gas can be used to tune the solvent's liquid density, solubility strength, and transport properties. In particular, gas expansion can be used to induce miscibility at low temperatures for solvent combinations that are biphasic at standard pressure. Configurational-bias Monte Carlo simulations in the Gibbs ensemble were carried out to investigate the vapor-liquid-liquid equilibria and microscopic structures for two ternary systems: n-decane/n-perfluorohexane/CO2 and n-hexane/n-perfluorodecane/CO2. These simulations employed the united-atom version of the transferable potential for phase equilibria (TraPPE-UA) force field. Initial simulations for binary mixtures of n-alkanes and n-perfluoroalkanes showed that special mixing parameters are required for the unlike interactions of CHx and CFy pseudoatoms to yield satisfactory results. The calculated upper critical solution pressures for the ternary mixtures at a temperature of 298 K are in excellent agreement with the available experimental data and predictions using the SAFT-VR (statistical associating fluid theory of variable range) equation of state. The simulations yield asymmetric compositions for the coexisting liquid phases and different degrees of microheterogeneity as measured by local mole fraction enhancements.     

Pressure Effects in Adsorption Systems

A study of the occurrence of large pressure and flow transients when a strongly adsorbed gas is fed to a column which is initially loaded with a lightly adsorbed gas is presented here. Under certain conditions, these transients can cause premature breakthrough and change the shape of the breakthrough curve. This will result in improper estimation of adsorption parameters by the dynamic column loading method and lower apparent adsorption capacity in a full scale unit. A data acquisition system was used to record the pressure and flow transients. An isothermal PDE model developed to study these transients agreed reasonably well with the nonisothermal experimental results. The PDE model predicts that pressure and flow transients will occur during step and pulse~tests conducted to obtain adsorption and mass transfer parameters by the chromatographic method. For instance, lower adsorption capacity will be realized during step tests due to lowering in column pressure. Oscillations were observed when columns are connected in series. The PDE model also predicts these oscillations. Simulations indicate that the extent of oscillations is dependent on the dead volume between columns.     

Dual buffer gases for ion manipulation in a miniature ion trap mass spectrometer with a discontinuous atmospheric pressure interface

The discontinuous atmospheric pressure interface (DAPI) has been developed to allow a direct transfer of ions from atmosphere into an ion trap mass spectrometer with minimum pumping capability. Air is introduced into the trap with ions and used as a buffer gas for the ion trap operation. In this study, a method of introducing helium as a second buffer gas was developed for a miniature mass spectrometer using a dual DAPI configuration. The buffer gas effects on the performance of a linear ion trap (LIT) with hyperbolic electrodes were characterized for ion isolation, fragmentation and a mass-selective instability scan. Significant improvement was obtained with helium for resolutions of mass analysis and ion isolation, while moderate advantage was gained with air for collision-induced dissociation. The buffer gas can be switched between air and helium for different steps within a single scan, which allows further optimization of the instrument performance for tandem mass spectrometry.     

Anomalous Capillary Pressure, Stress, and Stability of Solids-Coated Bubbles

A two-dimensional theoretical model for solids-coated, or "armored," bubbles shows how the armor can support a liquid-vapor interface of reduced or reversed curvature between the particles, giving the bubble zero or even negative capillary pressure. The inward capillary force pulling the particles into the center of the bubble are balanced by large contact forces between the particles in the armor. Thus the bubble is stabilized against dissolution of gas into surrounding liquid, which otherwise would rapidly collapse the bubble. The stresses between particles in such cases are large and could drive sintering of the particles into a rigid framework. Earlier work on solids-coated bubbles assumed that solids can freely enter or leave the bubble surface as the bubble shrinks or expands. In such a case, armored bubbles would not be stable to gas dissolution into surrounding liquid. A new free-energy analysis, however, suggests that a shrunken bubble would not spontaneously expel a solid particle from its armor to relieve stress and allow the bubble to shrink further. Implications and limitations of the theory are discussed. Copyright 1999 Academic Press.