The Role of Capillarity in Two-Phase Flow through Porous Media

When determining experimentally relative permeability and capillary pressure as a function of saturation, a self-consistent system of macroscopic equations, that includes Leverett's equation for capillary pressure, is required. In this technical note, such a system of equations, together with the conditions under which the equations apply, is formulated. With the aid of this system of equations, it is shown that, at the inlet boundary of a vertically oriented porous medium, static conditions pertain, and that potentials, because of the definition of potential, are equal in magnitude to pressures. Consequently, Leverett's equation is valid at the inlet boundary of the porous medium, provided cocurrent flow, or gravity-driven, countercurrent flow is taking place, and provided the porous medium is homogeneous. Moreover, it is demonstrated that Leverett's equation is valid for flow along the length of a vertically oriented porous medium, provided cocurrent flow, or gravity-driven, countercurrent flow is taking place, and provided the porous medium is homogeneous and there are no hydrodynamic effects. However, Leverett's equation is invalid for horizontal, steady-state, forced, countercurrent flow. When such flow is taking place, it is the sum of the pressures, and not the difference in pressures, which is related to capillary pressure.     

Discontinuous Galerkin method for solving the black‐oil problem in porous media

We introduce a new algorithm for solving the three‐component three‐phase flow problem in two‐dimensional and three‐dimensional heterogeneous media. The oil and gas components can be found in the liquid and vapor phases, whereas the aqueous phase is only composed of water component. The numerical scheme employs a sequential implicit formulation discretized with discontinuous finite elements. Capillarity and gravity effects are included. The method is shown to be accurate and robust for several test problems. It has been carefully designed so that calculation of appearance and disappearance of phases does not require additional steps.     

Numerical prediction of breakup mode of contracting gas filament in liquid

The breaking up of gas filament in liquid is important in many industrial and scientific applications. In this study, a transient axisymmetric model with the level set method is built up to examine the dynamics of a contracting gas filament, and to determine the effects of the aspect ratio, Ohnesorge (Oh) number, and viscosity ratio on its breakup mode. The filament undergoes no break, middle break, or end-pinching modes with increasing aspect ratio at either a low or a high Oh number, and one critical initial aspect ratio is observed for each Oh number. The fate of the filament is determined by the interaction of capillary waves on its surface, and can be predicted accurately by using the one-dimensional wave superposition method. The decreasing viscosity ratio of liquid over gas reduces the critical initial aspect ratio for the fate transition between the no break and breakup modes, and this effect is reduced at a low viscosity ratio. These findings may be helpful in fabricating gas bubbles and their breakup suppression.     

Some possibilities of an analysis of complex samples by a mass spectrometry with a sample pretreatment by an offline coupled preparative capillary isotachophoresis

This work deals with an analysis of biologically important compounds in complex matrices using preparative isotachophoresis (pITP) in column coupling configuration as a sample pretreatment technique followed by a direct infusion mass spectrometry with nano‐electrospray ionization (DI‐nESI‐MS). Busereline was chosen as a model analyte, and urine was chosen as an example of complex matrix. In pITP experiments, sodium cation (10 mmol/L concentration) was used as a leading ion and β‐alanine as terminating ion (20 mmol/L concentration). The fractions, obtained by pITP pre‐separation with the assistance of the mixture of discrete spacers, were finally analyzed by DI‐nESI‐MS. It was shown that pITP performed before DI‐nESI‐MS analysis can significantly simplify complex matrix, and, due to its concentration power, pITP can consequently decrease the concentration limit of detection. The concentration of buserelin in the urine samples analyzed by pITP‐DI‐nESI‐MS was 10 μg/L (reflecting at a 8.10^?9 mol/L concentration) in our work but from the ion intensities obtained in MS as well as MS/MS analyses, it is clear that this concentration level could be several orders of magnitude lower for reliable detection and identification of buserelin in urine analyzed using pITP with DI‐nESI‐MS detection.     

Analysis of Alaskan crude oils by glass capillary gas chromatography/mass spectrometry

Glass capillary gas chromatography/mass spectrometry is used to profile Alaskan crude oil for purposes of origin verification. Alaskan oil, sampled at Valdez, Alaska, and transshipped to the U.S. East Coast, is compared with 21 samples of foreign crude oil using GC/MS techniques in which original data is reconstructed at selected parent and fragment ions to generate a series of chromatographic profiles. Comparison of selected profiles and compositional parameters derived from peak ratios allows distinction of Alaskan oil from many foreign crudes and may be applied to the examination of crude mixtures.     

整体柱的制备方法及其应用

整体柱具有渗透性好、制备简单、无需塞了制作等优点,从而避免了由塞了所引起的问题,已引起人们越来越多的关注。本文对整体柱的制备方法、结构表征及其应用作一评述。     

Simultaneous determination of iodide and iodate in seawater by transient isotachophoresis-capillary zone electrophoresis with artificial seawater as the background electrolyte

We developed capillary zone electrophoresis with transient isotachophoresis (ITP) as an on-line concentration procedure for simultaneous determination of iodide and iodate in seawater. The effective mobility of iodide was decreased by addition of 20 mM cetyltrimethylammonium chloride to an artificial seawater background electrolyte so that transient ITP functioned for both iodide and iodate. Limits of detection for iodide and iodate were 4.0 and 5.0 microg/l (as iodine) at a signal-to-noise ratio of 3. Values of the relative standard deviation of peak area, peak height, and migration times for iodide and iodate were 2.9, 1.3, 1.0 and 2.3, 2.1, 1.0%, respectively. The proposed method was applied to simultaneous determination of iodide and iodate in seawater collected at a pond at our university.     

Resolution of sulphur-containing amino acids by chiral phase gas chromatography

Summary Methyl esters of the pentafluoropropionyl-amino acid derivatives of the tetrafunctional, sulphur-bridged, stereoisomeric lanthionines, cystathionines and -methyl-lanthionines were resolved on glass capillaries coated with the chiral stationary phase N-propionyl-L-valine-N-tert-butylamide-polysiloxane (Chirasil-Val) within 35min. Interestingly, L-cystathionine elutes before its D-enantiomer in contrast to the usual order of emergence on an L-phase. The method was applied to the polypeptide antibiotic nisin, which contains mesolanthionine and 2S,3S,6R-3-methyl-lanthionine.N-Pentafluoropropionyl-S-alkylthiocysteine methyl esters (R=methyl, ethyl, n- and iso-propyl, n- and sec-butyl, n-octyl, neo-pentyl, cyclohexyl-, benzyl-, tolyl-) were separated on Chirasil-Val within 30min. The identity of all derivatives was shown by combined gas chromatography-mass spectrometry.     

Gas chromatography of plasma amino acids using a wide bore column: Comparison with packed and capillary columns

A procedure is described in which a wide bore glass capillary column is used as an alternative to the more traditional packed column in the analysis of amino acid levels in plasma. The coefficients of variation for all amino acids (with the exception of aspartic acid) were better than 11% with recoveries ranging from 81% to 122%. The data are compared with the corresponding results obtained using a packed column and show significant differences (p < 0.005) between values for glycine, serine, isoleucine, proline, methionine, aspartic acid, phenylalanine, and lysine. A similar comparison between results from the wide bore and the fused-silica open tubular (FSOT) column shows better agreement. Adjustment of chromatographic conditions for the wide bore analysis yields results in good agreement with those from FSOT analysis but which still differe significantly from the backed column data.     

高效毛细管电泳法测定酱油中山梨酸的含量

对山梨酸在１０ｍｍｏｌ／Ｌ硼砂和１０ｍｍｏｌ／Ｌ十二烷基硫酸钠溶液中的毛细管电泳行为进行了研究，在２５４ｎｍ检测波长下，考察了载体溶液各组分对分离的影响，得到了最佳分离条件，峰面积相对标准偏差４．１％。山梨酸在０．０２～１ｍｍｏｌ／Ｌ浓度范围内有良好的线性，将此法用于酱油中山梨酸的测定，取得令人满意的结果。