Vortex Flows in the Liquid Layer and Droplets on a Vibrating Flexible Plate

In certain conditions, in the layers and droplets of a liquid on a vibrating rectangular flexible plate, vortex flows are formed simultaneously with the excitation of capillary oscillations on the free surface of the liquid layers and droplets. Capillary oscillations in the form of two-dimensional standing waves form Faraday ripples on the free surface of the liquid layer. On the surface of the vibrating droplets, at the excitation of capillary oscillations a light spot reflected from a spotlight source moves along a trajectory in the form of a Lissajous figure observed with a microscope. When vortex flows visualized with graphite microparticles appear in the layer and droplets of a transparent liquid, the trajectory of the light spot on the layer and droplet surface is a two-dimensional trajectory in the form of an ellipse or a saddle. This indicates that the generation of the vortex flows in a liquid at vibrations is due to capillary oscillations in the orthogonally related directions. In the liquid layer and droplets on the surface of the flexible plate, the vibrations of which are generated by bending vibrations, the vortex flows appear due to the plate vibrations and the capillary oscillations of the surface of a layer or a droplet of the liquid. On the free surface of the liquid, the capillary waves, which are parametrically excited by the plate bending vibrations, are additionally modulated by the same bending vibrations in the transverse direction.     

Model of Film Flow in a Dead-End Conic Capillary

A physical theory of formation and growth of a liquid column in the dead end of a conic capillary submerged in a liquid has been constructed. It has been established that the mechanism of their phenomenon is based on the film flow (stabilized by disjoining pressure) over capillary walls because of the difference of pressures in two liquid columns due to capillary forces. The main qualitative features of the process following from the theory, namely, the constancy of the liquid flow to the vertex with time and the linear dependence of the inverse specific flow on the angle of opening of capillaries, have been confirmed experimentally.     

Study into Correlation between the Ultrasonic Capillary Effect and Sonoluminescence

The correlation between the phenomena of luminescence generation in the cavitation region (sonoluminescence) and increase of the height and velocity of liquid rise in a capillary under the action of ultrasound (ultrasonic capillary effect) has been investigated. It is shown that with small gaps between the capillary and emitter the thresholds of these effects, i.e., minimum values of the amplitude of oscillations at which they originate, virtually coincide. Variation of the parameters which leads to an increase in the intensity of sonoluminescence results in increase of the ultrasonic capillary effect. The results obtained confirm the hypothesis of the cavitation nature of the ultrasonic capillary effect and indicate the possibility of using a capillary as an indicator of activity of acoustic cavitation.     

Minimum concentration of surface-active material required for damping of capillary waves

It is shown that for low concentrations of surface-active and surface-inactive materials dissolved in a liquid, their effect on the behavior of capillary wave motion differs from the case of standard concentrations: the surface-active material does not cause the capillary wave damping, while the surface-inactive material does not destroy the stability of the free surface of the liquid. The presence of an electric charge on the free surface of the liquid weakens the phenomenon. Pis’ma Zh. Tekh. Fiz. 23, 74–79 (March 26, 1997)     

The shape of a liquid surface in a uniformly rotating cylinder in the presence of surface tension

The free-surface shape of a liquid in a uniformly rotating cylinder in the presence of surface tension is determined before and after the onset of dewetting at the bottom of the cylinder. Two scenarios of liquid withdrawal from the bottom are considered, with and without deposition of thin film behind the liquid. The governing non-linear differential equations for the axisymmetric liquid shapes are solved numerically by an iterative procedure similar to that used to determine the equilibrium shape of a liquid drop deposited on a solid substrate. The numerical results presented are for cylinders with comparable radii to the capillary length of liquid in the gravitational or reduced gravitational fields. The capillary effects are particularly pronounced for hydrophobic surfaces, which oppose the rotation-induced lifting of the liquid and intensify dewetting at the bottom surface of the cylinder. The free-surface shape is then analyzed under zero gravity conditions. A closed-form solution is obtained in the rotation range before the onset of dewetting, while an iterative scheme is applied to determine the liquid shape after the onset of dewetting. A variety of shapes, corresponding to different contact angles and speeds of rotation, are calculated and discussed.     

Influences of miscible and immiscible oils on flow characteristics through capillary tube—part I: experimental study

A capillary tube is widely used as an expansion device for small refrigeration cycles. In a practical refrigeration cycle, some amount of refrigeration oil is discharged from a compressor and refrigerant/oil mixture flows through the capillary tube. This study investigated experimentally the influence of mixing of the refrigeration oil with the refrigerant on the flow through the capillary tube. The experiments are carried out with not only a miscible combination of refrigerant and oil but also an immiscible combination. In both cases, the mass flow rate through the capillary tube and temperature and pressure distributions along the tube are measured under several conditions of subcooled degree and oil concentration. In the case of miscible combination, the mass flow rate of refrigerant decreases with increasing the oil concentration because the viscosity of liquid phase increases by the mixing of viscous oil. Even in the case of the immiscible combination, the oil droplet is so small that it mixes homogeneously in the liquid phase in the capillary tube and the refrigerant mass flow rate decreases by the mixing of immiscible oil. There is no significant influence of the oil concentration on the underpressure, which means pressure difference between saturation pressure and flash inception pressure, in both miscible and immiscible combinations.     

Experimental Investigation of a Bubbly Two-Phase Flow in an Open Capillary Channel under Microgravity Conditions

The study of a bubbly laminar two-phase flow in an open capillary channel under microgravity conditions was conducted aboard the sounding rocket, Texus-45. The channel geometry, the liquid (FC-72) and the experimental conditions were chosen based on an analysis for application toward liquid management in space. The channel consists of two parallel plates that were b = 25 mm wide and separated by a distance of a = 10 mm. The flow along the length l = 80 mm is bounded by a free surface on one side and a plate on the opposite side. Bubbles are injected at the inlet of the capillary channel via six capillary tubes. The features of the gas injection were chosen with regard to the required bubble size, the injection frequency, and the gas and liquid flow rates. Different liquid and gas flow rates were tested leading to a volumetric quality ranging between 0.07 and 0.11. The experimental results show the interaction among bubbles and with the liquid free surface.     

Flow Rate Limitation of Steady Convective Dominated Open Capillary Channel Flows Through a Groove

An open capillary channel is a structure that establishes a liquid flow path when the capillary pressure caused by surface tension forces dominates in comparison to the hydrostatic pressure induced by gravitational or residual accelerations. To maintain a steady flow through the channel the capillary pressure of the free surface has to balance the pressure difference between the liquid and the surrounding constant pressure gas phase. Due to convective and viscous momentum transport the pressure along the flow path of the liquid decreases and causes the free surface to bend inwards. The maximum flow rate through the channel is reached when the free surface collapses and gas ingestion occurs near the outlet. This stability limit depends on the geometry of the channel and the properties of the liquid. In this paper we present an experimental setup which is used in the low-gravity environment of the Bremen Drop Tower. Experiments with convective dominated systems have been performed where the flow rate was increased up to the maximum value. In comparison to this we present a one-dimensional theoretical model to determine important characteristics of the flow, such as the free surface shape and the limiting flow rate. Furthermore we present an explanation for the mechanism of flow rate limitation for these flow conditions which is similar to the choking problem for compressible gas flows.     

脉动热管的力学分析

脉动热管是涉及多物理学科、多参数的气液两相流系统,研究和分析微小尺度下脉动热管内部系统的受力是进行脉动热管理论建模和机理分析的基础。作用在脉动热管内液塞上的力有液塞两侧气泡的压力、壁面与液塞间的摩擦剪切力、液塞两端的毛细作用力和液塞重力。以无水乙醇为例计算了各个作用力的大小,发现液塞两侧气泡的压力和液塞两端的毛细作用力是影响液塞脉动的主要因素。     

Ultrasound-modulated twin-fluid atomization of a liquid jet

A resonant liquid capillary wave theory which extends Taylor's dispersion relation to include the sheltering effect of liquid surface inclination caused by air flow is presented. The resulting dispersion curves are compared to new experimental results of how drop-size and size distributions vary with surface tension and air velocity in both airblast and ultrasound-modulated twin-fluid atomization of liquids with a constant kinematic viscosity of 2 cSt. Good agreements between the theoretical predictions of relative growth rates of the capillary waves and the experimental results of drop-size and size distributions led to the conclusion that Taylor-mode breakup of capillary waves plays a very important role in twin-fluid (airblast) atomization of a liquid jet. Thus, the ultrasound-modulated twin-fluid atomization not only verifies the capillary wave mechanism but also provides a means for controlling the drop-size and size distributions in twin-fluid atomization, which has a variety of applications in fuel combustion, spray drying, and spray coating.     

Homogenization modeling of capillary forces in selective laser sintering

We study the initial stage of liquid phase sintering when the particles rearrangement due to densification forces is over. The heterogeneous medium is a mixture of powders, connected by liquid necks. It gives a fluid-structure problem built on a periodic domain, with three phases: an isotropic elastic solid, a newtonian, incompressible, weakly viscous liquid and a barotropic viscous gas. We study this equilibrium under the action of capillary forces on solid-liquid boundary. We penalize the divergence free condition in the liquid and by the energy method, we obtain the homogenized problem satisfied by the macroscopic displacement field in the homogenized medium. The result gets close to a Stokes problem where the capillary forces act as a density of body forces and the viscosity effects vanish.     

建立快速测定空分设备液氧中氧化亚氮的分析方法

介绍一种利用毛细管热导检测器气相色谱法(GC-TCD)测定空分设备液氧中氧化亚氮的检测方法。比较了填充柱和毛细管柱、脉冲放电检测器和热导检测器的优缺点,从生产实际出发,确定选择10m的毛细管PQ柱和热导检测器的搭配,对空分设备旁冷凝器的液氧中氧化亚氮含量进行监控。实际运用情况表明:该方法具有分析准确、过程时间短和稳定性好的优点。     

Design and performance of a universal sheathless capillary electrophoresis to mass spectrometry interface using a split-flow technique

A split-flow capillary electrophoresis electrospray ionization mass spectrometry (CE/ESI-MS) interface is introduced, in which the electrical connection to the CE capillary outlet is achieved by diverting part of the CE buffer out of the capillary through an opening near the capillary outlet. The CE buffer exiting the opening contacts a sheath metal tube which acts as the CE outlet/ESI shared electrode. In cases in which the ESI source uses a metal needle, the voltage contact to the CE buffer is achieved by simply inserting the outlet of the CE capillary, which contains an opening, into the existing ESI needle (thereby greatly simplifying the CE to MS interfacing). As a result of the concentration-sensitive nature of ESI, splitting a small percentage of the CE flow has minimal effect on the sensitivity of detection. In addition, because the liquid is flowing through the opening and out of the capillary, there is no dead volume associated with this interface. Moreover, bubble formation due to redox reactions of water at the electrode does not effect CE/ESI-MS performance, because the actual metal/liquid contact occurs outside of the CE capillary. The sensitivity associated with a sheathless CE/MS interface, the ease of fabrication, universality, and lack of any dead volume make this design a superior CE/ESI-MS interface. The performance of this interface is demonstrated by analyses of a peptide standard and a protein digest using a variety of capillary dimensions.     

Accuracy of the toroidal approximation for the calculus of concave and convex liquid bridges between particles

In situations and processes where finely divided solids are in contact with small amounts of liquid, capillary effects influence the behavior of such systems. If the quantity of liquid is rather limited, it arranges as individual liquid bridges connecting the solid particles just wetting a portion of the solids surface. These bridges develop forces which drive the cohesion and motion of the solid particles, further determining in many times the final structure or even the quality of the material. Since the liquid is not able to fully cover the solid particles like in a proper suspension, this liquid adopts a shape which is determined by the principle of constant mean curvature. A rigorous determination of such a shape, which in turn determines the capillary forces, must be carried out by solving the Young–Laplace equation. Due to the difficulties in such calculation, it was proposed to approximate the meniscus profile by an arc-of-circumference, the so-called toroidal approximation. Here it is quantitatively studied the suitability of such approximation for the most general geometry of liquid bridges, finding that the error of the approximation is below 10% for concave menisci and 30% for convex ones.     

On-column electrochemical reactions accompanying the electrospray process

It is well-established that electrochemical reactions can occur within the capillary of an electrospray (ES) devise coupled to a mass spectrometer. In fact, such reactions must occur to maintain charge balance during the ES process. However, electrochemical reactions occurring distal to the capillary as a result of the high potential applied to the capillary have not been thoroughly investigated. In the present communication, we show that electrochemical processes can occur on a high performance liquid chromatography (HPLC) column coupled to an ES capillary. On-column solvent electrolysis is proposed to generate free radicals, which can subsequently initiate analyte oxidation. Oxidation of steroid sulfates possessing a reactive double bond between C-5 and C-6 is demonstrated. The possibility of similar reactions occurring within peptides possessing a site of unsaturation is also considered.     

Visual Experiments of Bubble Growth and Departure at the Tip of Inclined Capillary Tubes in a Stagnant Liquid

The bubble growth and departure at the tip of inclined glass capillary tubes in stagnant fluid is experimentally investigated by using a high-speed visual system. The visual experiments show that the bubble growth experiences a sphere-like growth stage and the asymmetric growth stage at the tip of an inclined capillary tube. In the asymmetric growth stage, the bubble firstly gets an upward deflection under action of buoyancy force and then the triple contact line of the bubble detaches from the downside of the tube tip and withdraws into the tube. In the period of bubble departure, the neck of the bubble shrinks towards the upside of the tube tip and finally breaks up at the far upper portion of inner surface edge. The incursion of liquid into the tube tip has been detected after the bubble departing from tube tip. It is found that the departure size and the growth cycle period of the bubble as well as the volume of liquid incursion into the tube are decreased with an increase in the inclined angle of the tube. A smaller inner diameter of the inclined capillary tube leads to a smaller bubble departure size and a shorter cycle period of the bubble growth.     

Characterization of the microdialysis junction interface for capillary electrophoresis/microelectrospray ionization mass spectrometry

A capillary electrophoresis/electrospray ionization mass spectrometry (CE/ESI-MS) interface, based on an electric circuit across a microdialysis membrane surrounding a short capillary segment closely connected to the separation capillary terminus, is demonstrated to be sensitive, efficient, and rugged. A microspray type ionization emitter produces a stable electrospray at the low flow rates provided by CE and thus avoids both the need for a makeup liquid flow provided by liquid junction or sheath flow interfaces and the subsequent dilution and reduction in sensitivity. Reproducibility studies and comparisons with CE/UV and the CE/sheath flow interface with ESI-MS are presented. Additionally, postrun acidification via the microdialysis junction interface is demonstrated and shown to be capable of denaturing the holomyoglobin protein noncovalent complex while maintaining separation efficiency.     

Single-walled carbon nanotubes used as stationary phase in GC

Single-walled carbon nanotubes (SWNTs) have high surface area, high adsorption ability, and nanoscale interactions. In this study, capillary columns including SWNTs, ionic liquid (IL), and IL + SWNTs for GC were prepared. The separation results showed that SWNTs possessed a wide selectivity toward alkanes, alcohols, aromatic compounds, and ketones, and a SWNT capillary column was a very useful GC column for the separation of gas samples. Coating the IL stationary phase on the SWNT capillary column, the SWNTs were able to improve chromatographic characteristic of ionic liquid. Comparing the IL coated on three graphite carbon black capillary columns, which were prepared by dynamic coating, static coating, and chemical bonding the Carbopack C with on SWNTs capillary column, the capacity factors were much higher on the SWNT column. The SEM showed that SWNTs could be bonded to the inner surface of capillary tubing, and most of them were linked end-to-end to form a layer of network structure of skeletons resulting in a high surface area, which increased the interactions between stationary phase and analytes. This is the first single-wall carbon nanotubes bonded to the fused-silica capillary tubing. In the first approach, SWNTs assist ionic liquid with enhanced chromatographic characteristic in GC. This work indicates that SWNTs make it possible to extend the application range on the newly prepared chromatographic stationary phases for GC.