Interfacial stability of binary mixtures evaporating at reduced pressure

1983 ◽  
Vol 126 ◽  
pp. 491-506 ◽  
Author(s):  
Arijit Bose ◽  
Harvey J. Palmer
Keyword(s):  
Mass Transfer ◽  
Surface Tension ◽  
Surface Concentration ◽  
Interfacial Stability ◽  
Concentration Effects ◽  
Reduced Pressure ◽  
The Difference ◽  
Hydrodynamic Stability Theory ◽  
Evaporative Flux ◽  
The Stability

When a liquid evaporates under vacuum, its free surface is potentially unstable to local variations in evaporative flux, surface depressions being produced by the recoil force of the departing vapour and sustained convection in the liquid being driven by the shearing action of the vapour on the distorted liquid surface. For a binary mixture, local variations in evaporative flux may be produced by fluctuations in both surface concentration and temperature. With the aid of linear hydrodynamic-stability theory, this paper examines the extents to which key mass-transfer properties affect the interfacial stability of the system. The mass-transfer aspects that distinguish this problem from its heat-transfer analogue centre on the dependence of relative volatility on temperature and composition as well as the importance of the bulk-flow term in Fick's law. Results indicate that the stability criteria for interfacial convection are extremely sensitive to the difference in volatility between the two components, that the destabilizing effects of surface concentration and temperature on evaporative flux are additive in determining stability limits, and that for certain operating pressures spontaneous convection can only be induced by adverse concentration gradients. Attention is limited to low-surface-tension mixtures for which there are no concentration effects on surface tension (Marangoni instability).

Theoretical investigation of the interfacial stability of inviscid fluids in motion, considering surface tension

1972 ◽  
Vol 54 (1) ◽  
pp. 129-141 ◽  
Author(s):  
Jan Berghmans
Keyword(s):  
Surface Tension ◽  
Analytical Study ◽  
Minimum Free Energy ◽  
Gas Jet ◽  
Interfacial Stability ◽  
Viscous Effects ◽  
Inertia Effects ◽  
Inviscid Fluids ◽  
The Stability

The present work is an analytical study of the stability of interfaces between fluids in motion, special attention being given to the role of surface tension without consideration of viscous effects. A variational approach based upon the principle of minimum free energy, which was first formulated for stagnant fluids, is applied to fluids in motion. This generalization is possible if viscous and inertia effects are unimportant as far as stability is concerned. One stability problem is studied in detail: a gas jet impinging on a free liquid. The analytical results obtained by this variational technique lie within the range of accuracy (15%) of the experimental results for this gas-jet problem. The method is very general and therefore can be applied to quite a number of interface stability problems.

Theory of Heat/Mass Transfer Additives in Absorption Chillers

1999 ◽  
Author(s):  
S. Kulankara ◽  
S. Verma ◽  
K. E. Herold
Keyword(s):  
Mass Transfer ◽  
Surface Tension ◽  
Surface Concentration ◽  
Secondary Flows ◽  
Primary Role ◽  
Absorption Chillers ◽  
Surfactant Additive ◽  
Primary Variable ◽  
Surfactant Theory

Abstract A new theory is presented, termed the vapor surfactant theory, which explains the heat and mass transfer enhancement mechanism of additives in absorption chillers. The vapor surfactant theory holds that the enhancement additives are surfactants delivered to the surface of the solution film from the vapor and that they produce enhancement by generating intense secondary flows on the film. The secondary flows, driven by surface tension gradients (Marangoni convection), augment the transfer process by providing mixing of the film. The primary variable in the enhancement is the surface concentration distribution of the surfactant additive since the surface tension gradients arise due to non-uniformities in the surface concentration. The vapor surfactant theory is found to explain all observations from several different types of experiments. The new theory is a significant departure from past theories in its emphasis on the primary role of the vapor in the process.

Surface Tension Driven Film Flow due to Condensation With a Vapor Borne Surfactant

2000 ◽  
Author(s):  
R. Qiao ◽  
Z. Yuan ◽  
K. E. Herold
Keyword(s):  
Mass Transfer ◽  
Surface Tension ◽  
Heat And Mass Transfer ◽  
Liquid Surface ◽  
Surface Concentration ◽  
Marangoni Flow ◽  
Absorption Chillers ◽  
Mass Transfer Processes ◽  
Surfactant Transport ◽  
Bottom Side

Abstract In absorption chillers, it is well known that the presence of small amounts of alcohol can enhance the absorber heat and mass transfer significantly. Similar enhancement is also observed in the condenser. Among the theories to explain such phenomena, the recently described Vapor Surfactant theory provides the most comprehensive explanation of the available data. According to this theory, the surfactant arrives at the liquid surface primarily from the vapor. As the water vapor flows toward eventual absorption/condensation, it carries the vapor borne surfactant toward the surface. Once the surfactant arrives at the surface, it tends to concentrate there due to its low solubility and low diffusivity in the liquid as well as the natural affinity of a surfactant for the surface. Non-uniform surface concentration of the surfactant leads to surface tension forces in the liquid surface layer that drive the surface flows often observed. These Marangoni flows are what enhance the heat and mass transfer processes. Although it was often theorized that Marangoni flow plays a role in enhancement, the important role of the vapor has not been well understood. A number of previous attempts have been made to compute Marangoni flow but all such attempts have assumed that the surfactant transport in the liquid is the key. This paper presents calculations of liquid film flows driven by the surfactant as it arrives at the surface from the vapor. This completely new model involves several very interesting features. A two-dimension numerical simulation of such a flow is reported here. The geometry is a thin film (3mm × 10cm) of liquid water with a small patch of cooling centered on the bottom side. The upper surface is exposed to steam+surfactant vapor so that condensation will occur. The model computes the surface concentration of surfactant and relates that to the surface tension. Calculations show that the condensation rate is much higher when Marangoni convection is occurring, even if the surfactant concentration in the vapor is very small (120ppm). This is in accordance with observations in absorption chillers. The result helps to clarify understanding of surfactant-induced enhancement of heat and mass transfer in absorption chillers.

scholarly journals The rheological properties of cream liqueurs and their changes in the transportation process

2019 ◽  
Vol 21 (91) ◽  
pp. 149-156
Author(s):  
T. V. Bozhko ◽  
R. S. Donchevska ◽  
R. P. Romanenko
Keyword(s):  
Surface Tension ◽  
Rheological Properties ◽  
Kinematic Viscosity ◽  
Control Sample ◽  
Statistical Error ◽  
Test Substance ◽  
Colloidal System ◽  
Colloidal Systems ◽  
The Difference ◽  
The Stability

In order to determine the stability of colloidal systems of cream liqueurs with cycloractate and egg yolks, their rheological properties after production and during transportation, which was simulated through centrifugation and shaking, study, had been studied. Kinematic viscosity was determined by viscosimetric method using a graduated glass unit and a “Universal Computer Measuring Instrument” manufactured by “ITM Ltd.”, Kharkiv, Ukraine. The coefficient of surface tension was investigated by the method of detachment of the ring from the surface of the test substance, and the density – by the method of hydrostatic weighing. Storage of bottled glass bottles with a capacity of 0.35 l of dessert emulsion cream liqueurs took place in the warehouse at a temperature from +10 to + 250 С and a relative humidity of no more than 85%. Quality indicators in developed beverages were determined at 18, 36, 54, 72, 90 and 108 day. Dynamic viscosity of the sample of dessert emulsion cream liqueur “Healing Source” was 2394.1 MPa · s, cream liqueur “Health” – 2219.7 MPa · s, control sample “Dalkowski Advocaat Starotoruński” – 1949.99 MPa · s. It has been established that the kinematic viscosity and density of developed cream liqueurs are higher by 19.4 ... 21.8% compared with the control sample. For cocktails preparation it is expedient to use a dessert emulsion cream liqueur "Healing Source", the difference of the coefficient of surface tension of which with the control sample lies within the limits of statistical error it is determined. It is noted that in the process of centrifugation, cream liqueurs demonstrate a slight change in rheological properties. The smallest changes in density are noted for emulsion cream liqueur «Healing Source», the largest – for “Health”, due to the peculiarities of their prescription composition. The influence of “shaking effect” on the density of dessert emulsion cream liqueurs was determined. The biggest difference in density after shaking up to 10 s had the cream-liqueur “Health”, after 10s of shaking – the cream-liqueur “Steppe beauty”. The most stable structure of the colloidal system of the cream-liqueur “Healing Source” was the stability difference with the control sample lies within the statistical error.

scholarly journals Electrohydrodynamic Interfacial Stability Conditions in the Presence of Heat and Mass Transfer and Oblique Electric Fields

1999 ◽  
Vol 54 (8-9) ◽  
pp. 470-476
Author(s):  
Mohamed Fahmy El-Sayed
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Electric Field ◽  
Heat And Mass Transfer ◽  
Electric Fields ◽  
Stability Criterion ◽  
Dielectric Constants ◽  
Interfacial Stability ◽  
Mass And Heat Transfer ◽  
The Stability

A novel mathematical formulation to deal with interfacial stability problems of the Kelvin-Helmholtz type with heat and mass transfer in the presence of oblique electric fields is presented. The perturbed system is composed of two homogeneous, inviscid, incompressible, dielectric, and streaming fluids sep-arated by a horizontal interface, and bounded by two rigid planes. The effect of a phase transition on the instability is considered, and the linear dispersion relations are obtained and discussed. It is found that the electric field has a major effect and can be chosen to stabilize or destabilize the flow. For Ray-leigh-Taylor instability problems of a liquid-vapor system it is found that the effect of mass and heat transfer enhances the stability of the system when the vapor is hotter than the liquid, although the clas-sical stability criterion is still valid. For Kelvin-Helmholtz instability problems, however, the classical stability criterion is found to be substantially modified due to the effects of the electric field, mass and heat transfer. A new stability condition relating the magnitude and orientation of the electric field and the dielectric constants is obtained. Oblique electric fields are found to have stabilizing effects which are reduced by the normal components of the electric fields. The effects of orientation of the electric fields and fluid depths on the stability configuration are also discussed.

Use of a Lyophilized Reference Plasma to Compare Coagulation Test Procedures

1975 ◽  
Vol 34 (02) ◽  
pp. 426-444 ◽  
Author(s):  
J Kahan ◽  
I Nohén
Keyword(s):  
Oral Anticoagulant Therapy ◽  
Repeated Measurements ◽  
Test Procedures ◽  
Coagulation Activity ◽  
Close Relationship ◽  
Measured Activity ◽  
Test Materials ◽  
The Difference ◽  
The Stability ◽  
The One

SummaryIn 4 collaborative trials, involving a varying number of hospital laboratories in the Stockholm area, the coagulation activity of different test materials was estimated with the one-stage prothrombin tests routinely used in the laboratories, viz. Normotest, Simplastin-A and Thrombotest. The test materials included different batches of a lyophilized reference plasma, deep-frozen specimens of diluted and undiluted normal plasmas, and fresh and deep-frozen specimens from patients on long-term oral anticoagulant therapy.Although a close relationship was found between different methods, Simplastin-A gave consistently lower values than Normotest, the difference being proportional to the estimated activity. The discrepancy was of about the same magnitude on all the test materials, and was probably due to a divergence between the manufacturers’ procedures used to set “normal percentage activity”, as well as to a varying ratio of measured activity to plasma concentration. The extent of discrepancy may vary with the batch-to-batch variation of thromboplastin reagents.The close agreement between results obtained on different test materials suggests that the investigated reference plasma could be used to calibrate the examined thromboplastin reagents, and to compare the degree of hypocoagulability estimated by the examined PIVKA-insensitive thromboplastin reagents.The assigned coagulation activity of different batches of the reference plasma agreed closely with experimentally obtained values. The stability of supplied batches was satisfactory as judged from the reproducibility of repeated measurements. The variability of test procedures was approximately the same on different test materials.

Analysis and calculation of the process of low-pressure reverse osmosis during recycling of hygienic water

2019 ◽  
pp. 28-36
Author(s):  
Leonid S. Bobe ◽  
Nikolay A. Salnikov
Keyword(s):  
Mass Transfer ◽  
Reverse Osmosis ◽  
Life Support ◽  
Space Station ◽  
Low Pressure ◽  
Operating Pressure ◽  
Life Support System ◽  
Cleaning Agent ◽  
The Difference ◽  
Pressure Channel

Analysis and calculation have been conducted of the process of low-pressure reverse osmosis in the membrane apparatus of the system for recycling hygiene water for the space station. The paper describes the physics of the reverse osmosis treatment and determines the motive force of the process, which is the difference of effective pressures (operating pressure minus osmotic pressure) in the solution near the surface of the membrane and in the purified water. It is demonstrated that the membrane scrubbing action is accompanied by diffusion outflow of the cleaning agent components away from the membrane. The mass transfer coefficient and the difference of concentrations (and, accordingly, the difference of osmotic pressures) in the boundary layer of the pressure channel can be determined using an extended analogy between mass transfer and heat transfer. A procedure has been proposed and proven in an experiment for calculating the throughput of a reverse osmosis apparatus purifying the hygiene water obtained through the use of a cleaning agent used in sanitation and housekeeping procedures on Earth. Key words: life support system, hygiene water, water processing, low-pressure reverse osmosis, space station.

In the stability of paints and varnishes for protective and decorative wood finish

2016 ◽  
Author(s):  
Ю.И. Цой
Keyword(s):  
Organic Solvents ◽  
Evaluation Criteria ◽  
Ternary Systems ◽  
Solubility Parameters ◽  
Formaldehyde Resin ◽  
Film Forming ◽  
The Difference ◽  
Molecular Forces ◽  
The Stability ◽  
Thermodynamic Interaction

Задача получения однородного состава ЛКМ сводится к правильному выбору пленкообразователей и соответствующих растворителей и, в случае необходимости, разбавителей и добавок. На основе положений теории растворимости была проведена оценка совместимости компонентов и стабильности таких систем. Критериями оценки были приняты параметры растворимости и термодинамического взаимодействия. Исследовали совместимость алкидных лаков с аминоформальдегидными смолами в бутаноле, и результаты этих исследований представлены в треугольной фазовой диаграмме. Для оценки совместимости смол по результатам расчета параметров термодинамического взаимодействия были построены спинодали для тройных систем. Как показывает анализ результатов проведенных исследований, даже при большой разности ?? = |?12 – ?13| = 0,2 наблюдается небольшая область несовместимости. С уменьшением разности ?? область несовместимости сужается. При ?23 > ?с область несовместимости расширяется как для ? = 0,2, так и для ?? = 0,1 и ?? = 0. Таким образом, для таких систем на совместимость компонентов, в первую очередь, влияет их взаимодействие между собой – чем оно больше, тем лучше они совместимы. Проведенные исследования показали, что парциальные параметры растворимости, учитывающие природу когезионных сил, более объективно характеризуют растворимость пленкообразующих смол в органических растворителях, чем их общий параметр растворимости. Растворимость пленкообразующих алкидных и этерифицированных аминоформальдегидных смол в органических растворителях обусловлена термодинамическим взаимодействием молекулярных сил различной природы. Стабильность смеси алкидной и этерифицированной аминоформальдегидной смолы в бутаноле обусловлена в большей степени термодинамическим взаимодействием молекулярных сил; при этом степень бутанолизации меламиноформальдегидной смолы оказывает наибольшее влияние на стабильность cистемы. Проведенные исследования по стабильности лакокрасочных смесей из различных пленкообразующих смол на основе рассмотренных критериев оценки могут быть использованы для совершенствования технологии защитно-декоративной отделки древесины. The problem of obtaining a homogeneous composition of the coatings is reduced to the proper selection of film-forming agents, and diluent and, if appropriate, diluents and additives. On the basis of the theory of solubility, we have carried out the assessment of the compatibility of the components and stability of such systems. The evaluation criteria were adopted the parameters of the solubility and thermodynamic interaction. Researched the compatibility with alkyd varnishes aminoformaldehyde resin in butanol, and the results of these studies are presented in the triangular phase diagram. To evaluate the compatibility of the resins according to the results of calculation of thermodynamic parameters of interaction were built spinodal for ternary systems. As the analysis of the results of the studies, even when the difference ??|?12 – ?13| = 0,2 there is a small area of incompatibility. With the decrease of the difference ? ? region incompatibility narrows. When ?23> ?с region incompatibility extends to ?? = 0,2, and for ?? = 0.1 and ?? = 0. Thus, for such systems, compatibility of components, primarily, affects their interaction with each other – the further away it is, the better they are compatible. Studies have shown that the partial solubility parameters, which take into account the nature of cohesive forces, more objectively characterize the solubility of film-forming resins in organic solvents than their total solubility parameter. The solubility and film-forming aminoformaldehyde esterified alkyd resins in organic solvents due to thermodynamic interaction of molecular forces of different nature. Тhe stability of the mixture and aminoformaldehyde esterified alkyd resin in butanol is generated largely by thermodynamic forces of molecular interaction; the degree of butanolate melamine-formaldehyde resin has the greatest effect on the stability of the system. Conducted research on the stability of the paint mixtures of various film-forming resins on the basis of the evaluation criteria can be used to improve the technology of protective and decorative wood finish.

Possible application of approximate models for calculation of selectivity of consecutive reactions under the effect of mass transfer

1982 ◽  
Vol 47 (5) ◽  
pp. 1301-1309 ◽  
Author(s):  
František Kaštánek ◽  
Marie Fialová
Keyword(s):  
Mass Transfer ◽  
Numerical Method ◽  
Analytical Method ◽  
Approximate Analytical Method ◽  
Approximate Models ◽  
Consecutive Reactions ◽  
The Difference

The possibility of use of approximate models for calculation of selectivity of consecutive reactions is critically analysed. Simple empirical criteria are proposed which enable safer application of approximate analytical reactions. A more universal modification has been formulated by use of which the difference of selectivity calculated by the exact numerical method and by the approximate analytical method is at maximum 12%.

Stability and mutual impact of perception of parental pressure and infants' social support – A study based on the difference between employment status and household income

2021 ◽  
pp. 002072092199705
Author(s):  
Yong Wang
Keyword(s):  
Household Income ◽  
Employment Status ◽  
Working Mothers ◽  
Social Research ◽  
Research Report ◽  
Parental Pressure ◽  
Income Levels ◽  
Significant Difference ◽  
The Difference ◽  
The Stability

The purpose of this study is to explore the stability and interaction between parental pressure and social research report, as well as the role of employment status and family income levels in this process. This study used a special study on Korean children (PSKC) 2–4 waves. Use t-test, correlation and autoregressive cross-delay modeling to analyze the data. The main findings of this study are: First, over time, parental pressure and mother’s social research report are consistent. Secondly, the pressure of motherhood and childcare has an obvious lagging effect on upbringing, and vice versa. Third, there is no significant difference between working mothers and non-working mothers in terms of the stability of working parents' pressure, social research report and social research report for children's pressure channels. However, parental pressure can only predict the social research report of working mothers. Fourth, there is no significant difference between the stability and interaction of these two structures in household income levels. In short, the results show that, over time, parental pressure is consistent with mother’s social research report. The results also show that there is a significant cross-lag effect between the mothers’ perceptions of mutual pressure analysis. In the process from parental pressure to social research report, I found the difference between working and non-working mothers. The advantage of this study is that the expected longitudinal design was adopted during infancy and the priority between the two structures can be considered. The results of this study can be used as a source of intervention plans to help parents withstand severe parenting pressure and lack of social research report.

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