A combined experimental and computational fluid dynamics analysis of the dynamics of drop formation

This article presents a complementary experimental and computational investigation of the effect of viscosity and flowrate on the dynamics of drop formation in the dripping mode. In contrast to previous studies, numerical simulations are performed with two popular commercial computational fluid dynamics (CFD) packages, CFX and FLOW-3D, both of which employ the volume of fluid (VOF) method. Comparison with previously published experimental and computational data and new experimental results reported here highlight the capabilities and limitations of the aforementioned packages

Interfacial tension of aqueous and hydrocarbon systems in the presence of carbon dioxide at elevated pressures and temperatures

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Application of axisymmeric profile analysis for measuring surface tension at harmonic surface oscillations

Тензіометрія аналізу профілю як розвиток стандартного аналізу осесиметричної форми краплі використана для вимірювання поверхневого натягу рідин методом форм крапель і бульбашок різних конфігурацій. Алгоритм швидкого пошуку застосований для розрахунку ортогональної відстані між точками експериментального профілю і теоретичним профілем. Встановлена прийнятна стабільність результатів в діапазоні до 60% зміни об'єму краплі або бульбашки. За результатами вимірювань оцінені параметри вязкоеластичності.Тензиометрия анализа профиля как развитие стандартного анализа осесимметричной формы капли использована для измерения поверхностного натяжения житкостей методом форм капель и пузырьков различных конфигураций. Алгоритм быстрого поиска применен для расчета ортогонального расстояния между точками экспериментального профиля и теоретическим профилем. Установлена приемлемая стабильность результатов в диапазоне до 60% изменения объема капли или пузырька. По результатам измерений оценены параметры вязкоэластичности.The profile analysis tensiometry as a development of the standard analysis of axissymmetric drop shape was used for measuring the surface tension of drops and bubbles of different configurations. A “Quick Search” algorithm was applied to calculate the orthogonal distance between the experimental profile points and the theoretical profile. An acceptable stability of the results was established in a range for up to 60% of drop/bubble volume changes. The parameters of the surface visco-elasticity were estimated on the basis of these surface tension measurements

National Educators' Workshop: Update 1988. Standard Experiments in Engineering Materials Science and Technology

Presented here is a collection of experiments presented and demonstrated at the National Educators' Workshop: Update 88, held May 10 to 12, 1988 at the National Institute of Standards and Technology (NIST), Gaithersberg, Maryland. The experiments related to the nature and properties of engineering materials and provided information to assist in teaching about materials in the education community

Interfacial Tension Measurement near Wax Appearance Temperature

This report includes the whole summary of the study of interfacial tension (IFT) measurement near wax appearance temperature (WAT) which is the title of final year project. The scope of this study is to measure three different parameters which are wax appearance temperature (WAT), density and interfacial tension (IFT) using three different equipment which are micro differential scanning calorimeter, anton paar density meter and spinning drop tensiometer. In the literature review, it will explain about the interfacial tension effect on the temperature and other parameters, the oil-water flow behavior, wax appearance temperature and how to determine it by the past research which is by using various methods. Besides, the problem statement of this study is to experimentally study the IFT trending near wax appearance temperature which is related to the problem statement which is lacking of experimental data of interfacial tension measurement near wax appearance temperature. Through the methodology, this experiment will have three experiments need to be carried out which are: determining the wax appearance temperature of three different crude oils, density of oil samples, and interfacial tension of three different crude oils near wax appearance temperature. All the equipment used for this experiments is available in UTP laboratory and do not need the outside facilities. The results that acquired from this experiment is still reasonable and the accuracy is high enough even for wax appearance temperature experiment which just repeated two times. From the result, it is shown that, interfacial tension is directly proportional to the temperature near WAT. While the density is inversely proportional to the temperature. The IFT trending that acquired is different to each other which might be due to the different composition of the crude oils. Recommendation that can be provided here is, to carry out the experiments with more trials, repeat it using different field or region waxy crude oil and use another equipment to carry out all three experiments. As a conclusion, IFT trending every waxy crude oil is different to each other and it tends to decrease as temperature decrease

The role of microparticles on the shape and surface tension of static bubbles

HYPOTHESIS: Surface tension is a critical parameter in bubbles and foams, yet it is difficult to assess when microparticles are attached at the interface. By considering the interaction force between an air-liquid interface and microparticles, modified equations for sessile bubble tensiometry can be derived to determine the surface tension and shape of static microparticle-laden bubbles. EXPERIMENTS: A modified sessile bubble method, in which the forces between microparticles and the air-liquid interface are considered, was developed and used to analyse the surface tension of bubbles fully coated by a monolayer of silica microparticles of different sizes. The results are compared to those obtained using classical sessile bubble tensiometry. The new method is also used to investigate the contours of particle-laden bubbles of varying particle radius and contact angle. FINDINGS: While the classical sessile bubble method overestimates the surface tension, results obtained using the modified sessile bubble method show that the surface tension of static microparticle-laden bubbles remains the same as that of uncoated bubbles, with no dependency on the particle size. The discrepancy is due to the fact that microparticles attached to the air-liquid interface deform a bubble in a similar way that changes in surface tension do for uncoated bubbles

Liquid-liquid Dispersion in Batch and In-line Rotor-Stator Mixers

This two-part dissertation investigates the behavior of batch and in-line rotor-stator mixers separately. In the first study, water was dispersed into viscous oil using a batch Silverson L4R rotor-stator mixer. The flow regime was determined by reference to published Power number data and by qualitative differences in drop size data. Drop breakup in laminar flow was analyzed by comparison to published single drop breakup experiments in idealized flow fields. The breakup mechanism in laminar flow was similar to that for simple shear flow and equal to about twice the nominal shear rate in the rotor-stator gap. Drop breakup in turbulent flow followed a mechanistic correlation for mean drop size for drops less than the Kolmogorov microscale, but still large enough that both inertial and viscous effects were manifest. Surfactants decreased drop size with Marangoni effects observed near the CMC for laminar, but not for turbulent flow. Below phase fractions of 0.05, d32 increased in a log-linear fashion with phase fraction for all conditions tested including: laminar and turbulent flow, presence of surfactant, and hydrophobically treated high-shear surfaces. The significant effect of phase fraction was caused by the flow structure being locally laminar near the drops, and was permitted by sufficiently low fluid viscosities which promoted film drainage. Above phase fractions of 0.1, drop sizes plateaued. This was attributed to decreasing coalescence rate and efficiency, along with increasing breakup. In the second study, the power consumption of an IKA 2000/4 in-line pilot scale rotor-stator mixer was measured with a purpose-built torque meter. The power spent by the mixer on pumping was insignificant compared to viscous dissipation. A constant power number was obtained for turbulent flow using constant power per stage with an empirically determined effective diameter for each generator type. For conditions where mean drop size was close to equilibrium, as determined by flowrate independence, previously reported mean drop size data were calculated using the well-known inertial subrange scaling law along with the power draw measurements of the present study. The maximum local energy dissipation rate was found to be nine times the average energy dissipation rat

Kinetic friction of nonwetting drops

Numerous engineering applications have been proposed to exploit the load-carrying and non-contact nature of noncoalescing and nonwetting systems. One such application is a lab-on-a-chip , or LOC, in which liquid samples would be delivered from point-to-point by sliding over a film of air without requiring either the large driving forces required to pump liquid through a microchannel or liquid-solid contact that could lead to sample-to-sample contamination. Due to the axisymmetry of the flow fields in both the lubricating gas and droplet associated with a stationary nonwetting droplet, such a situation has a vanishing coefficient of static friction. However, once motion is imparted, droplet deformation requires that a force be applied to sustain such motion. The program of research in this dissertation focuses on investigating the lubrication force between a drop of silicone oil and a moving unwetted substrate due to the presence of a gas lubricating film driven by a rotating disk. The frictional (or lubrication) force was measured using an optical-lever technique as a function of: (1) linear velocity of the moving solid; (2) relative displacement of the drop toward the solid; (3) drop volume; and (4) viscosity. The data reveal an increase in magnitude of the measured force with either increasing relative squeezing of the drop against the glass or increasing speed of the rotating disk. Contrary to initial expectations, no pattern could be isolated regarding drop volume or viscosity of the oil. The experimental data collected will serve to validate numerical work as further models are developed.Ph.D.Committee Chair: Neitzel, G. Paul; Committee Member: Allen, Mark G.; Committee Member: Degertekin, F. Levent; Committee Member: Schatz, Michael; Committee Member: Smith, Marc K

Coalescence of contaminated water drops at an oil/water interface: Influence of micro-particles

The effect of micro-particles and interface aging on coalescence of millimetre-sized water drops with an oil/water interface is studied over long times. The system is not pure and interface contamination grows with time, resulting in a slow but continuous decrease of interfacial tension over time (from 35 to 10 mN/m), which is measured in situ using an original technique. Without added micro-particles, coalescence times are randomly distributed and uncorrelated to drop diameter or interfacial tension. In presence of 10 !m size hollow glass particles at the oil/water interface, coalescence times become more reproducible and show a clear dependence upon drop diameter and interface aging. Results are consistent with a classical drainage model assuming that the critical thickness at which interstitial film ruptures scales as the micro-particle diameter, a result that tends to validate the bridging scenario. Interestingly, the film retraction speed during the coalescence process does not follow theoretical predictions in a planar geometry. High-speed imaging of the retracting film reveals that the hole rim is bending upward while retracting, resulting in a strong slowdown of retraction speed. This is caused by the difference of interfacial tension between oil/drop freshly formed interfaces and the aged oil/water interface