Oil Droplet Capture by Tunicates

Wastewater generation is a growing concern in the preliminary treatment of heavy crude oil and tar sand. The separation of fine oil droplets from water by flotation is a critical process in the production of bitumen from tar sand. The flow structure from a high-resolution simulation of a single air macrobubble (>3 mm diameter) rising through water in the presence of a very dilute dispersion of mono-sized oil microdroplets (30 μm) under quiescent conditions is presented. A combined model of computational fluid dynamics (CFD), a volume of fluid (VOF) multiphase approach, and the discrete phase method (DPM) was developed to simulate bubble dynamics, the trajectories of the dispersed oil droplet, and the interaction between the air bubble and the oil droplet in quiescent water. The CFD–VOF–DPM combined model reproduced the interacting dynamics of the bubble and oil droplets in water at the bubble–droplet scale. With an extremely large diameter ratio between the bubble and the dispersed oil droplet, this model clearly demonstrated that the dominant mechanism for the interaction was the hydrodynamic capture of oil droplets in the wake of a rising air macrobubble. The entrainment of the oil droplets into the wake of the rising bubbles was strongly influenced by the bubble’s shape.

Downhole oil-water separation is one of the key technologies of single-well injection and production, and how to enhance the separation performance of downhole oil-water separator is significant to improve the applicability of single-well injection-production technology. In order to improve the purification precision of downhole oil-water, a hydraulic coalescer is proposed based on the principle of swirl separation. The effects of structural parameters on oil droplet coalescence characteristics and coalescence performance are studied by combining Euler-Euler model with population balance model (PBM). The effects of structural parameters on particle size distribution, pressure drop and coalescence performance of oil droplets in the coalescer were simulated and analyzed. Results show that the hydraulic coalescer presents a good coalescence performance of oil droplets in downhole produced fluid. The lengths of cone tube and outlet tube, radius of coalescence inner core have effect on oil droplets size distribution and coalescence performance. When the length of cone and outlet is 500 mm and 80 mm respectively, diameter of coalescence core is 10 mm, the optimal coalescence performance is obtained. When the size distribution of inlet oil droplets is 25–55 μm, the size distribution of oil droplets after coalescence can be increased to 150–300 μm. The length of conical tube influences on the pressure loss of coalescer more significant than other does. This study will refer to improve the accuracy of downhole oil-water separation and innovative design of downhole separator.KeywordsOil dropletStructural parametersPopulation balance modelCoalescence performanceSimulation method

Characteristics of Oil Droplets Stabilized by Mineral Particles: Effects of Oil Type and Temperature

We have numerically demonstrated micro droplet migrations by photothermal manipulation, in order to investigate the driving force and accompanying flows. We focus on an oil (oleic acid) droplet in water that provides a positive temperature dependence of interfacial tension. The present direct numerical simulation employs the volume-of-fluid method and the continuum-surface-force method with consideration of temperature dependency. The driving velocity and force magnitude, which we measured quantitatively, agree with experimental and theoretical data. We have found that the dominant driving force exerted on the microdroplet is the interface normal force, i.e., the Laplace pressure, on a curved interface rather than the tangential force. The tangential component directly triggers the Marangoni convection; however, the induced flows inside the droplet are opposite between the cases of “an oil droplet in water” and “a water droplet in oil”. This may be caused by the large difference between the viscosities of water and oil.

Numerical assessment of ultrasound supported coalescence of water droplets in crude oil

In microfluidics, water droplets are often used as independent biochemical microreactor units, enabling the implementation of massively parallel screening assays where only a few of the reacting water droplets yield a positive result. However, sampling the product of these few successful reactions is an unsolved challenge. One possible solution is to use acoustic tweezers, which are lab-free, easily miniaturized, and biocompatible manipulation tools, and existing acoustic tweezers manipulating particles or cells, and water droplet manipulation in oil with an acoustic tweezer is absent. The first challenge in attempting to recover a few water droplets from a large batch is the selective manipulation of water droplets in an oil system. In this paper, we trap and manipulate single water droplets in oil using integrated single-beam (focused beam/vortex beam) acoustic tweezers for the first time. We find that water droplets with a diameter smaller than half a wavelength are trapped by acoustic vortices, while larger ones are better captured by focused acoustic beams. It is the first step to extract the target water droplet microreactors (positive ones) in an oil system and analyze their content. Compared to previous techniques, such as fluorescence-activated cell sorting (FACS), our technique is sparse, meaning that the sampling time is proportional to the number of droplets required and very insensitive to the total number of microreactors, making it well suited for large-scale screening assays.

Probing the coalescence mechanism of water droplet and Oil/Water interface in demulsification process under DC electric field

Electrophoretic mobility does not always reflect the charge on an oil droplet

When studying the entrainment of oil under breaking waves, accurately measuring the size distribution of oil droplets is crucial as it determines their rise velocity, which in turn controls vertical distribution and resurfacing, and impacts horizontal transport due to current shear. Droplet size is also important for dissolution of soluble oil components, as well as biodegradation. In climate models, air-sea exchange is an important parameter, which is also related to bubble size distributions, concentrations and depth distribution of air bubbles under breaking waves in the ocean.   Traditional image processing techniques for measuring droplet and bubble sizes rely on classifying and measuring the size of each droplet in an image separately, which can lead to an artificially large size distribution due to overlapping bubbles. To address this issue, we employed Mask-R-CNN for image segmentation, allowing us to classify all instances in an image simultaneously. This approach enables us to more accurately predict the size distribution of bubbles and droplets, as overlapping bubbles are more easily classified as separate entities. Additionally, this method allows us to work with more chaotic images near the surface of breaking waves without sacrificing precision. We present our results from this approach, which provide a more accurate understanding of the size distribution of air bubbles and oil droplets under breaking waves.

In order to improve the inadequacy of the current research on oil droplet size distribution in aero-engine bearing chamber, the influence of oil droplet size distribution with the oil droplets coalescence and breakup is analyzed by using the computational fluid dynamics-population balance model (CFD-PBM). The Euler–Euler equation and population balance equation are solved in Fluent software. The distribution of the gas phase velocity field and the volume fraction of different oil droplet diameter at different time are obtained in the bearing chamber. Then, the influence of different initial oil droplet diameter, air, and oil mass flow on oil droplet size distribution is discussed. The result of numerical analysis is compared with the experiment in the literature to verify the feasibility and validity. The main results provide the following conclusions. At the initial stage, the coalescence of oil droplets plays a dominant role. Then, the breakup of larger diameter oil droplet appears. Finally, the oil droplet size distribution tends to be stable. The coalescence and breakup of oil droplet increases with the initial diameter of oil droplet and the air mass flow increasing, and the oil droplet size distribution changes significantly. With the oil mass flow increasing, the coalescence and breakup of oil droplet has little change and the variation of oil droplet size distribution is not obvious.

Acoustic manipulation of particles in microchannels has recently gained much attention. Ultrasonic standing wave (USW) separation of oil droplets or particles is an established technology for microscale applications. Acoustofluidic devices are normally operated at optimized conditions, namely, resonant frequency, to minimize power consumption. It has been recently shown that symmetry breaking is needed to obtain efficient conditions for acoustic particle trapping. In this work, we study the acoustophoretic behavior of monodisperse oil droplets (silicone oil and hexadecane) in water in the microfluidic chip operating at a non-resonant frequency and an off-center placement of the transducer. Finite element-based computer simulations are further performed to investigate the influence of these conditions on the acoustic pressure distribution and oil trapping behavior. Via investigating the Gor'kov potential, we obtained an overlap between the trapping patterns obtained in experiments and simulations. We demonstrate that an off-center placement of the transducer and driving the transducer at a non-resonant frequency can still lead to predictable behavior of particles in acoustofluidics. This is relevant to applications in which the theoretical resonant frequency cannot be achieved, e.g., manipulation of biological matter within living tissues.

Detecting and quantifying extremely low concentrations of oil from the environment have broad applications in oil spill monitoring in ocean and coastal areas as well as in oil leakage monitoring on land. Currently available methods for low-concentration oil detection are bulky or costly with limited sensitivities. Thus they are difficult to be used as portable and field-deployable detectors in the case of oil spills or for monitoring the long-term effects of dispersed oil on marine and coastal ecosystems. Here, we present a low-concentration oil droplet trapping and detection microfluidic system based on the acoustophoresis phenomenon where oil droplets in water having a negative acoustic contrast factor move towards acoustic pressure anti-nodes. By trapping oil droplets from water samples flowing through a microfluidic channel, even very low concentrations of oil droplets can be concentrated to a detectable level for further analyses, which is a significant improvement over currently available oil detection systems. Oil droplets in water were successfully trapped and accumulated in a circular acoustophoretic trapping chamber of the microfluidic device and detected using a custom-built compact fluorescent detector based on the natural fluorescence of the trapped crude oil droplets. After the on-line detection, crude oil droplets released from the trapping chamber were successfully separated into a collection outlet by acoustophoretic force for further off-chip analyses. The developed microfluidic system provides a new way of trapping, detecting, and separating low-concentration crude oil from environmental water samples and holds promise as a low-cost field-deployable oil detector with extremely high sensitivity. The microfluidic system and operation principle are expected to be utilized in a wide range of applications where separating, concentrating, and detecting small particles having a negative acoustic contrast factor are required.

Chemical design of self-propelled Janus droplets

The bounce behavior of a freely rising oil droplet in water under the horizontal wall constraint

An experimental study on the motion of water droplets in oil under ultrasonic irradiation