Experimental and numerical analysis of the emulsification of oil droplets in water with high frequency focused ultrasound.

Focused high frequency ultrasound emulsification provides significant benefits such as enhanced stability, finer droplets, elevated focal pressure, lowered power usage, minimal surfactant usage and improved dispersion. Hence, in this study, the high frequency focused ultrasound emulsification of oil droplets in water was investigated through experiments and numerical modeling. The effect of transducer power (74-400 W), frequency (1.1 and 3.3 MHz), oil viscosity (10.6-512 mPas), interfacial tension (25-250 mN/m) and initial droplet radius (10-750 µm) on the emulsification process was assessed. In addition, the mechanism of droplet break-up was examined. The experiments showed that the acoustic pressure increased from 9.01 MPa to 26.24 MPa as the power was raised from 74 W to 400 W. At 74 W, the Weber number (We) at the surface and focal zone are 0.5 and 939.8, respectively. However, at 400 W, the We at the transducer surface and focal region reached 2.7 and 6451.8, respectively. Thus, bulb-like and weak catastrophic break up dominates the emulsification at 74 W. The catastrophic break up at 400 W is more vigorous because the ultrasound disruptive stress and We are higher. The time for the catastrophic dispersion of a single droplet at We = 939.8 and We = 6451.8 are 1.01 ms and 0.45 ms, respectively. The numerical model gives reasonable prediction of the trend and magnitude of the experimental acoustic pressure data. The surface and focal pressure amplitudes were estimated with errors of âˆ¼ 6.5% and âˆ¼ 10%, respectively. The predicted Reynolds number (Re) between 74 and 400 W were 8442 and 21364, respectively. The acoustic pressure at the focal region were âˆ¼ 26 MPa and âˆ¼ 69 MPa at frequencies of 1.1 MHz and 3.3 MHz, respectively. Moreover, the acoustic velocities were âˆ¼ 16 m/s and âˆ¼ 42 m/s at 1.1 MHz and 3.3 MHz, respectively. Hence, smaller droplets could be attained at higher frequency excitation under intense catastrophic modes. The Ohnesorge number (Oh) increased from 0.062 to 3.12 with the viscosity between 10.6 mPas and 530 mPas. However, the We remained constant at 856.14 for the studied range. Generally, higher critical We is required for the different breakup stages as the viscosity ratio is elevated. Moreover, the We increased from 25.68 to 1284.22 as the droplet radius was elevated from 15 to 750 µm. Larger droplets allow for higher possibility and intensity of breakup due to diminished viscous and interfacial resistance.

Techno-economic comparative assessment of the ultrasound, electrostatic and microwave supported coalescence of binary water droplets in crude oil.

In this study, comparative assessment of the technical performance, energy usage and economic impact of ultrasound, electrostatics and microwave on the coalescence of binary water droplets in crude oil was conducted. The effect of different oil properties such as crude oil viscosity (10.6-106 mPa s) and interfacial tension (IFT) (20-250 mN/m) on the coalescence time and energy consumption was examined. In addition, operation conditions such as inlet emulsion flow velocity (10-100 mm/s), electric field type, ultrasound frequency and applied voltage amplitude (0-30 kV) were evaluated. The numerical models showed good agreement with experimental findings in the literature. Moreover, the process time of the dewatering process increased with rising inlet flow velocities. The elevation of the coalescence time with velocity can be attributed to the increasing effect of flow disturbance, and the reduction of the emulsion residence time. As regards the IFT, the coalescence time reduced as the IFT was increased. This can be associated with the improved stability of emulsions formed at lowered IFT. As the maximum droplet size is directly proportional to the IFT, lowering the IFT reduces the peak diameter of the droplets that are present in the emulsion. Moreover, the coalescence time followed the order: ultrasound < microwave < electrostatics approaches under varying IFT. The coalescence energy increased from ∼15 J, ∼90 J and ∼25 mJ to ∼61 J, ∼235 J and ∼26 mJ for microwave, electrostatics and ultrasound techniques, respectively, as the viscosity was raised from 10.6 to 106 mPa s. Ultrasound coalescence showed significant energy and economic savings in comparison to microwave and electro-coalescence. Hence, ultrasound coalescence would be a potential method for standalone or integrated demulsification over the two other techniques. However, there are indications that beyond a viscosity of 300 mPa s, the effect of ultrasound becomes weak with significant hindrance to droplet movement and accumulation. This analysis provides fundamental insights on the comparative behavior of the three emulsion separation techniques.

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

In this study, a numerical assessment of the coalescence of binary water droplets in water-in-oil emulsion was conducted. The investigation addressed the effect of various parameters on the acoustic pressure and coalescence time of water droplets in oil phase. These include transducer material, initial droplet diameter (0.05-0.2 in), interfacial tension (0.012-0.082 N/m), dynamic viscosity (10.6-530 mPas), temperature (20-100 °C), US (ultra sound) frequency (26.04-43.53 kHz) and transducer power (2.5-40 W). The materials assessed are lead zirconate titanate (PZT), lithium niobate (LiNbO3), zinc oxide (ZnO), aluminum nitride (AlN), polyvinylidene fluoride (PVDF), and barium titanate (BaTiO3). The numerical simulation of the binary droplet coalescence showed good agreement with experimental data in the literature. The US implementation at a fixed frequency produced enhanced coalescence (t = 5.9-8.5 ms) as compared to gravitational settling (t = 9.8 ms). At different ultrasound (US) frequencies and transducer materials, variation in the acoustic pressure distribution was observed. Possible attenuation of the US waves, and the subsequent inhibitive coalescence effect under various US frequencies and viscosities, were discussed. Moreover, the results showed that the coalescence time reduced across the range of interfacial tensions which was considered. This reduction can be attributed to the fact that lower interfacial tension produces emulsions which are relatively more stable. Hence, at lower interface tension between the water and crude oil, there was more resistance to the coalescence of the water droplets due to their improved emulsion stability. The increment of the Weber number at higher droplet sizes leads to a delay in the recovery of the droplet to spherical forms after their starting deformation. These findings provide significant insights that could aid further developments in demulsification of crude oil emulsions under varying US and emulsion properties.

Reusable Sensor for Strontium Sulfate Scale Monitoring in Seawater.

The onset of scaling in oil pipelines can halt or drastically reduce oil production, causing huge financial losses and delays. Current methods used to monitor scaling can take weeks, while the scaling process only takes few hours. The proposed sensor is designed for online monitoring of strontium ions concentration in seawater as an early scaling indicator. The sensor operates in the GHz range by probing the shift in the resonance frequency due to changes in the ionic concentrations of the medium. The results show selective sensitivity to changes in the strontium ions concentration even in the presence of many other ions found in seawater. The measured sensitivity is found to be stable and linear with a detection level of better than 0.08% (0.042 mol/L) of strontium ions in seawater. This work demonstrates a robust GHz sensor for strontium sulfate scale monitoring and early detection, which could be used in the oil industry to prevent huge production losses. These results could also be extended further to target the monitoring of other ions in different industrial sectors.

Assessing the Stability of Inkjet-Printed Carbon Nanotube for Brine Sensing Applications.

In hostile environments, sensing is critical for many industries such as chemical and oil/gas. Within this industry, the deposition of scales or minerals on various infrastructure components (e.g., pipelines) forms a reliability hazard that needs to be monitored. Therefore, the approach adopted in this study to tackle this issue relies on the use of real-time sensing of specific ions in brine, the natural trigger for ions deposition. In order to do so, electrochemical sensors based on carbon nanotubes (CNTs) are developed, taking advantage of their unique properties facilitated by different synthesis and fabrication methods. One of these promising synthesis methods is inkjet printing of CNT films since in general, it has exceptional benefits over other approaches that are used to print CNTs. Furthermore, it does not need the use templates. In addition, it is a very fast technique with consistent printing results for many applications along with very low cost on various shapes/formfactors. As these sensors are exposed to a hostile environment (chemical, temperature, etc.), the stability of the CNT films is of great importance. In this study, a comprehensive investigation of the stability of CNT surfaces upon exposure to elements is presented. Accordingly, the several impacts of this interaction on physical properties of the surfaces as a function of interaction time and brine chemical composition are assessed. Moreover, the approach used for investigating the impact of this exposure involves the following: surface electrical resistance change using four probe measurements; surface roughness/topography using Atomic Force Microscopy (AFM) along Scanning Electron Microscopy (SEM); quality of CNT through Raman spectroscopy and wettability using the sessile drop method. The sensing capabilities of the devices are investigated by looking at the sensing selectivity of target ions, resetting capabilities, and sensing sensitivity manifested in the electrical resistance change. Consequently, our results indicate that while inkjet films are very promising sensor material, the fabrication and long term stability require further optimization of the films along with the process to make them meet reliability and lifetime requirements in the oil/gas hostile operational environments.