Nabil Esmail

Flow Enhancement of Medium-Viscosity Crude Oil

Abstract This study investigated the different alternatives to enhance the flowability of crude oil with medium viscosity. These alternatives include the addition of water into crude oil to form water-in-oil emulsion, the addition of light petroleum product, the addition of flow improver, and a preheating technique. Temperature range of 10–50°C, water concentration range of 0–50% by volume, flow improver concentration range of 0–5000 ppm, and kerosene concentration range of 0–50% by volume were investigated in the flowability enhancement study of crude oil with medium viscosity. The flowability enhancement in terms of viscosity reduction was investigated using RheoStress RS100 from Haake. A cone–plate sensor was used with a cone angle of °4, cone diameter of 35 mm, and 0.137-mm gap at the cone tip. The addition of kerosene to crude oil improves the flowability much better than any other investigated technique.

Shear driven droplet shedding and coalescence on a superhydrophobic surface

The interest on shedding and coalescence of sessile droplets arises from the importance of these phenomena in various scientific problems and industrial applications such as ice formation on wind turbine blades, power lines, nacelles, and aircraft wings. It is shown recently that one of the ways to reduce the probability of ice accretion on industrial components is using superhydrophobic coatings due to their low adhesion to water droplets. In this study, a combined experimental and numerical approach is used to investigate droplet shedding and coalescence phenomena under the influence of air shear flow on a superhydrophobic surface. Droplets with a size of 2 mm are subjected to various air speeds ranging from 5 to 90 m/s. A numerical simulation based on the Volume of Fluid method coupled with the Large Eddy Simulation turbulent model is carried out in conjunction with the validating experiments to shed more light on the coalescence of droplets and detachment phenomena through a detailed analysis of the aerodynamics forces and velocity vectors on the droplet and the streamlines around it. The results indicate a contrast in the mechanism of two-droplet coalescence and subsequent detachment with those related to the case of a single droplet shedding. At lower speeds, the two droplets coalesce by attracting each other with successive rebounds of the merged droplet on the substrate, while at higher speeds, the detachment occurs almost instantly after coalescence, with a detachment time decreasing exponentially with the air speed. It is shown that coalescence phenomenon assists droplet detachment from the superhydrophobic substrate at lower air speeds.

Modeling of the Onset of Gas Entrainment Through a Finite-Side Branch

A theoretical investigation has been conducted for the prediction of the critical height at the onset of gas entrainment during single discharge from a stratified, two-phase region through a side branch with a finite diameter. Two different models have been developed, a simplified point-sink model and a three-dimensional finite-branch model. The two models are based on a new criterion for the onset of gas entrainment

Shear-driven droplet coalescence and rivulet formation

Icing on aerodynamic surfaces occurs due to the accumulation of rain droplets when the surrounding temperature is below the freezing temperature. It is well known that icing phenomenon alters the aircraft aerodynamic forces and may cause serious damage. Therefore, studying water droplet behavior, such as shedding and coalescence serves as the primary step which can lead to understanding the fundamental physics of aircraft icing. Hence, in this study an experimental approach is used to investigate the shear-driven droplet shedding and coalescence on a hydrophilic substrate which can serve as the building block for the formation of rivulets.

The onset of gas pull-through during dual discharge from a stratified two-phase region: Theoretical analysis

A theoretical analysis for the onset of gas pull-through (entrainment) during discharge from a stratified two-phase region through two vertically aligned side branches has been developed in this paper. Initially, a simplified point-sink model was developed, which was then followed by the acquisition of a more accurate finite-branch model. The prediction of the critical height at the onset of gas entrainment was found to be a function of the corresponding Froude number of each branch (Fr1 and Fr2), as well as the vertical distance between the centerlines of the two branches (L/d). The predicted values of the critical height were found to be consistent with the corresponding experimental data for different values of Fr1, Fr2 and L/d. From the basis of the present models, it was found that by increasing the flow through the lower branch, the critical height increases for all values of Fr1 and L/d. Furthermore, by increasing the vertical distance between the two branches, the effect of the lower branch on the...

Shear Driven Rivulet Dynamics on Surfaces With Various Wettabilities

Ice formation leads to significant decrease of aircraft performance and possible disasters. When rain droplets accumulate on aircraft wings, they form narrow films of water known as rivulets. Due to air shear effects, rivulets generate runback flow on the airfoil, enhancing ice formation. In this paper we report the results of an experimental study of the dynamics of narrow water films i.e. rivulets under the effect of various air shear speeds and different surface morphologies ranging from hydrophilic to superhydrophobic. Understanding the dynamics of rivulets is necessary in solving the ice formation problems on airfoils.Copyright

Simulation of complex liquids in micropump

Abstract Complex liquids can be encountered in many applications of microdevices. In the present study, the performance of microscrew pump using complex liquid is investigated numerically. The microscrew pump operation depends on the surface sweep forces. It consists of a screw placed inside a microchannel. When the screw rotates, a net force is transferred to the fluid due to differential pressure on the depth of the thread and pressure gradient along the screw axis, thus causing the fluid to displace. Three-dimensional complex liquid simulations of micropump were performed. The effect of screw pitch, thread, Reynolds number and pump load on the micropump performance has been studied. The simulations of complex liquids indicate that the highest bulk velocity is achieved with high thread depth at low Reynolds number. However, effective pumping is accomplished at low Reynolds number, high pressure load and high thread depths.

Flow behaviours comparison of crude oil–polymer emulsions

ABSTRACT The flow characteristics of crude oil–polymer (COPE) emulsions were investigated in terms of viscosity and shear stress. Two commonly used polymers in the enhanced oil recovery were employed. These two different polymers are Alcoflood and Xanthan gum. Rheostress RS100 was used in this study for measuring and analysing the experimental measurements. A cone and plate sensor of RS100 rheometer was utilised for this investigation. The experimental measurements of viscosity and shear stress of different COPE were examined over the shear rate range of 0.1–1000 s−1. The polymer concentration range of 500–104 ppm was examined and two crude oil concentrations of 25% and 75% by volume were tested. A detailed investigation of the flow behaviour of COPE in the presence of two different polymers was completed. The flow behaviour of all COPE exhibit non-Newtonian shear thinning behaviour that can be presented by the power-law model for crude oil-AF1235, however the other types of COPE can be predicted by the Casson model. For a low polymer concentration of 500 ppm, this investigation showed that the flow behaviour of Xanthan emulsions is slightly higher than the Alcoflood emulsions till a shear rate of 100 s−1. For the higher polymer concentrations, both polymer emulsions exhibited more or less similar flow behaviours till the beginning of the shear thickening for the AF1285 emulsions.

Experimental investigation of the yield stress measurements for xanthan solutions and crude oil-xanthan emulsions

ABSTRACT Yield stress measurements of xanthan aqueous solutions and crude oil-xanthan emulsions were investigated experimentally. The yield stress study was carried out for wide range of crude oil (0–75% by volume) and xanthan gum (0–104 ppm) concentrations. Two types of xanthan polymers of Sigma and Kelzan were used for the current study. Aqueous solutions with higher xanthan concentration displayed higher cycles of shear rate-shear stress rheograms. Both aqueous solutions of Sigma and Kelzan showed similar behavior for concentration of ≤1000 ppm, however, Sigma solutions of higher concentrations reported slightly higher flow behavior than Kelzan. Similar rheogram behaviors are found for both Sigma and Kelzan emulsions up to concentration of 5,000 ppm. However, for 10,000 ppm, a slight higher profile for Sigma emulsions was reported.

Impact of Micro-Droplets on Superhydrophobic and Hydrophilic Surfaces

Ice accretion is a major threat to all exposed structures such as wind turbines, overhead power cables, offshore structures and aircrafts. Such deposition starts by an impact of water droplets of different sizes on the surface of the exposed structure. This work aims to shed more light on the difference in the dynamics occurring upon the impact of microdroplets on substrates with various wettabilities, hydrophilic (aluminum) and Superhydrophobic (Aluminum + WX2100) surfaces. Experiments are conducted on a wide range of diameters, between cloud sized droplets with diameters ranging down to 20μm, and 10 times larger droplets with a diameter of 250 μm. A comparison in the impact (through deformation) results is made all through the wide range and explained using the two extremes. This is done experimentally by analyzing the maximum spread diameter on the hydrophillic surface and superhydrophobic surface and maximum height as a function of time on the hydrophillic surface. Both parameters are visualized experimentally, simulated numerically for the same impact velocities and then results are compared for verification.© 2014 ASME