Sharif Digital Repository

An experimental investigation of the flow field of pressure swirl atomizers for different pressure drops is performed. Two experimental methods are employed. For low injection pressures, a visual study is conducted while for higher pressures the velocity components and size of the droplets are measured by using Phase Doppler Anemometer. The spray formation, spray cone angle, and breakup length are visually investigated. Velocity and size of the droplets are measured on a plane of measurement along the axis of the spray so that the properties are carried out in a radial direction as a function of both pressure drop and axial distance from the nozzle. Self-similar mean axial velocity profiles... 

Radial Basis Function, a neural network based interpolation method, is used to simulate swirling spray phenomenon. From this model, the profile of mean velocity components' distribution along the main axis of the injector at various pressure drops and spray measurements' plane are obtained and analyzed. Experimental data obtained through Phase Doppler Anemometer is used to train this model. The results are compared with experimental data as well as to those obtained through General Regression Neural Network method as another neural network based interpolation method investigated previously by the authors. © 2003 by M.R. Soltani  

Multiphase flows appear in many scientific and engineering applications. On the other hand, there has been a tremendous experimental and numerical investigation trying to understand complex fluid-fluid interfaces better. However, conventional CFD have certain limitations in complicated situations. Fortunately in the past two decades, new approaches, namely SPH and LBM (sometimes called meshless methods) have been developed. Since they are mesoscopic, they have been able to perform much better than conventional CFD. Especially, LBM is becoming more and more popular and has already been divided to many branches  

Power level of a fuel cell depends on its operating condition, which is product of voltage and current-density the highest level of voltage is identified as reversible open circuit voltage (ROCV), which represents an ideal theoretical case [J. Larmin, A. Dicks, Fuel Cell System Explained, Willy, 2000 (ISBN)]. Compared to that is ideal operating voltage which is usually characterized as open circuit voltage (OCV) [J. Larmin, A. Dicks, Fuel Cell System Explained, Willy, 2000 (ISBN)]. An evaluation of deviation of operating voltage level from ideal operational case may provide information on the extent of improving efficiency and energy efficiency of a fuel cell. Therefore, quantification of... 

The mass transfer coefficients of single drops in liquid-liquid extraction systems were studied using a single drop apparatus both with and without packing. The chemical system of n-butanol-succinic acid-water and the Structured Packing (SMV.350Y) were used in the liquid-liquid extraction. Based on the experimental results obtained for both mass transfer directions, in most cases, the structured packing had considerably enhanced the mass transfer coefficient by increasing the contact area between two phases and also increasing the contact time, especially in the contaminated systems. This is an abstract of a paper presented at the 18th International Congress of Chemical and Process... 

Individual drops are suitable tools to study the liquid-fluid interfacial properties. In this work, force-displacement equation and non-linear oscillations of a pendent drop are numerically investigated. The presented novel force-displacement function allows following the dynamics of a pendent drop and realizing its elastic behavior. The growth and detachment of drop, which is pending due to gravity from a capillary tip, is considered (assuming high density and high viscosity ratios and immiscible two-phase flows). Two-dimensional multi-relaxation time lattice Boltzmann method (MRT-LBM) was used to simulate growth, detachment, and oscillations of the drop using a conservative model for... 

Drop size distribution plays a key role in the liquid extraction systems and related hydrodynamic and mass transfer parameters. In current research work, the size of drops in an extraction spray column has been measured by direct photography method, and the Sauter mean diameter has been obtained accordingly. Then, two types of models are assessed based on using dimensionless analysis and appropriate software. The interfacial tension in used chemical system is 1.8-32 dyne/cm. In first type of models, the correlation is established based on dimensionless parameters similar to approaches defined by other researchers. In second types, dimensional parameters have been used and therefore a new... 

Single drops or bubbles are frequently used for the characterization of liquid- fluid interfaces. Their advantage is the small volume and the various protocols of their formation. Thus, several important methods are based on single drops and bubbles, such as capillary pressure and profile analysis tensiometry. However, these methods are often applied under dynamic conditions, although their principles are defined under equilibrium conditions. Thus, specific attention has to be paid when these methods are used beyond certain limits. In many cases, computational fluid dynamics (CFD) simulations have allowed researchers, to extend these limits and to gain important information on the... 

In this paper, creeping motion of a viscoelastic drop falling through a Newtonian fluid is investigated experimentally and analytically. A polymeric solution of 0.08 % xanthan gum in 80:20 glycerol/water and silicon oil is implemented as the viscoelastic drop and the bulk viscous fluids, respectively. The shape and motion of falling drops are visualized using a high speed camera. The perturbation technique is employed for both interior and exterior flows, and Deborah and capillary numbers are considered as perturbation parameters up to second order. The product of Deborah and capillary numbers is also used as a perturbation parameter to apply the boundary condition on the deformation on the... 

We develop accurate analytical relations for the droplet volume ratio, droplet length during breakup process, and pressure drop of asymmetric T junctions with a valve in each of the branches for producing unequal-sized droplets. An important advantage of this system is that after manufacturing the system, the size of the generated droplets can be changed simply by adjusting the valves. The results indicate that if the valve ratio is smaller than 0.65, the system enters a nonbreakup regime. Also the pressure drop does not depend on the time and decreases by increasing the valve ratio, namely, opening the degree of valve 1 to valve 2. In addition, the results reveal that by decreasing... 

When a liquid drop impacts on a hot non-flat surface the curvature of the surface and its geometrical characteristics transmute the physical regimes and their boundary compared to a flat surface impact. The present experimental study is focused on water drop impingement on a mimetic solid semi-cylindrical convex hot surface, with a size equal to the drop. The thermal versus inertia map of generated regimes is obtained, while some well-known regimes associated with a flat surface are not observed for the present non-flat impacts. These include rebounding of the main drop and atomization which are common observed phenomena when the hot surface is flat. The maximum spreading of the droplet is... 

In this paper, an analytical solution for steady creeping motion of viscoelastic drop falling through a viscous Newtonian fluid is presented. The Oldroyd-B model is used as the constitutive equation. The analytical solutions for both interior and exterior flows are obtained using the perturbation method. Deborah number and capillary numbers are considered as the perturbation parameters. The effect of viscoelastic properties on drop shape and motion are studied in detail. The previous empirical studies indicated that unlike the Newtonian creeping drop in which the drop shape is exactly spherical, a dimpled shape appears in viscoelastic drops. It is shown that the results of the present... 

In the present study, the formation of surfactant-laden viscous drops in ambient air is experimentally investigated using a high-speed digital camera. The mixtures of 90%, 92.5%, and 95% glycerol by weight in water containing various concentrations of sodium dodecyl sulfate are chosen as the drop phase fluid. The focus of this work is to investigate the effects of concentration of surfactant dissolved in solutions with different viscosities, on physical and geometrical parameters related to drop formation process, such as the drop elongation, minimum neck thickness, formation time, and the drop volume. The formation of satellite drops and the influence of surfactant concentration on their... 

Although there is extensive experimental, theoretical and numerical research on dynamics of drop formation in liquid-liquid systems, the evaluation of mass transfer during drop formation is rather complex and there has been little research on that. The various mathematical models developed for this problem are generally based on a solution of the diffusion equation without any allowance for circulation within the drop. This is the main reason for the poor prediction of these models in many cases for which internal convection has an important effect on mass transfer rate. In this paper an attempt was made to define a parameter related to the extent of the convective mixing within the growing... 

Dynamic interfacial parameters are the key properties of interfaces in many modern technologies and can be studied in various ways. For applications like foams and emulsions, the dynamics of adsorption and the dilational and shear rheology of liquid-fluid interfaces are investigated most frequently. This work gives an insight into recently developed new experimental approaches, such as fast capillary pressure tensiometry for growing and oscillating drops. These experiments are presented in comparison to more classical techniques like drop profile tensiometry and capillary wave damping. Progress in these experiments based on generated interfacial perturbations can be expected only by a close... 

Dynamics of a drop under the influence of gravitational force was examined using lattice Boltzmann method and color-gradient model. The term associated with the buoyancy force caused by the density difference between the two phases was modified in the lattice Boltzmann equations and verified in some cases. The motion of n-butyl acetate drops in water was predicted in various deformation regimes. The modeling results were in good agreement with the experimental results, solutions obtained by common CFD methods and semi-empirical correlations. Contrary to the common multiphase models, the behavior of moving drops in oscillating regime was predicted with good accuracy using the present model.... 

Injecting low salinity brines is regarded as an enhanced oil recovery (EOR) process through IFT reduction. However, the exact mechanism behind this process is an unsettled and complex issue that has not been well understood yet, especially for heavy crude oil system. Besides, limited information is available regarding the key heavy oil/brine interfacial tension (IFT). The present study aims to investigate the sensitivity of dead heavy crude oil/brine IFT to a wide range of properties/conditions and to reveal the underlying physicochemical mechanisms involved in enhanced oil recovery and IFT reduction by low salinity water injection into heavy oil reservoir. IFT was measured as a function of... 

Injecting low salinity brines is regarded as an enhanced oil recovery (EOR) process through IFT reduction. However, the exact mechanism behind this process is an unsettled and complex issue that has not been well understood yet, especially for heavy crude oil system. Besides, limited information is available regarding the key heavy oil/brine interfacial tension (IFT). The present study aims to investigate the sensitivity of dead heavy crude oil/brine IFT to a wide range of properties/conditions and to reveal the underlying physicochemical mechanisms involved in enhanced oil recovery and IFT reduction by low salinity water injection into heavy oil reservoir. IFT was measured as a function of... 

This paper presents a new and simple algorithm for partitioning the input domain for implementation of Active Learning Method (ALM) algorithm. ALM is a pattern-based algorithm for soft computing which uses the Ink Drop Spread (IDS) algorithm as its main engine for feature extraction. In this paper a simple algorithm is introduced with a few computation cost. In order to evaluate the performance of the proposed algorithm, it is applied to two applications, system modeling and pattern recognition. Simulation results show the effectiveness of our algorithm in specifying the appropriate points for dividing the inputs domains