Sharif Digital Repository

Drop penetration into the capillary tube, as a classical problem, has been studied over 100 years. But there are a few studies that investigate forced impregnation of capillary tubes, which has major application in coating, inkjet printing and rain drop penetration into the soil, have been made. A comprehensive numerical investigation on millimeter droplet impact dynamics on a thick capillary tube with micrometer sized pore is conducted and validated against experimental data. This work is extended to oblique impact of drops into pores and normal impact on nanoscaled pores. We apply the finite volume numerical method to solve the time-dependent governing equations of continuity, momentum in... 

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 the mimetic solid semi-cylindrical convex and concave hot surfaces. 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. The maximum spreading of the droplet is measured at different surface temperatures and impact Weber numbers for the case of droplet impingement on the convex surface. In directrix... 

Drop formation from the tip of a nozzle and its motion in bulk fluid is an interesting and practical process which has widely turned researchers’ attention. Investigation into the governing physics and effective parameters on formation, deformation and motion of a drop increases the efficiency of the related industrial processes. Thus in the present study, in order to simulate this process, full Navier-Stokes equations solved by the Volume of Fluid (VOF) method in an axisymmetric domain using Fluent software as the solver. In this research, the effects of Weber number (the proportion of inertial force to surface tension force) and Ohnesorge number (which refers to the proportion of viscous... 

In this paper, we introduced two methods for producing unequal sized droplet from an initial one that don’t have the disadvantages of the available methods. We developed a comprehensive analytical theory for the T-junction with valve method. Also the geometry was simulated using a VOF algorithm and a comparison was performed between numerical and analytical results and very good agreement was observed. The accuracy of numerical results was confirmed by doing the grid independency and time step independency and comparing the results with two analytical benchmarks. We derived accurate analytical relations for calculating the droplet volume ratio, droplet length (L1, L2 and Lwhole) and pressure... 

Injection of liquid fuel in the cross-flowing air provides a means of higher penetration, rapid mixing of liquid fuel and air, and is encountered in many engineering applications. Air-breathing propulsion systems (e.g. gas turbine combustors, ramjets, and scramjets), liquid rocket engines,cooling sprays for turbine blades, and injection of fuel in the afterburners are examples of such applications. The identification of microscopic characteristics is one of the basic methods of atomizer examination, which has not been taken into account due to inadequate experimental equipment. In the present study, droplet mono-frame velocimetry and size distribution of secondary atomization in a pressure... 

In this research, the characteristics of non-Newtonian, shear-thinning drop formation containing surfactant from a needle are investigated experimentally. The ambient fluid is air and all experiments have been conducted in a constant flow rate of drop phase fluid. Images of forming drop are taken using a high-speed camera and by processing them, important parameters in drop formation such as length of drop, minimum neck thickness, formation time and the size of satellite drops have been studied. Three non-Newtonian and three Newtonian fluids are considered in a way that the initial viscosity of non-Newtonian fluids would be equal to the viscosity of their corresponding Newtonian fluids.... 

Spray-wall impingement is one of the phenomenon that associated in different subject such as spray cooling, combustion chamber and gas turbine. With the impingement of spray to the wall, liquid film begins to form. Wall film characteristics is still an important subject to study. Due to the various stages of liquid film formation from injection of spray till spray-wall impingement, the investigation of this phenomenon is far more complicated. This paper is meant to provide detailed data on spray-wall impingement and wall film formation physics with the help of computational analysis of OpenFOAM . A Lagrangian-Eulerian method based on discrete phase model (DPM) was employed to model... 

The purpose of this research is the synthesis of nanoparticles using micro fluid glass.The microfluidic glassy building is studied. Glass microfluidic microchannels making hydrophobic the continuing experiments carried out so that the water droplets in the organic phase and at the end of nanoparticles should be synthesized. Tests hydrophobic microchannels and water droplets in the organic phase was formed. In order to ensure an escape water contact angle and FTIR micro-channel test is taken and to avoid the droplets merged with each of surfactant SDS was used. In the end, DLS and FESEM nanoparticles synthesized using the tests have been evaluated and the concentrations of reactants and flow... 

Formation and detachment of drops are of fundamental importance in studying two-phase flows, such as ink jet printing, emulsion, and spray. Drops are formed under the effects of surface tension forces. After formation, forces like gravity detach the drop from the rest of the fluid. The flow rate is varied from dripping to jetting regime. In this project, formation and detachment of drops were simulated, using LBM with phase field model, which can simulate flows with high-density ratios and is a robust method for applying wetting condition on the walls. Results were validated using single-phase and two-phase flows. After code validation, the oscillations caused by formation and detachment of... 

Polymeric microspheres which can load biomolecules, proteins and growth factors play an important role in tissue engineering and drug delivery systems. The size of the microspheres and encapsulation efficiency exert a considerable impact on the usability of them. In this study double emulsion method is used for fabrication of microspheres. Effect of different parameters namely the speed of homogenization, time of homogenization, the amount of polymer in oil phase, the surfactant concentration in different phases on the size and surface morphology of the microspheres are investigated. Moreover, a release test for BSA loaded microspheres is conducted. Results indicate that by increasing the... 

A new microfluidic device is introduced for sorting the particles based on the hydrodynamic resistance induced in a microchannel which is not needed for additional detection or sorting modules. Hydrodynamic resistance affects physical properties, such as size and deformability of the particle. This device could apply application in cell sorting for remedies, diagnostics, and industrial applications. The device design is performed using an equivalent resistance model, and also numerical simulations are performed. For validation of the results, they are compared with experimental results. Moreover, we will discuss threshold particle size and will introduce a way to approximate it to ... 

One of the key features of multiphase flow applications is the creation of as little liquid droplets as possible. For example, it is important to use combustion to burn liquid fuels in combustion chambers, fuel-air mixing and complete evaporation of fuel. Liquid fuel should be converted into small droplets and then mixed with air quickly and evaporated. This challenge has been investigated using injectors of various designs and is still being investigated. One of the injectors used is injectors where both gas and liquid are injected into the injector and supplemented with each other. These injectors are referred to as focal injectors, in which gas flows through a typical orifice to... 

In the present work we first introduced ILIDS and review the theory of interferometry and light scattering from droplets. Bases on ILIDS method, droplets are irradiated by monochrome sheet laser, where the superposition of reflected and first-order refracted beams form a parallel fringe pattern at out of focus plane on the imaging sensor in the forward-scatter region. This pattern can be related to the droplet size by using simple geometrical optics. For the present work, an image processing algorithm is utilized to capture weak and noisy images of droplets to reduce the lost data in the sizing procedure. Since ILIDS method is applied for small and dilute spray, it is suitable for... 

Symmetric T junctions have been used widely in microfluidics to generate equal-sized microdroplets, which are applicable in drug delivery systems. A newly proposed method for generating unequal-size microdroplets at a T junction is investigated theoretically and experimentally. Asymmetric T junctions with branches of identical lengths and different cross-sections are utilized for this aim. A novel equation for the critical breakup of droplets at asymmetric T junctions and one for determining the breakup point of droplets are developed. A good agreement was observed between the theories (novel and previous) and the experiments