Sharif Digital Repository

In this thesis the instability regimes of the liquid sheet resulted from interactions of three converging jets is investigated. To this end, the shadowgraphy method is used. All the experiments have been done under the atmospheric pressure by using water as the jet fluid. The injectors are orifice ones.In our study, the effects of changing the jet velocities and changing the three jets’ structure (planar and non-planar) in having different liquid sheet shapes are investigated.Although so many researches have been done on interactions of two converging jets until now, there is almost not any researches about interactions of three converging jets. Considering this, this thesis topic is novel,... 

Liquid atomization have broad range of usage in different industries. Colliding two jets is one method for atomization of different kind of fluids especially high viscose and viscoelastic fluids. Here, we experimentally investigated the effect of skewness and velocity differential of two Newtonian viscose colliding jets on formation of a special oscillating liquid sheet pattern with periodic fragmentation called “fishbone”. For this work, four liquid sheet regimes; triple chain, double chain, close rim, and open rim which fishbone pattern could be observed were produced and Skewness and jets velocity differential were applied to them. A synced CCD camera and stroboscope illumination source... 

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... 

The velocity of the hot outflow gas in laminar premixed flame is one of the important properties of combustion, along with other properties such as temperature and flame components. In fact, laminar flame velocity has been employed in a multitude number of concepts ranging from engine design to achieving flame properties under turbulent conditions. In this research, a cylindrical Bunsen burner and appropriate TIO2 particles were used. Particles with diameters between 10-23 microns were used and the exit diameter of burner considered 14 mm. In this study, the equivalence ratio with a value between 0.9-1.2 are fed with LPG fuel to create a laminar premixed flame. As a result of the present... 

In most of the studies conducted on the physics of the outflow from impinging jet injectors, Newtonian fluids have been used for their research and experiments. These studies have investigated the effect of factors such as geometrical parameters of the injector and physical properties of the fluid on different regimes resulting from the impact of the jet stream; Unfortunately, very few studies have been conducted on how to form spray and atomization in gel non-Newtonian fluids containing nanoparticles to investigate the above factors when using impinging jet injectors. Furthermore, although the addition of nanoparticles has advantages for better combustion, there are still problems in... 

Injecting liquid fuel into the cross flow of air provides high penetration of the liquid, rapid mixing with air, and increased efficiency. This method has widespread applications in the propulsion systems of gas turbines, scramjets, turbine blade cooling, and fuel injection for engine afterburners. One of the design strategies for future aircraft engines is to reduce pollutants using fuel spray into the cross flow instead of direct jet fuel injection and using renewable energy sources. The applications of cross flows include injecting fluid through rotating pressure injectors in exhaust flows, injecting fluid through pressure-rotating injectors in radial injectors, and using slinger... 

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... 

The Chemiluminescence method is considered as one of the most widely optical methods that used for identifying combustion systems. In this study, the OH^* and CH^* Chemiluminescence signals were measured with the use of PMT detector and other optical equipments for a bunsen burner. Also the effect of equivalence ratio and flow rate on these signals have been investigated. The results show that with increasing flow rate, OH^* and CH^* signals increase linearly. By changing the equivalence ratio, both signals were maximized near stoichiometric condition (OH^* in lean side and CH^* in the rich side). Therefore, both OH^* and CH^* are considered as indicators of released heat rate. It was also... 

The use of liquid metal droplets due to their high electrical and thermal conductivity are used in various industries today. One of the methods of producing these micro-droplets is the flow focusing method, which is widely used to produce integrated and monodispersed droplets. Liquid metals have high surface tension and these micro-droplets are formed only if there is sufficient shear force between the liquid metal and a continuous fluid phase. In the past, they used several different methods such as pressure fluctuations and changes in continuous phase flow rate to control the shear force and produced polymer, gas, etc. micro-droplets.In this research, use the electric potential to control... 

Due to the large application of electro-sprays in various industries, the study of the stability of electro-hydrodynamic flows is important. This thesis examines the stability of cylindrical liquid jets in the presence of an axial electric field. The definition of this jet is a simplified model of electrospray, electrospinning. In this model, the stability of a free incompressible cylindrical flow with surface tensile strength, conductivity, polarization, viscosity, and dielectric constant is determined, irrespective of the solubility of the jet and the surrounding fluid (air), in the presence of uniform axial electric field has taken. This will be done by adding the forces generated by the... 

In This thesis, the behavior of flow inside the pressure-swirl atomizers is studied. The pressure-swirl atomizers are widely used in many industrial applications such as fuel injection in gas turbine, internal combustion engine and liquid-fuel rocket, spray drying, spray in firing and agricultural nozzles.The flow simulation inside the pressure-swirl injector deals with many complicated considerations due to air core formation in the axial zone of the injector as well as high tangential and axial velocities in the swirl camber. The ANSYS Fluent commercial program is used for simulations. The two phase flow inside the injector is modeled by volume of fluid method (VOF) using large eddy... 

In this thesis, the physics related to liquid jet injection from injectors with three different crescent-shaped cross-sectional levels into steady and transverse flow were studied. The imaging method in this research was based on shadowgraph, which enables high-speed imaging. With the help of the obtained images, the breakup regimes, including Rayleigh, first and second wind-induced instabilities, were observed for injection into the steady flow. Furthermore, breakup regimes for jet injection into transverse flow, including columnar, columnar-bag, and bag, were also observed. The characteristics of the breakup height in steady flow and the length and height of the breakup along with the jet... 

Based on the history of computational fluid dynamics, choosing a proper method for three-dimensional investigation of two-phase flows is always challenging. In this research, the flow of atomization of a liquid jet was investigated. Also, Using GPU technique made our computations about 40 times faster. The numerical results are in good agreement with available numerical and experimental data. Based on our results, jet flow can achieve different regimes at different Weber and Reynold. Jet flow was found in dripping and Rayleigh instability regimes when Weber number was set to 1.79 and 3.10, respectively. Also, the transition between dripping and jetting was estimated at We between 2 to 3. In... 

An injector is one of the most important components of the two components chemical propulsion system used in satellite control. The design of an injector is a complicated and time-consuming process and is largely dependent on laboratory data. In this study, the spray characteristics obtained from a small scale swirl injector under different operating conditions have been experimentally measured in a laboratory environment, such as the injector discharge coefficient, spray cone angle, and the distribution of droplets in the field. To calculate the discharge coefficient, the flow rate of the injector has been measured for different operating pressures. The shooting method and image processing... 

Iin this thesis, evaporation of droplets of a spray from a pressure-swirl injector in a sub-atmospheric combustion chamber is studied. The liquid used in this sudy is a hypergolic oxidizer, Dinitrogen Tetroxide, also known as NTO. The significance of this thesis is its application during the cold startup of a satellite thruster when only oxidizer is injected into the combustion chamber. The most important phenomemon in this stage which is also the focal point for this study, is the ‘Flashing’. In this phenomenon a liquid having a temperature above the boiling point of its own species (for the surrounding gas pressure) is present in the solution field. This state is a non-equilibrium state.... 

In this thesis to simulate the behavior of liquid engine Thrust chamber of hot gas from a quasi one dimensional code used when the effects of the heat transfer and friction in those terma. As well as during the regenerative channel is simulated by considering the equation’s of continuity, momentum and energy for one dimensional, effects of increase temperature, pressure drop, change the density of coolant flow resulting from the warming which is visible along the way to increase the accuracy of calculation of the thermal flux output of the engine, use a suitable model for unclear boiling in consideration of heat transfer coefficient used coolant flow it has been. As well as coupling of heat... 

With the increase in the average age of the world's population, osteoporosis is a worldwide incidence. This disease, along with natural disasters, are important factors in the occurrence of fractures in various bones of the body. One of the methods for solving this problem and replacing with broken body bones is the use of metal implants with hydroxyapatite-based coatings. One of the common problems with using implants in the body is the infection in the adjacent parts of the implant. To overcome this problem, several studies have been carried out on the use of hydroxyapatite coatings with metal ions or antibacterial oxide compounds. In the present study, the influence of factors such as the... 

Quantitative measurement of pressure on surfaces in wind tunnels and flight tests is essential to understand the aerodynamic performance of flying vehicles. Pressure data are also essential for validation and verification of computational fluid dynamics codes. One of the relatively new methods of measuring pressure distribution on aerodynamic surfaces is the method of pressure sensitive paint (PSP). The PSP method is an optical technique that can measure the pressure distribution on the surface without using common pressure sensors or transducers, with greater spatial resolution and lower cost. This method has a unique ability for non-contact (non-interfering) measurements. In this method,...