Papers by Keyword: Breakup

Abstract: Pressure transducers and high-speed photography technology were applied on the experimental device which formed the axisymmetrical dissemination of glycerine. The instability development at gas/liquid interface and the primary breakup were recorded by high speed photographs. It can be concluded that the wavelength of initial disturbance waves will decrease with the incensement of shock wave intensity. At the same time, the degree of mixing of spike and airflow will also be increased. The acceleration of liquid front remains unchanged in the earlier stage and rise rapidly in the later stage.

Abstract: In this work, the shaped charge jet formation depends on different parameters which can has effect on jet behavior such as jet velocity, breakup and penetration. Jet radius or liner thickness, shell thickness, liner material density, α angle and stand-off distance are evaluated in purpose to investigate their effect on performance of shaped charge jet velocity and jet breakup phenomena, also we investigate the effect of stand-off distance on shaped charge jet penetration into steel target. We also studied the performance of some protective shields materials in order to assure more protection for vehicle structure against shaped charge jet penetration. For that, different materials were used as armors such as: kevlar epoxy, polyethylene, glass epoxy, steel-1006 and Al₂O₃ ceramic. These protective shields were evaluated in order to show their performance against shaped charge penetration into target. To do so, adopted explicit dynamic analyzing program Autodyn basing on finite element were used to simulate shaped charge jet formation and penetration. Autodyn-2D simulationshighlight the efficiency of our work comparing with the experiments done in literature and Birkhoff’s theory. In other terms, increasing in shell thickness, alpha angle and liner densityenhance jet breakup time, protective shields layered armor of steel-1006, steel 1006 with polyethylene and steel-1006 with Al₂O₃ceramic give more protection for structure against shaped charge jet penetration comparing with others armors.

Abstract: The droplet breakup is of importance in variety of spay combustion field. In order to investigate gel propellant droplet breakup in a gaseous phase, the Navier-Stokes equations in their axi-symmetric form was solved using the finite volume technique, and the Volume of Fluid method (VOF) was employed for tracking the free liquid-gas interface during process of droplet breakup. The results were compared with available published experimental data for Newtonian droplet, and validated the numerical model. The results show that increasing Weber number (We) can accelerate drop breakup; under the low shear rate, increasing K leads to droplet more resistant to breakup, drop breakup is dominated by K value; under the high shear rate, reducing n value results in stronger the shear-thinning behavior, and a decrease in resistant to breakup, n value governs the droplet breakup.

Abstract: A Volume of Fluid (VOF) method is used to study the breakup of droplets in T-junction geometries. Symmetric T-junctions, which are used to produce equal size droplets and have many applications in pharmacy and chemical industries, are considered. Two important factors namely "breakup time" and "breakup length" that can improve the performance of these systems have been introduced. In addition a novel system which consists of an asymmetric T-junction is proposed to produce unequal size droplets. The effects of the channel width ratio and the capillary number on the size and length of the generated droplets and also the time of the generation have been studied and discussed. For simulation the problem, a VOF method used and for verifying the accuracy of the simulation the results compared with two analytical researches and a good agreement was found. The results indicate for the systems that generate equal size droplets, in a specific Capillary number (in our case 0.02) the performance of the system is in its optimum condition. Also for the systems that generate unequal size droplets, in large capillary numbers a wider range of droplets with different sizes can be produced.

Abstract: Modern solid-propellant rocket motors (SRM) are laden with aluminum powder to increase the specific impulse. In SRM chamber, on the one hand, aluminum droplets evaporate and burn to form alumina smoke, on the other hand, the alumina smoke agglomerates to droplets as droplets collide with each other. The agglomeration model is employed to simulate the burning droplets. And breakup model also used. To avoid complex reaction theory, the article solves the mass, momentum and heat equations of disperse and continuity phases to simulate the chemic reaction. Results showed that burning efficiency and agglomeration of droplet varied by different initial diameters, and the temperature as well as smoke concentration also changed, especially in nozzle inlet.

Abstract: Oil droplets can break up during flight and form many secondary droplets in an aero-engine bearing chamber due to aerodynamic drag forces. The motion properties of secondary droplets have significant influence on the two-phase oil/air flow phenomena in bearing chambers. In this work, oil droplet trajectories and velocities are developed by accounting for in-flight breakup. The droplet motion is modelled using a Lagrangian tracking method, and the trajectories and velocities are calculated by numerical integration of the oil particle momentum equation with forth-order Runge-Kutta scheme. The trajectories and velocities change abruptly at the breakup location, compared with unconsidering breakup. Subsequently, the effects of operating conditions on oil droplet motions are discussed. The numerical results show that the influence of breakup on oil droplet trajectory and velocity are considered necessarily when simulating two-phase oil/air flows in bearing chambers.

Abstract: Droplets transport in homogeneous porous media has been found to be an attractive problem applicable in a lot of industrial and scientific sectors such as enhanced oil recovery, food production, plastics etc. As applications become wider, a predictive method for the process is warranted. To this end, it has been widely accepted that the collection of γ-order moments, Sγ, can describe the time evolution of any spatially averaged quantity like the mean diameter of spherical droplets, while it has been also found that Sγ satisfies the transport equations [1]. Here, the so-called “Sγ concept” is applied in a CFD module for the modeling of the transport processes occurring in a mixture of a continuous aqueous phase which includes a discontinuous one in the form of droplets. This mixture flows within a homogeneous porous medium under creeping or laminar flow conditions. The momentums of the particle size distribution are evaluated using the local flow conditions as obtained from CFD simulations for the processes considered. To solve the transport equations, the microstructure droplets formation/destruction has been also taken into account by using already known analytical expressions for the source terms representing the break up and coalescence of the droplets [2-4]. The proposed constitutive model adequately simulates the effect of porous geometry on the droplets size distribution and could be helpful in understanding the phenomena that take place in microscopic scale.