Papers by Keyword: Droplets

Abstract: The experiments were carried out to investigate combustion characteristics of RBL droplets (RBLD) and RBL particles (RBLP) in fluidized bed. The combustion experiments were focused on the influence of six different bed temperatures in the ranging from 530 to 780°C on gas production rates, yields of product, carbon and hydrogen conversions, releases of Na, K and Cl and emissions of NO_x and SO₂. The experiments results indicate that the combustion behaviors of RBLD and RBLP mainly depend on bed temperatures. The conversions and emissions have linear relation with bed temperature, respectively. And denitrification and desulfurization processes must be had during incinerate RBL in industry application.

Abstract: The phenomenon of laminar flow in the micro-channel is demonstrated by the software simulation. It shows different velocity produces different flow layer. Water-in-oil droplets are obtained by the experiments. These experiments take water as the dispersed phase and take the oil as the continuous phase. Analyze forming process and forming factors of the droplets and the column flow. The main factors of forming droplets are surface tension, viscosity shear force and the liquid velocity. The size of droplet is associated with the flow and channel width of two liquids. Changing the pressure of the inlet can obtain droplets in different size.

Abstract: Emulsion droplets or multi-emulsion droplet formation was important for functional materials synthesizing by microfluidic. To obtain tunable monodisperse droplets with millimeter scale, the flow regime in co-flowing channels was divided by numerical simulation. A typical co-flowing model was created using finite volume method, and the VOF (volume of fluid) muti-phase model was selected. Then, droplets were produced by changing the velocity ratio under the dripping regime. Compared to the experimental value of droplet diameter, theoretical and numerical absolute error was below 60 % and 15 %, separately. Greet agreement of diameter changing tendency was found in simulation and experiment.

Abstract: Due to its simple structure, low consumption of energy but strong driving forces, Electrowetting on Dielectric (EWOD) is used most frequently in digital microfluidics for manipulation and control of droplets. In this paper, the internal mechanism of EWOD is explained though establishing the geometric model of unipolar board structure digital microfluidic chip. The digital simulation software COMSOL Multiphysics is applied to analyze the coupling fields. The results show that external flow velocity of micro-droplet is greater than the internal velocity. Based on the theoretic analysis, surface micromachining technologies are employed to fabricate the single-plate EWOD chip. Finally, an experiment platform is set up to test this chip. Experimental results show that 2μL droplet can be driven in velocity of 10cm/s and two droplets can be merged successfully. It will possibly provide an effective solution to the manipulation of droplets.

Abstract: To study the dispersion of fuel droplets in the supersonic flow and reveal the momentum and heat exchanges between two phases, a large eddy simulation (LES) and particle Lagrangian tracking model were employed to numerically simulate two-phase mixing layer flows, using the one-way coupling method. The velocity fluctuation disturbances were added to inspire the flow instabilities. The motions of droplets in different diameters and droplets’ response to the large scale eddies were analyzed. The results indicated that droplets of 1micro diameter below are corresponded with the motions of coherent vortexes in the mixing layer. The more intense momentum and heat exchange are performed with decreasing the droplet’s diameter. The well mixing of fuel droplets in turbulence would make the combustion preparedness more sufficient. The research conclusions are of important academic value for further analyzing the two-phase dynamics in the scramjet.

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: Due to its simple structure, low consumption of energy but strong driving forces, Electrowetting on Dielectric (EWOD) is used most frequently in digital microfluidics for manipulation and control of droplets. In this paper, the internal mechanism of EWOD is explained though establishing the geometric model of the unipolar board structure digital microfluidic chip. And the boundary conditions of equations are determined. Three coupling physical fields: electric field, flow field and temperature field in the digital microfluidic chip are simulated and analyzed. With the electric field equation coupled, Navier-Stokes equations and energy equation of the temperature control, the numerical simulation of the chip is conducted. The results show that the internal flow of micro-droplets is counterclockwise and swirling flow. The external flow velocity of micro-droplet is greater than the internal velocity. In addition, micro-droplets near the electrode applied temperature are higher than the internal temperature. Surface micromachining technologies are employed to fabricate the chip. Experimental results show that the droplet can be driven in a velocity of 25cm/s. It will possibly provide an effective solution to the manipulation of droplets.

Abstract: This paper gives an historic overview and new developments of research activities in the field of the oscillatory behaviour of liquid metal in arc welding. Early work focused on the oscillation behaviour of the weld pool in Gas Tungsten Arc Welding (GTAW). Agitated weld pools exhibit specific modes of oscillation, the frequency of which can be measured from the arc voltage data and is conditioned by the geometry of the weld pool and the properties of the liquid metal. Of technological interest is the alteration of the oscillation behaviour for partially and fully penetrated situations, which can be used for penetration control during welding. A logical extension of the research activities was related to the influence of filler wire addition on the oscillation behaviour. An intermediate step towards the description of Gas Metal Arc Welding (GMAW), is the situation of GTAW with cold filler wire supply. It was found that both the liquid weld pool and the pendant liquid droplet at the tip of the filler wire experience an oscillation, which obscures the influence of the individual contributions of both liquid masses on the voltage data. It was shown that online penetration control is still possible, provided that the metal is transferred in an uninterrupted way, i.e. the filler wire flows smoothly into the weld pool. For GMAW, in which detached droplets collide with the weld pool surface, the difficulties are even more prominent. Recent work is related to this issue. Monitoring of the phenomena occurring at the weld pool and the pendant droplet become problematic by means of the voltage data. Observations by means of high-speed video imaging will be discussed. Apart from the experimental studies, efforts are undertaken in numerical simulations of the processes. A good correlation is obtained between experimental data and the results of the numerical models.

Abstract: A micropump with the function of ejecting droplet is designed and fabricated. It consists of the three components including the PZT actuator, pump body and nozzle plate. The pump body is made of the silicon while the nozzle plate is formed by nickel electroforming. The nozzle plate with single orifice is assembled to the pump body. The micropump is designed with the rectangular pressure chamber and the diffuser as the dynamic passive valve. It is driven by the PZT actuator which deflects the rectangular diaphragm through a bulge on diaphragm. The design of diaphragm with a bulge makes the assembly of the actuator easier and generates sufficient volume displacement. The volume displacement is not only predicted by ANSYS simulation but also verified by 2-dimensional laser scanning vibrometer. And, the prediction and measurement agree to some extent. The ejected droplets are observed by a visualization setup.

Abstract: Mechanisms and consequences of silicon vapor condensation during SiC epitaxial growth or implant annealing with silane overpressure were investigated. The model for the silicon liquid droplets formation in the gas phase and their deposition on the surface of the SiC substrate was developed. The droplet formation dependence on the silane flow rate, temperature profile in the reactor, and the local temperature variations introduced by the wafer carrier and SiC substrate were investigated.