Papers by Keyword: Droplet

Abstract: A method is described to determine geometrical dimensions of electrode metal droplets depending on short circuit duration. It provides a quantitative evaluation of the electrode metal transfer and the energy impact on metal parts being welded. It is proved that using inverter power source decreases the size of droplets transferred to the welding pool by 24% in average if compared with a diode power source. It also reduces overheating of the droplets which improves efficiency of transferring chemical elements from the electrode to the weld metal.

Abstract: The general method to remove contaminated particles in the non-pattern cleaning such as pre-photo cleaning, post-deposition cleaning, and post-CMP cleaning is to physically remove particles using spray nozzle. However, high-speed fluids for increasing particle removal efficiency cause static electricity due to friction between liquid and nozzle surfaces, resulting in unexpected charge defects. In this study, we propose a method to reduce static electricity by changing the material of nozzle and grounding by visualizing static electricity according to electric voltage.

Abstract: This work is devoted to investigation of the way light transmittance of drying drop of Fe₂O₃ nanocolloid deposited on flat surface changes as liquid evaporates. According to results of transmitted light intensity measuring it is assumed that drying process can be divided into separate stages each being characterized by particular quality level of ability to transmit light because of different behavior and, thus, density of suspended nanoparticles inside the droplet. The last stage ends by forming of a ring-shaped pattern (known as “coffee ring”). Temperature of the surface was being changed by applying a varying potential difference to lower layer of transparent substrate made of ITO. Time dependences of integral transmitted light intensity for every single temperature are represented in graphs. They are compared with dependences for water drops of the same volume.

Abstract: Under excitation of high-voltage pulse electric field, the deformation vibration of droplet in oil was very important to electro-dehydration of emulsified oil. So far, the theoretical calculation on vibration of droplet was scarcely studied. In order to calculate the vibration of droplet, the forces acted on a single droplet needed to be analyzed, and the vibration kinetic model of droplet needed to be established. The model was resolved by method of harmonious wave balance. It was found by analysis that the resonance of droplet might occur. In the experiment, the results approximated to that of model calculation. So it was verified that the model could efficiently calculate the vibration amplitude of droplet.

Abstract: Three typical solution schemes of adjoint problems of heat transfer, phase transformations and chemical reaction at the forest fuel material surface were analyzed in this work. Characteristic times of thermal decomposition reaction suppression of forest fuel materials (needles of pine and fir-tree, leaves of birch) were presented for concerned heat transfer models. Effective heat exchange conditions which are characterized by minimal times of chemical reaction suppression in forest fuel materials and minimal extinguishing agent's expenditure were established.

Abstract: Modern internal combustion (IC) engines employ a variety of injection techniques for preparing a combustible mixture of fuel and air. In a fuel injection-based system, the vaporization of the atomized hydrocarbon fuel droplets has significant influence on engine performance and emissions. The entropy generation associated with droplet vaporization is particularly important as it is directly related to the destruction of exergy i.e. the potential to produce useful work. Since a fuel spray could involve millions of droplets, solving the entire set of governing equations for individual droplets in a spatiotemporally discretized domain is impractical. The present work explores the utility of a simple phenomenological model in predicting the entropy generation history. The results indicate that this model ensures computational efficiency without much sacrifice in accuracy.

Abstract: A low dimensional precision is one of drawback for the GMAW-based rapid forming technique, which is related to pressure and heat flux on molten pool. To study pressure and heat flux on molten pool, the effect of droplet impinging process must been considered. A three-dimensional numerical model was built to analysis pressure and heat flux distribution on molten pool. Solving the model, it was found that pressure on the cathode by the arc decreases dramatically when the droplet is coming. As to heat flux, the appearance of droplet cuts down it within about 1.5 mm away from arc axial. Out of 1.5 mm away from arc axial, droplets effect on heat flux is not obvious.

Abstract: In order to achieve high efficiency of new fuel engine, a mathematical model based on mass, momentum and energy equations was developed to describe the motion and evaporation characteristics of a single ethanol droplet in high temperature nitrogen environment. By comparing the numerical results with experimental data, the validity of model was confirmed. The relationships of droplet temperature, velocity, size with time and movement distance under different ambient pressures were analyzed. The calculated results indicate that with a higher ambient pressure, the droplet temperature is higher, the droplet velocity declines faster, the movement distance is shorter; the evaporation rate is slower, and the droplet life is longer. Within the distance where the droplet velocity continuous variation, the droplet temperature rises gradually, the droplet size expands slightly, and with the increase of ambient pressure, the droplet expansion is more significant.

Abstract: Experimental investigations of combustion of droplet and vapour mixtures under quiescent condition have been conducted in a closed combustion vessel. Droplet and vapour mixtures or aerosol mixtures were generated by expansion of iso-octane gaseous pre-mixture to produce a homogeneously distributed suspension of fuel droplets. The aerosol mixtures were ignited centrally in the combustion vessel and the flame development was recorded by schlieren photography. The effect of fuel droplets in the early stage of flame propagation was investigated by comparing the flame structure and flame speed of gaseous mixtures at identical conditions. Comparison between gaseous and aerosol flame have shown quantitatively that the presence of fuel droplets causes earlier onset of instabilities and cellularity than for gaseous flames, particularly at rich conditions. This difference was shown to be a function of droplet size and overall equivalence ratio. It is suggested that these factors lead to vary the local equivalence ratio which increases the initial burning rate of lean aerosols, but decreases that of rich ones.

Abstract: A method for a droplet transportation by jumping a obstacle on piezoelectric substrate is presented, and a device for the droplet transportation is implemented on a 128° yx-LiNbO₃ piezoelectric substrate. An interdigital transducer and a reflector are fabricated on the piezoelectric substrate using microelectric technology. Hydrophobic film is coated on the area free of electrodes and a polydimethylsilicone obstacle is mounted on it. A radio frequency signal amplified by a power amplifier is applied to the interdigital transducer to generate surface acoustic wave. When the surface acoustic wave meets with the droplet on the piezoelectric substrate during transportation, part of acoustic wave enegy is radiated into the droplet, leading to internal acoustic streaming. Once the radio frequency signal with appropriate amplitude is suddenly decreased, part of the droplet will jump the obstacle due to interial force. Red dye solution drops are demonstrated for transportation experiments. Results show that a droplet can be transported from one side to another of the obstacle on piezoelectric substrate by help of surface acoustic wave. The presented method is helpful for microfluidic system on a piezoelectric substrate.