Number Of Satellite Droplets Research Articles

Effect of drainage device on the transition of dripping and jetting modes

The formation of droplets is a part of many practical engineering problems. Satellite droplets are harmful in the production of traditional Chinese medicines, ink-jet printing, and electronic packaging. It is necessary to investigate the methods to eliminate the satellite droplets. A drainage device was added to the dropper to suppress the formation of satellite droplets. This paper investigated the effects of liquid physical parameters and drainage devices on the fracture length of the neckline and the main-droplet diameter. The effect of the diversion device on the ligament was analyzed using the scaling theories of the Pinch-Off. The effect of the drainage device on the transition of the fluid from the dripping mode to the jetting mode was also investigated. After adding the drainage device, the fracture length of the neckline, the main-droplet diameter, and the number of satellite droplets are significantly reduced. The fracture length of the neckline and the main-droplet diameter decreased with the increase in the length and diameter of the drainage, but the fracture length increased with the increase in liquid depth. With the rise of glycerin mass fraction, the fracture length of the neckline increases, whereas the main-droplet diameter decreases.

A Conservative Level Set Approach to Non-Spherical Drop Impact in Three Dimensions.

A recently developed conservative level set model, coupled with the Navier-Stokes equations, was invoked to simulate non-spherical droplet impact in three dimensions. The advection term in the conservative level set model was tackled using the traditional central difference scheme on a half-staggered grid. The pressure velocity coupling was decoupled using the projection method. The inhouse code was written in Fortran and was run with the aid of the shared memory parallelism, OpenMP. Before conducting extensive simulations, the model was tested on meshes of varied resolutions and validated against experimental works, with satisfyingly qualitative and quantitative agreement obtained. The model was then employed to predict the impact and splashing dynamics of non-spherical droplets, with the focus on the effect of the aspect ratio. An empirical correlation of the maximum spread factor was proposed. Besides, the number of satellite droplets when splashing occurs was in reasonable agreement with a theoretical model.

Experimental Study of the Solder Paste Jet Printing Process Using High Speed Photography and Rheological Methods

The jet printing process of Sn-58Bi lead-free solder paste involving expansion, necking, pinch-off and satellite droplet formation was observed and analyzed with the aid of high-speed photography. The viscosity and phase angle of the solder paste at three temperatures were measured using a rheometer. Spattering behavior of the solder paste was observed at 55°C. The spatter on the substrate came from a second satellite droplet which was produced in the second pinch-off of the solder paste and collided with the nozzle. Satellite droplets were produced at three temperatures when droplets break off, and the number of satellite droplets was determined at each temperature. The appropriate temperature could reduce the viscosity of the solder paste and improve the liquid-like behavior, which is conducive to realizing the jet printing process with an ideal ratio of height to diameter of the solder joints. According to the demand for jet solder paste, high-speed photography and rheological methods can help establish the relationship between jet printing performance and materials design.

Dynamic nozzles for drop generators.

In this paper, a novel mechanism allowing greater control over the formation of droplets is presented. This is achieved via the use of a dynamic nozzle of adjustable diameter. It is demonstrated that, by using such a nozzle, it is possible to greatly modify the formation and breakup of the ligament behind the main drop, leading to an overall reduction in the number of satellite droplets. Furthermore, by adjusting the delay between the beginning of the forming of the drop and the start of the nozzle constriction, a greater control over both the number of satellites and the size of the main drop can be achieved. It is also shown that only a minimal reduction of the nozzle's effective diameter is required in order to exploit the positive effects of the technique presented here. This opens the possibility of incorporating the technique into current droplet generator systems, e.g., via the use of piezoelectric driven nozzles or other micro-mechanical actuation technology.

A PARAMETRIC NUMERICAL STUDYOFTHE HEAD-ON COLLISION BEHAVIOR OF DROPLETS

Head-on collision of droplets consisting of different liquids for a wide range of Weber numbers between 25 and 430 is studied numerically using the volume of fluid (VOF) methodology and by adopting an axisymmetric approximation. An adaptive local grid refinement technique is used to capture with precision the liquid–air interface at significantly reduced computational cost relative to a uniformly dense grid. The conditions setting the boundary between permanent coalescence and reflexive separation are defined; in addition, useful relationships determining the ligament’s elongation, the corresponding time of its breakup, the number of satellite droplets formed, the maximum droplet deformation, and the viscous dissipation coefficient are presented. Furthermore, the present study reveals the dependence of collision characteristics not only on Weber number, but also either on Reynolds, capillary, or Ohnesorge numbers.