Droplet streams

In the second technique, two streams of microdroplets (about 100 p.m diameter, 40 kHz generation frequency, 15 ms velocity) collide to form a single droplet stream, which is observed by Raman spectroscopy. The mixing time is 200 p.s. 

Figure 5.2 shows a typical droplet stream with the last connected droplet indicated by a thin, horizontal cursor line and the stream charge collar shown as dark rectangles on each side of the droplet stream. In this view the stream flows downward and the quartz flow cell and laser optics are located out of the frame, above. 

Nonequilibrium Distillation Effects in Vaporizing Droplet Streams... 

The experimental furnace is a vertically oriented laminar flow drop tube furnace having a 30 cm long uniformly hot test section with optical access. The fuel droplet array is introduced on the logitudinal axis concurrently with the ambient gas. The droplet stream is interrupted at several points in its trajectory by a sampling probe inserted axially from the base of the furnace. The probe quenches and transports the entire flow to a sampling train which recovers the fuel droplet residue for analysis. The above process is repeated at several furnace temperatures for each fuel. A detailed description of the system is to be found in references (3) and (4). 

Experimental. To further understand the process of droplet combustion and particulate formation, a more fundamental study of the effects of droplet size, local stoichiometry and gas-droplet relative velocity has been carried out. This work made use of a controlled flow variable slip reactor in which the combustion of droplet streams can be examined under well defined conditions. 

Two extremes of droplet dispersion mode were investigated non-dispersed where the droplet stream remained tightly collimated as it traversed the reactor and dispersed, where the droplets were spread across the reactor but there was no side wall impingement. This approach allowed some control of droplet-droplet spacing and interaction from a highly collimated stream to a condition where individual droplet behavior was clearly evident. 

For all fuels tested, the overall appearance of the flame produced by the collimated droplet stream was of a narrow, luminous sheet of soot forming below the droplet stream as shown... 

In an attempt to modify the observed droplet behavior, a brief qualitative investigation was carried out with blends of SRC-II heavy distillate and pure heptane. The objective was to enhance droplet disruptive combustion as a means of reducing effective droplet size and hence soot formation. With these fuels visible droplet fragmentation was found to occur throughout the droplet stream. The fragmentation produced new droplets on different trajectories these in turn were terminated by small disruptions, as described above. Three blends were used 60/40, 80/20, and 90/10. Secondary atomization was observed for all three, although the violence of the activity was noticeably reduced as the heptane content of the blend became smaller. This secondary atomization was a completely different process than the... 

In the dispersed mode, the droplet stream was aerodynamically dispersed to permit the sooting behavior of individual droplets to be investigated. The visual appearance of the flame produced was strikingly different from the nondispersed flame. Instead of a sheet of luminous radiation down the center of the burner, the... 

Pneumatic nozzles prevail, but the spray pattern is somewhat different than found in a fluidized bed. In air suspension systems, the spray is usually a comparatively narrow, but solid cone of droplets. In a nozzle configured for perforated pan coating equipment, the initial spray pattern is also a solid cone. However, this pattern is flattened to an elliptical. shape by the u.se of. secondary atomizing air, delivered from openings adjacent to and angled slightly toward the primary atomized droplet stream (Fig. 10). In most nozzles, this secondary air is adjusted and controlled independently. The nozzle is... 

In 1879 Rayleigh (see Rayleigh 1894) was the first to demonstrate by a hydrodynamic stability analysis that a liquid jet is unstable to small perturbations and breaks up into segments that, under the action of surface tension, form into individual drops. The disturbance that gives rise to the instability may be random or forced. The current procedure of choice for the production of a uniformly sized droplet stream with uniform droplet spacing is forced longitudinal vibrations in the direction of the jet flow. 

Fig. 9. Apparatus for droplet generation and collision. The horizontal linear translator adjusts the relative phase of the droplet streams while the vertical translator is used to collide the streams. (From Simpson et...

A recent development in the production of polymer particles has created a revolutionary new technology for the production of submicron polymer particles from solution, In this experiment, generation and characterization of droplet streams with small (< 15 pm) average diameters have been used to create nano-polymer particles. This technique makes the initial volume of a dilute solution of any polymer material sufficiently small so that the solvent evaporation occurs on a very short time scale leaving behind a polymer particle. For micro and nano-scale generated polymer particles, the refractive index obtained from the data analysis is consistent with bulk (nominal) values and the level of agreement with Mie theory indicates that the particles are nearly perfect spheres. 

G. F. Christopher and S. L. Anna, Microfluidic methods for generating continuous droplet streams. Journal of Physics D Applied Physics, 40, 319-336, 2007. 

The velocity of the plasma/ droplet stream that exits the... 

A 3D liquid spraying is modeled by introducing 20 spatial droplet streams into the computational domain, as shown in Figure 10.5. In turn, each droplet stream is represented by 10 injections of different droplet diameters minimum and maximum diameters are 10.0 and 138.0 pm, whereas the intermediate droplet sizes are calculated by applying Rosin-Rammler distribution function with 70.5 pm of droplet average size as given by Equation 10.37. 

It is worth noting that the rest of the injected droplet streams demonstrate the trends similar to those given in Figure 10.21 their behavior is omitted here for space conservation. 

Loudspeakers may be employed as a source of disturbance generation in droplet on demand or continuous droplet stream generators [38]. An acoustic droplet generator is shown in Fig. 25.7 [39]. Typically, these droplet generators consist of a... 

Keywords Discrete polydisperse spray Electric droplet charging Extension nozzle Ink-jet printing Monodisperse droplet stream Monodisperse spray Multihole orifice Modulated jet excitation Nozzle hole shapes Rapid prototyping Rayleigh-type jet break-up Solder ball production... 

This section puts together the state-of-the-art of the technology for producing streams of droplets with controlled size by means of droplet stream generators. The purpose of using such devices is to produce droplets with controlled size as boundary or initial conditions for transport processes, such as in research on mechanical droplet-droplet interactions, on the impact of droplets on solid surfaces... 

Fig. 26.1 Stream of monodisperse propanol-2 droplets with highly controlled size, as produced with a droplet stream generator of the presently discussed kind. The oscillations are caused by the deformations upon pinch-off from the jet...

Droplet production by droplet stream generators takes place by pinch-off of liquid portions from jets. A trivial prerequisite for the application of this technique of drop production is, therefore, the formation of a laminar liquid jet from a round orifice or nozzle. The conditions of liquid flow through the orifice required to form a laminar jet are discussed in Sect. 26.3 below. Once the laminar jet is formed, its linear temporal instability against a disturbance with a non-dimensional wave number ka = 2nalX (with the wavelength X of the disturbance and the jet radius a) in a gaseous ambient medium under the action of surface tension, neglecting both the liquid viscosity and the dynamic interaction with the ambient gas, is described by the dispersion relation... 

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