Droplet transport

The complete LDA system includes the appropriate transmission and detection optoelectronics, traverse mechanisms, computer-controlled signal processing, and a data acquisition and evaluation system. The LDA equipment is a powerful tool for the measurement of flow velocity and velocity fluctuation, as well as the local concentration of particles or droplets transported in the airflow. 

It is known that, in a water phase, immiscible liquids such as gasoline or other petroleum products may form multicomponent droplets of various forms and sizes, under dispersive conditions. These droplets are transported by convection and diffusion, which contributes to the contamination of fresh water systems. However, during droplet transport, more volatile substances partition to the gas phase at the droplet surface, leaving less volatile material that volatilizes more slowly. More volatile material still exists in the droplet interiors, and it tends to diffuse toward the surface because of concentration gradients created by prior volatilization. Different components in a droplet have different volatilization rates, which may vary significantly during droplet transport, and as a result, the contamination of fresh water is affected accordingly. 

Gupta, A. K., C. Presser, J. T. Hodges, and C. T. Avedisian. 1996. Role of combustion on droplet transport in pressure-atomized spray flames. J. Propulsion Power 12(3) 543-53. 

A widely held doctrine has been that both wind and small droplets are an anathema to aerial spraying in that both significantly enhance drift. While "common sense" appears to support these convictions, analysis of the mechanisms of droplet transport and impaction reveals that, under most circumstances, quite the opposite is true. 

M 14] ]P 14] For electrode arrays of different pitches with fixed geometric ratios the threshold voltage and the droplet transport, i.e. the velocity-voltage function, did not change [98]. 

Figure 1.38 Effect of the medium on droplet transport. The threshold value for droplet movement (900 nl 0.1 M aq. KCI) is given by the x-axis intercept. [97] (by courtesy of RSC).

P 16] Sequential voltages with six-phase rectangular profiles were applied [100, 101]. Following some first evaluations, it turned out that the sequence [+++ -] was the most efficient means for droplet transport. Most smooth droplet transports were found for voltages > 350 V. The upper limit was, however, fixed at 400 V, since otherwise cross-electrode discharge may lead to damage. 

M 16] [P 16] Droplet transport could be achieved for frequencies of the sequential voltages in the range 0.5-3.0 Hz [100, 101]. An increase in the ratio of electrode width to pitch facilitated the droplet transport. Since only perpendicular transport can also be achieved, fluid guiding is necessary. This can be accomplished, e.g., by use of thin polymer films. 

Reverse flow measurements in the wake of a stabilizer disk show increases in size and magnitude of the maximum reverse flow velocities within the recirculation zone as a result of combustion. Evidence was found of initial pilot burning in the recirculation zone from combustion of flne droplets transported by the reverse flow. 

Release from vesicle Release from water droplet Transport across oil phase... 

H. Ren, Electrowetting-based sample preparation an iiutial study for droplet transportation, creation and on-chip digital dilution. Ph.D. Thesis Duke Uiuversity (2004). 

Applications based on EWOD are in the development phase and quite close to market produets. For example, an enz5miatic colorimetrie assay for (point-of-care) diagnostie applieations has been successfully implemented, and glucose concentration in several biologieal liquids (serum, plasma, urine, and saliva) was determined with eomparable results to standard methods [265]. The mierofluidie ehip layout for the eolorimetrie glueose assay is depicted in Fig. 16. It features reservoirs, injeetion stmetures (metering) and a network of eleetrodes for droplet transport, splitting and deteetion. 

These electrowetting chips are used to dispense the sample and the reagent droplets, transport and mixed them for chemical reactions to occur. 

The one-dimensional droplet transport model, presented as above, is somewhat generic in nature and can take special forms depending on the specific modes of droplet motion actuation. For example, one may consider the thermocapillary-driven droplet motion in a cylindrical capillary, in which the surface tension varies as a function of the local temperature. For small temperature variations, this dependence is approximately linear and can be described as... 

Description The special hydrod3mamics of droplet transport cause a pairwise alignment of the droplets. For this particular configuration, the smaller droplet is automatically placed in proximity to the larger droplet and is kept at this position by the wall friction-driven recirculating flow of the continuous phase. Hence, droplets are transported as droplet pairs and can be directly merged at a target position by electrical field actuation. 

Limitations Volumetric precision of the described dosing process strongly depends on the uniformity of the droplet distance and transport velocity of the target droplet sequence. Therefore, this approach can be employed for assays, which are performed in continuous flow mode and strictly serial droplet transport regime. 

Both platforms for droplet microreactors require the following key functimis for manipulating droplets droplet formation, droplet transport, mixing inside droplets, droplet merging, and droplet splitting. In the following, the basic methods for obtaming these functions are discussed. 

Ren H, Fair RB, Pollack MG, Shaughnessy EJ (2002) Dynamics of electro-wetting droplet transport. Sens Actuators B 87 201-206... 

Lee CP, Chang HC, Wei ZH (2012) Charged droplet transportation under direct current electric fields as a cell carrier. Appl Phys Lett 101 014103... 

Droplet Traffic in Microfluidic Networks Traffic of droplets (without splitting and merging) in a dual network can also be simulated in a similar method, which contains transport channels for droplet transport and bypass channels that cannot be accessed by droplets. Figure 1 shows three recently proposed devices for droplet traffic analysis a reversible encoding loop (Fig. la), a bypassed Y-junction for symmetric... 

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