Droplet generation

This dripping regime may continue even in the presence of low electric fields. When a high enough voltage is applied and the liquid has finite conductivity, file electric force Fe, as well as the gravitational force, will work against the capillary surface forces (i.e., Fy= Fe + Fq) and file sustainable droplet size at the capillary tip will be reduced to r (r ro). 

In laboratory electrostatic spraying or spinning, where a capillary carrying a positive voltage V is held at a distance L from a grounded metal surface. 

Fe for the system can be expressed as in equation (1.2) (Bugarski et al. 1994 DeShon and Carson 1968 Lee 2003). The expression is based on that for an electric field at the tip of a metal point and a grounded plate as proposed by Loeb et al. (1941)  

As V increases, r becomes progressively smaller until droplet instability sets in at a value of the electric field V = Vc, and electrostatic spraying occurs. 

The stability of an electrically charged droplet at the end of a capillary requires the inward surface tension forces to exceed the outward repulsion forces of like charges accumulating on file droplet surface  

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Droplet generation by air pressure differential across the film, e.g. bursting of liquid film in bubbles, froth across bottle mouths and pipette tips... 

Atmospheric-pressure chemical ionization (APCI) is another of the techniques in which the stream of liquid emerging from an HPLC column is dispersed into small droplets, in this case by the combination of heat and a nebulizing gas, as shown in Figure 4.21. As such, APCI shares many common features with ESI and thermospray which have been discussed previously. The differences between the techniques are the methods used for droplet generation and the mechanism of subsequent ion formation. These differences affect the analytical capabilities, in particular the range of polarity of analyte which may be ionized and the liquid flow rates that may be accommodated. 

Schoneeld, F., Rensink, D., Simulation of droplet generating by mixing nozzles, Chem. Eng. Technol. 26, 5 (2003). 

A complete description of droplet generator and of several atomization methods appears in a previous paper [8]. Simple air-stripping or piezoelectric drop generators were employed. The core liquid typically consisted of a polyanion solution, while the receiving bath contained a polycation(s) solution and, in many instances, a divalent cation. 

Mists Suspended liquid droplets generated by condensation from the gaseous to the liquid state or by breaking up a liquid into a dispersed state such as by splashing, foaming, or atomizing. Mist is formed when a finely divided liquid is suspended in air. 

In this chapter, various processes and techniques for droplet generation are described in detail, along with their applications and associated materials systems. 

This section describes the atomization processes and techniques for droplet generation of normal liquids. A comparison of the features of various atomization techniques is summarized in Table... 

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