Droplet fall behavior

Spray Drift Aspects. The above calculations have significant implications relating to spray drift. Qualitatively, evaporative effects have been recognized for some time (4, 21). The small droplet-fall behavior... 

For the deformation of droplets of normal liquids at low impact velocities on a horizontal plane surface without phase change, Tan et al)513 developed a physical-mathematical model with a droplet falling from a certain height under the influence of gravity. They derived quantitative relations for the dimensions of the deformed droplet, including the effects of initial droplet diameter, height of fall, and thermophysical properties of liquid. In this model, the behavior of droplet deformation was assumed to be governed by... 

Deflection and disintegration of liquid droplets falling past a wire held at +6 000 V. [From D. B. Hager and N. J. Dovlchi, Behavior of Microscopic Liquid Droplets Near a Strong Electrostatic Field Droplet Electrospray"Anal. Chem. 1994,66, IS93. 

In the ink-jet method, since the material is jetted and is scattered, if a distance between a coated surface and a nozzle of a head for ink-jet is not made suitably, there can occur the problem of a so-called flying curve in which a droplet falls to a position other than intended. To overcome this undesired behavior, an improved thin film-forming apparatus has been constructed. ... 

The hydrodynamic behavior of liquid films can be characterized by the dimensionless Weber number We = (82 p g sina)/c. In Figure 4 the Weber number of a falling film (since = 1) is plotted against the activity of ethane for the system oleic acid/ethane. At low temperatures the temperature dependence of the Weber number is small. The Weber number changes little at low activities. For activities greater than 0.8 the Weber number increases sharply. The transition region from the first appearance of instability to disintegration into droplets or trickles corresponds with the sharp increase of the Weber number. 

In order to obtain a commercial loading of the near-critical extractant, the extraction is sometimes carried out at enhanced pressures in the droplet regime. In such cases the liquid phase does not flow downwards as a film adhering to the packings of a column as is usually assumed, rather it falls down as a swarm of droplets. On the basis of the separation of a mixture of partial glycerides the behavior of packed columns in the droplet regime (instable flowing films) the efficiency of different column installations are compared. A mixture of 55 wt.% propane and 45 wt.% carbon dioxide is used as an extractant. 

The only convection-free experiments are those of Kumagai and his co-workers (47,48), in which a free droplet undergoes combustion in a freely falling chamber. The observed behavior on the temporal variations of the droplet and flame sizes agreed very well with predictions from the transient analyses (36,45),... 

Three theoretical parameters were introduced by Menet et al. in order to better understand the hydro-dynamic behaviors of two-phase solvent systems [2]. We will not discuss, here, the capillary wavelength, as it only enables the description of the formation of droplets of one liquid in another liquid. The two other parameters were introduced because it appeared interesting to introduce other theoretical parameters to better describe the dynamic phenomena occurring inside a CCC column (i.e., after the formation of the droplet described by the capillary wavelength). Two of these are presented here, namely for the fall of a droplet of the heavier liquid phase (lower) in the continuous lighter one (upper) and y p for the rise of a droplet of the lighter liquid phase in the continuous heavier one, and are defined as follows ... 

In the commercial application, the drop tube method, as mentioned above, is suitable for mass production. The detailed investigations, such as temperature measurement of each small droplet and in situ observation of microstructure formation are not easy to attain because each droplet is in free fall. Here, the levitation method, where an Si droplet with a diameter of mm can be levitated by electromagnetic force using an electro-magnetic levitator (EML), as shown in Fig. 8.5, is a powerful investigation technique because the controlled droplet position enables us to measure the surface temperature of the droplet by pyrometer and to observe the crystallization behavior in situ by a high-speed video camera (HSV) [16-18]. 

The behavior of the surfactant molecules in an emulsion polymerization is complex. The adsorption of the surfactant on the rapidly and continually growing surface of the monomer-swollen latex particles reduces their concentration in the aqueous phase, and also upsets the balance in equilibrium between the dissolved surfactant and the surfactant present in the inactivated micelles (those in which polymerization is not occurring), as shown in Figure 5.11. The point is quickly reached at which the surfactant concentration in the solution falls below its critical micelle concentration, CMC. When this occurs, the inactive micelles become unstable and disintegrate to restore the balance. In time all of the micelles disappear and the monomer droplets shrink in size. After a conversion of 10-20%... 

Have you ever broken a mercury thermometer If you have, you probably noticed that the mercury forms droplets on the surface on which it falls rather than spreading out and wetting it like water. Describe the difference between liquid mercury and liquid water that explains this different behavior. (Hint Consider the attractions between particles.)... 

McNamara, J. J., "Observations on the Coalescence Behavior of Oil Droplets and Emulsion Stability in Enhanced Oil Recovery," Paper SPE 6846, presented at the SPE-AIME 52nd Annual Fall Technical Conference, Denver, Colorado, October 9-12, 1977, paper accepted for publication in Soc. Pet. Eng. J. 

In contrast, when a 2 wt.% solution of polystyrene in toluene was printed the dried droplet diameter does not show a linear downwards trend but an exponential behavior (R = 0.97). This suggests that the evaporation of toluene is halted at a certain height. The main factors that could decrease the diameter of the dried droplet on the substrate are the in-flight droplet diameter and the overall viscosity of the solution. The in-flight diameter can only be decreased by solvent evaporation, which is significant during the droplet s free fall. 

---