Extraction drop diameter

Drop Diameter. In extraction equipment, drops are initially formed at distributor no22les in some types of plate column the drops are repeatedly formed at the perforations on each plate. Under such conditions, the diameter is determined primarily by the balance between interfacial forces and buoyancy forces at the orifice or perforation. For an ideal drop detaching as a hemisphere from a circular orifice of diameter and then becoming spherical ... 

The two graphs for each medium represent the bounds of drop sizes in the range of applied extraction conditions. A maximum drop diameter in the distribution is considered (equation 5). 

Industrial liquid-liquid extraction most often involves processing two immiscible or partially miscible liquids in the form of a dispersion of droplets of one liquid (the dispersed phase) suspended in the other liquid (the continuous phase). The dispersion will exhibit a distribution of drop diameters d, often characterized by the volume to surface area average diameter or Sauter mean drop diameter. The term emulsion generally refers to a liquid-liquid dispersion with a dispersed-phase mean drop diameter on the order of 1 pm or less. 

Interfacial Area The mass-transfer efficiency of most extraction devices is proportional to the area available for mass transfer (neglecting any axial mixing effects). As discussed in Liquid-Liquid Dispersion Fundamentals, for the general case where the dispersed phase travels through the column as drops, an average liquid-hquid interfacial area can be calculated from the Sauter mean drop diameter and dispersed-phase holdup ... 

Decanter drop diameter > 100 pm feed concentration >2% v/v. Related topics where decanters are used include three phase separation, see gas-liquid-liquid separation, see Section 5.4 solvent extraction, see Section 4.10 azeotropic and extractive distillation, see Section 4.2 liquid-liquid CSTR reactions (such as alkylation), see Section 6.29. 

Liquid-Uquid Holdup volume fraction dispersed liquid 0.01-0.5. Typical drop diameter is 150 pm Power input 0.2-3 kW/m. Related topic solvent extraction. Sections 4.10 and 1.6.2. 

The 7/method was successfully applied to study a variety of drop-on-fiber systems [20,24] and also to characterize the wetting behavior of (carbon) fiber-polymer melt systems [25-27]. Fig. 13 shows exemplarily a drop of polyimide (PI, Aurum PD 400) melt on a carbon fiber (Toray T700SQ at 420 °C in air atmosphere together with the extracted drop profile. The carbon fibers studied have diameters of approx. 7 pm. 

In the processing of instant coffee, extract particles (diameter of 4 x 10 m) drop through air at a temperature of 150°C. If the extract density is 1030 kg/m, what is the terminal velocity of the particles ... 

In the manual scheme, a number of coordinate points, approximately 8 to 10, on the periphery of the drop are extracted by a cursor on a video screen (45). An average drop diameter is then calculated by finding a circle which best fits the selected points, via a least-squares curve fitting method. The ADSA-D program calculates the contact angle, based on the drop diameter and the other required input parameters. 

Equations (10.73) and (10.74) can be used with any consistent set of units.] The drop diameter corresponding to the above values is = 2dj. The value of a to be used is intennediate between that for the binaiy solvent pair and the equilibrium value for the extracting system if that can be estimated (data are scarce). Equations (10,73) and (10.74) are recommended for sieve-tray design, but if the resulting velocity calculates to be less than 0.1 m/s, Vq should be set at least at from 0.1 to 0.IS m/s and the drop diameter should be estimated from Fig. 10.46. 

Interfacial Contact Area and Approach to Equilibrium. Experimental extraction cells such as the original Lewis stirred cell (52) are often operated with a flat Hquid—Hquid interface the area of which can easily be measured. In the single-drop apparatus, a regular sequence of drops of known diameter is released through the continuous phase (42). These units are useful for the direct calculation of the mass flux N and hence the mass-transfer coefficient for a given system. 

The nonuniformity of drop dispersions can often be important in extraction. This nonuniformity can lead to axial variation of holdup in a column even though the flow rates and other conditions are held constant. For example, there is a tendency for the smallest drops to remain in a column longer than the larger ones, and thereby to accumulate and lead to a locali2ed increase in holdup. This phenomenon has been studied in reciprocating-plate columns (74). In the process of drop breakup, extremely small secondary drops are often formed (64). These drops, which may be only a few micrometers in diameter, can become entrained in the continuous phase when leaving the contactor. Entrainment can occur weU below the flooding point. 

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