Ind. Eng. Chem. Res. 1995,34, 1394-1403
1394
Experimental Investigation of Electrostatic Dispersion of Nonconductive Fluids into Conductive Fluids Costas Tsouris,* David W. DePaoli, James Q. Feng, and Timothy C. Scott Chemical Technology Division, Oak Ridge National Laboratory , P.O. Box 2008, Oak Ridge, Tennessee 37831-6226
Electrostatic dispersion has been used extensively in many fields including electrostatic printing, paint spraying, crop spraying, and chemical processing. Most of the applications reported to date, however, are limited to spraying fluids of high electrical conductivity into fluids of lower electrical conductivity. Recent attempts on electrostatic spraying of nonconductive fluids into conductive fluids have shown promising results. Here, we report a n experimental investigation of the influence of physical properties of the fluids, nozzle geometry, and operating conditions on the spraying behavior of nonconductive fluids into conductive fluids. Our results show that the experiments are consistent with the theory of electrohydrodynamics. Also, the results provided in this paper can lead to effective nozzle design for gas-liquid and liquid-liquid dispersions for various applications.
Introduction The phenomenon of electrostatic dispersion of one fluid into another was first demonstrated more than two centuries ago (1750) by Abbe Nollet (see Felici, 1959). In recent years, electrostatic dispersion has found important applications in such fields as painting, printing, and agriculture, among others (Bailey, 1984). A particular example of its application in the chemical industry is solvent extraction, where the objective is to enhance the surface area of contact between the solvents and internal mixing within the drops to increase the mass-transfer rate and the separation efficiency. Devices traditionally used to contact two phases make use of mechanical agitation with various types of impellers (e.g., Oldshue and Rushton, 1952) and fluid pulsation through perforated plates installed in column contactors (e.g., Lo et al., 1983). These devices waste a large fraction of the agitation energy in excessive mixing of the continuous phase, which, in column contactors, results in undesirable backmixing flow. Electrically driven devices overcome this problem by providing the energy required for droplet breakup directly at the interface (Scott, 1989). The knowledge that an electrically stressed interface becomes unstable at a critical electric-field strength emitting fine droplets led to designs of electrical devices t o efficiently contact immiscible fluids (Thornton, 1968; Bailes, 1979; Kowalski and Ziolkowski, 1981; Scott and Wham, 1989). The idea behind these devices is to employ electric fields to increase the interfacial area of contact and to induce a coalescence-redispersion cycle t o control the droplet size. Such devices are not currently used to a significant extent in industry, but recent results by Scott and Wham (1989)and Scott et al. (1994) using an emulsion-phase contactor (EPC) prove that electric-field-driven contactors have the potential t o become far more effective than mechanically driven contactors. Another application of electrostatic spraying has recently been suggested in the area of manufacturing of ceramics by Harris et al. (1993). A multiphase electrodispersion precipitation reactor, the electric dispersion reactor (EDR), was developed to synthesize
* Author to whom correspondence
should be addressed.
ultrafine particles for the production of precursor powders of advanced ceramic materials. A pulsed electric field was employed to create micron-size aqueous-phase droplets in nonconductive organic liquids. Species initially dissolved in the organic phase diffused into the aqueous-phase droplet where precipitation reactions and gelation occurred. The EDR produced 0.1-5-pmdiameter silica, alumina, zirconia, yttria, and composite hydrous oxide particles from metal alkoxide and metal salt precursors. All the electrically driven chemical-processingdevices developed to date, including the EPC and EDR, however, can be used only for dispersing conductive fluids in nonconductive media. The goal of the present article is to provide a fundamental understanding which could lead to the development of new devices that allow spraying of nonconductive fluids into conductive ones, so that the applications of electrostatic dispersion can be extended to such areas where dispersion of a nonconductive fluid into a conductive fluid is desirable. In a review article by Bailey (1984), the mechanism of electrostatic spraying is shown to be the result of the interaction between surface charge on a fluid meniscus and an externally applied field. The presence of the electric field drives charge carriers from the bulk of the dispersed liquid to the surface very rapidly. In a nozzle configuration, the interaction of the external field with the surface charge results in a force on the interface pointing outward with respect to the meniscus. The spraying process depends highly on this outward electrostatic force and on physical properties of the liquid such as viscosity, density, and surface tension. Such discussion is referred to as electrostatic spraying of conductive fluids into nonconductive fluids, which, until recently, was believed to be the only successful spraying mode. Recent experiments by Sat0 and co-workers (1979,1980a,b, 1993) and Tsouris et al. (1994) showed that electrostatic spraying of nonconductive fluids into conductive fluids is possible when the nozzle electrode is adequately insulated. Beyond the obvious advantages of increasing the range of applications, another important advantage of dispersing nonconductive fluids into conductive fluids is that it allows high dispersed-phase volume fractions, in contrast to the inverse system, where sparking occurs above a certain volume fraction of the dispersed phase
0888-5885/95/2634-1394$09.00/00 1995 American Chemical Society
Ind. Eng. Chem. Res., Vol. 34, No. 4, 1995 1395
hypodermic needle 1 mm
I Idc high voltage supply I
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Figure 1. Detail of the capillary nozzle of Sat0 et al. (1993). Nozzle i.d. = 0.25 mm, nozzle 0.d. = 0.50 mm.
(Scott et al., 1994). In fact, in the nonconductive-inconductive system, the higher volume fraction of the dispersed phase decreases the conductivity of the medium and thus may facilitate the operation of electrostatic dispersion. This operational property can provide more flexibility in the selection of flow-rate ratios for the continuous and dispersed phases. In their experiments, Sat0 et al. (1993) used a hypodermic needle (0.25-mmi.d. x 0.50-mm OD) as the capillary nozzle. By using a nonconductive glass coating, they insulated the majority of the outside surface of the nozzle from the continuous phase, which is a conductive liquid, leaving 1 mm of the metal nozzle exposed to the surrounding fluid. The geometry of the device by Sato and co-workers is shown in Figure 1.The ground electrode was a circular aluminum plate of 60mm diameter with a 10-mm-diameter hole at the center and of 2-mm thickness. The distance between the tip of the nozzle electrode and the ground electrode was 50 mm. Using this configuration, Sat0 et al. (1993) were able to atomize low-conductivity liquids, such as kerosene, castor oil, and carbon tetrachloride, in distilled water. At low applied voltages (-400 V), they observed regular dripping, whereas at higher voltages (-2000 V), they observed atomization into narrowly distributed micron-size droplets. The physical properties of the liquids were found to play an important role in the atomization process. Sato and co-workers suggested that the nozzle design is the most important factor for successhl atomization of highly insulating nonconductive fluids and that success of the process is based on a nozzle geometry which creates a very intense nonuniform electric field in the vicinity of the nozzle tip. The Mechanism. The mechanism of electrostatic spraying of nonconductive fluids into conductive fluids is discussed in a recent communicationpaper by Tsouris et al. (1994). Here, only a short summary of the mechanism is given. According to the theory of electrohydrodynamics (Lord Rayleigh, 1982; Melcher, 1981; Taylor, 1964; Landau and Lifshitz, 19601, the key to electrostatic spraying is the electric stress on the interface. A component of the force due to the electric stress acts perpendicular to the interface and in the direction from the conductive fluid to the nonconductive fluid. Therefore, in the conductivein-nonconductive case, the force acts outward; whereas in the nonconductive-in-conductivecase, the force acts inward, with respect to the meniscus attached to the nozzle. This difference in the direction of the force is
reflected in pressure measurements made inside the nozzle. A detailed procedure of such measurements is presented in the Results section. Furthermore, in the present study, we discuss experimental investigations of electrostatic spraying of gases, effect of the conductivity of the surrounding phase, effect of the dispersed phase flow rate, and the shape of the fluid interface during electrostatic spraying. Following are a detailed description of the experimental assembly under Materials and Methods; experimental findings on the effect of geometric parameters, physical properties, and operating conditions on the spraying behavior presented under Results; and a short discussion of possible applications.
Materials and Methods The objective of the experiments was to investigate the effects of several parameters involved in the spraying process on the drop size. This objective was pursued by systematically examining the spraying behavior by monitoring electrical current, pressure, and drop size under various geometric configurations and for different fluid systems. The pressure inside the nozzle is monitored by a pressure transducer, the electrical current is read from the meter attached t o the power supply t o which the metal nozzle is connected, and the drop size is obtained from visualization of drops formed a t the tip of the nozzle. Comparisons of the nonconductive-in-conductive system with the conductive-in-nonconductivesystem that has been extensively studied in the past are very helpful in determining the new mechanisms and verifying electrohydrodynamic reasoning. Experiments were conducted to determine the effects of the distance between the nozzle electrode and the ground electrode, the distance between the metal tip and the ceramicinsulation tip of the nozzle, the wall thickness of the ceramic insulation tube, the flow rate of the dispersed fluid, the conductivity of the continuous-phase liquid, the applied voltage, and the electrical current. Experimental Assembly. Figure 2a shows the apparatus for electrostatic spraying. A syringe pump (Razel, Model A-99) is used to drive a nonconductive fluid through a nozzle electrode into distilled water placed in a rectangular glass tank contactor of dimensions 50 mm x 50 mm x 200 mm. The nozzle electrode is connected t o a high-voltage power supply (Bertan Associates, Inc., Series 225) and is insulated by a ceramic tube. The ground electrode is a metal rod of approximately 3 mm in diameter placed horizontally a t a variable distance from the end of the nozzle electrode. A high-speed imaging system (Kodak, Ektapro Intensified Imager; maximum speed, 12 000 frames per second) is used t o visualize drops generated at the tip of the nozzle. The imaging system is connected to a video recorder (Panasonic, AG 1960 pro-line), a monitor (Audiotronics, 14VM9391, and a printer (Mitsubishi, Video copy processor). Also shown in Figure 2a is a pressure transducer (ENDEVCO Z, Model 8510B-1) which operates in the range of 0-1 psig and is connected to a data acquisition system. The high-voltage power supply operates in a current range of 0-0.3 mA and provides digital readings of the applied voltage and electrical current. Details of the geometry of the nozzle are shown in Figure 2b. The major difference between this geometry and the geometry of the device by Sato and co-workers (Figure 1)is that the inside conductive tube of the nozzle of Figure 2b is allowed to move in and out of the insulating tube. In contrast, the distance
1396 Ind. Eng. Chem. Res., Vol. 34,No. 4, 1995 Nonconductive
Distilled Water
Figure 2. (a) Experimental assembly for electrostatic spraying. (b) Nozzle geometry. Nozzle i.d. = 0.125-1 mm, nozzle 0.d. = 0.8-1.6 mm; insulation i.d. = 0.8-1.6 mm, insulation 0.d. = 1.6-3.2 mm; dispersed-phase flow rate = 0.1-1 mumin. Table 1. Physical Properties ~
~~
interfacial density d i p tension conductivity (@*- @water) with water @mho/cm) substance (g/cm3) viscosity (cP) (dyn/cm) OcSlcm) water hexane TCE air ethanol nitrogen
-0.34 0.46 -1.00 -0.19 -1.00
1.00 0.31 0.60 0.002 1.40 0.002
37.5 37.0 72.0 (-air) 22.3
0.3-13 10-12 10-2 1.5
a e* density for a substance other than water. between the needle end and the glass end of the device by Sat0 and co-workers was fured at 1mm. The metal nozzle is constructed of electropolished and electrolytically cut capillary tubing obtained from Valco Instruments (tubing kits TlON5D, TlONlOD, and TlON15D). Different inside and outside diameters for both the nozzle electrode and the ceramic insulation tube have been tested successfully. It has been observed that with smaller diameter nozzles electrostatic spraying occurs at a lower applied voltage. Experiments were conducted with different dimensions of the stainless steel nozzle electrode, varying in inside diameter from 0.125 to 0.5 mm and in outside diameter from 0.8 to 1.6 mm, and for the ceramic insulation tube, varying in inside diameter from 0.8 to 1.6 mm and in outside diameter from 1.6 to 3.2 mm. No additional insulation or sealant was applied between the nozzle electrode and the ceramic insulation, and therefore, the distance between the tip of the metal and the tip of the ceramic could be easily adjusted. The outside diameter of the ceramic insulation was used for calibration of drop or bubble size measurements. The geometry shown in Figure 2a is used for electrostatic dispersion of fluids heavier than the continuous phase, although spraying of lighter fluids is also possible. In the case of spraying lighter fluids, the nozzle is introduced at the bottom of the tank. Materials. The sample fluids that have been used in this study are trichloroethylene (TCE) (Fisher), hexane isomers (Fisher), air in distilled water, distilled water in air, and nitrogen in ethanol (95%)-water (5%). The physical properties of these fluids are given in Table 1. The interfacial tension and conductivity measurements of water were obtained in our laboratory using a Fisher Autotensiomat and a conductivity m'eter from The London Company (CDM 2e). The conductivity of TCE was measured in the laboratories of Scientifica
Figure 3. Electrostatic dispersion of TCE in water.
(Conductivity Meter, Model 627), manufacturer of lowconductivity meters. All the other properties were obtained from the literature (e.g., CRC Handbook of Chemistry and Physics). The flow rate of the dispersed fluid was maintained constant for the duration of each experiment but varied from 0.1 to 1mumin for different experiments.
Results The results of a typical experiment of electrostatic spraying of TCE in deionized water (conductivity = 0.3 pmhokm) are shown in Figure 3. TCE, introduced through the nozzle, is electrostatically sprayed into micron-size droplets which have very long residence times, as visually appears in the turbidity of the water. The purpose of Figure 3 is to demonstrate electrostatic spraying of a nonconductive fluid into a conductive fluid. The conditions of this experiment, however, result in a very fine dispersion which requires special equipment, currently not available in our laboratory, for visualization of the spraying process and size measurements. Different conditions have to be employed in order to study the effect of different geometric configurationsand operating parameters on such quantities as drop or
Ind. Eng. Chem. Res., Vol. 34, No. 4, 1995 1397 Applied voltage-0 V
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Figure 4. Pressure measurements during drop formation of TCE in distilled water. Nozzle i.d. = 0.25 mm, nozzle 0.d. = 0.8 mm; insulation i.d. = 0.8 mm, insulation 0.d. = 1.6 mm; flow rate = 0.1 mumin. (a) 0 V, (b) 100 V, (c) 200 V.
bubble size and electrical current or energy consumption. In the following experiments, voltages lower than the one used in the experiment of Figure 3 are applied so that larger drops are produced which allow detailed measurements of the parameters involved in the spraying process. The reason for this is that larger drops move fast through the continuous phase and do not accumulate a t the nozzle-tip area t o disturb the measurements of subsequent drops. Pressure Measurements. The electrohydrodynamic theory predicts a difference in pressure inside the nozzle between the nonconductive-in-conductive and conductive-in-nonconductive spraying systems. This prediction was confirmed by Tsouris et al. (1994) with pressure measurements of the two contrary systems. Shown in Figure 4 are the results of pressure measurements over a period of 100 s during drop formation of TCE in distilled water (conductivity = 2.5 pmho/cm) for different values of the applied voltage. In these experiments, the tip of the metal nozzle and the tip of the ceramic tube are at the same level. The applied voltage is 0 V in Figure 4a, 100 V in Figure 4b, and 200 V in Figure 4c. The pressure data show an oscillatory behavior where each maximum corresponds t o a hemispherical geometry of a growing drop hanging at the nozzle tip, and each minimum corresponds to the release of a drop from the nozzle. It should be clarified here that, when the metal nozzle is extended out of the insulation tube, the drop wets only the metal tip. On the other hand, when the metal tip is at the same level with or hidden inside the insulation tube, the drop wets the tip of the ceramic tube. The frequency of the pressure data is the same as the frequency of drop release, and therefore, one can estimate the average drop size from the flow rate of the drop phase and the frequency of drop release. In the experiments reported here, the drop size is also determined from pictures of the drops. Figure 4 shows that the frequency of drop release increases and the drop size decreases with increasing applied voltage. Also, the average pressure and electrical current increase at higher voltages. These observations are more apparent in Figure 5, where variations of the current and average pressure are presented with the applied voltage. Each pressure data point in Figure 5 is the averaged value of measure-
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ments obtained over a time period of 100 s with a sampling frequency of 10 Hz. A comparison between pressure measurements for nonconductive-in-conductive and conductive-in-nonconductive systems (Tsouris et al., 1994) showed that the pressure, in the case of the conductive-in-nonconductive system (distilled water in hexane), decreases slightly with the voltage as a result of the outward force on the meniscus interface, whereas, in the nonconductive-inconductive case (TCE in distilled water), the opposite behavior is observed. In the latter case, the pressure increases sharply with applied voltage (see Figure 51, revealing that an inward force is applied from the conductive fluid surrounding the nozzle toward the nonconductive fluid inside the nozzle. These observations are, therefore, consistent with the electrohydrodynamic theory.
1398 Ind. Eng. Chem. Res., Vol. 34, No. 4,1995
Distance between the End of the Nozzle and That of the Insulation Tube. Figure 6 shows the behavior of the spraying system when the distance between the metal nozzle tip and the ceramic insulation tip is varied. By comparison, the case of the nozzle tip receding inside the ceramic tube, i.e., 1 mm from the tip of the ceramic tube, exhibits the best performance. From Figure 6a, it is seen that the pressure increases when the nozzle tip is moved inside the insulation. Electrical current measurements in Figure 6b show that the electrical current increases rapidly when the nozzle tip is exposed to the surrounding distilled water. When the current exceeds 0.3 d, the experiment is automatically interrupted, due to the power supply cutoff, which accounts for the limited data points in the cases of inadequate insulation. Corresponding drop size measurements to the three situations examined in this set of experiments are shown in Figure 6c. Thus, of the configurations tested, the most desirable setup for electrostatic spraying is when the nozzle tip is hidden somewhere (-1 mm in the present case) inside the ceramic insulation tube. Apparently, in this case, the electrical current is the lowest of the three cases and the drop size the smallest at the same applied voltage; therefore, the input energy in this case is used most effectively. As discussed later, however, there is a practical limitation to the distance between the nozzle and insulation tips. Thickness of the Insulation Tube. From an electrostatic point of view, the thickness of a perfect insulation tube should have no effect on the spraying behavior. In Figure 7, however, an effect of the insulation thickness is observed due to wetting of the insulating wall by the meniscus. The metal nozzle with the ceramic insulation tube of 0.8-mm i.d. x 1.6-mm 0.d. was inserted in a second ceramic tube of 1.6-mm i.d. x 3.2-mm 0.d. to form a double insulation wall around the metal nozzle. The tip of the metal nozzle in this set of experiments is placed at the same level with the tip of the insulation. In the experiments of Figure 7, the tips of both inner and outer insulation tubes were wetted by the drop. The result of the wetting is that the size of the drops, formed in the absence of applied voltage, is slightly larger for double insulation than for single insulation. In Figure 7a, decrease in the pressure is observed when the double insulation is used due to lower curvature of the meniscus. No effect on the current is shown in Figure 7b, while in Figure 7c the drop size is shown to be larger in the double-insulation case. The differences shown in the data of Figure 7c between single-wall and double-wall insulation are attributed to the larger drop size produced in the doubleinsulation case due to the wetting of the total combined ceramic tip by the drop.
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Distance between Nozzle and Ground Electrodes. The effect of the distance between the nozzle and the ground electrodes is shown in Figure 8a for the pressure, Figure 8b for the current, and Figure 8c for the drop size. Only the pressure and the current in Figure 8a and 8b, respectively, show slightly higher values for the shorter distance, while there is no significant difference in the drop size. On the contrary, in the case of the inverse system, i.e., conductive-innonconductive, the distance between the nozzle and the ground can significantly affect the behavior of electrostatic spraying (e.g., Bailey, 1988). The reason for the different behavior is that the surrounding liquid in the nonconductive-in-conductive case, because of its high conductivity, renders every part at nearly the same potential as imposed by the connected electrode. A
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Applied Voltage (kV) Figure 6. Effect of distance between the metal nozzle tip and the ceramic-insulation tip on (a)pressure, (b) current, and (c) drop size. System: TCE in distilled water; nozzle i.d. = 0.5 mm, nozzle 0.d. = 0.8 mm; insulation i.d. = 0.8 mm, insulation 0.d. = 1.6 mm; flow rate = 0.5 mlimin.
Ind. Eng. Chem. Res., Vol. 34,No. 4,1995 1399 5 +doublr
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1402 Ind. Eng. Chem. Res., Vol. 34,No. 4, 1995
electrostatic spraying. Higher voltage is required to deform the drop-insulation interface and come in contact with the metal electrode. Because of the higher electric potential across the interface, as soon as the surrounding phase comes in contact with the nozzle, sparking occurs which instantaneously destroys the potential and prevents electrostatic spraying (Figure 150. Thus, there is a limit as to how far inside the insulation tube the nozzle can be located and still allow electrostatic spraying. This limit depends upon the physical properties of the fluids (e.g., interfacial tension, viscosities, and densities) and the geometry of the device (e.g., inside diameter). Spraying of Nitrogen in Ethanol. Electrostatic spraying of air in distilled water has been presented in Figure 9. In this section, electrostatic dispersion of a different system, nitrogen in ethanol, is discussed. Pictures of bubbles taken during this experiment are shown in Figure 16. The surrounding phase is 95% ethanol and 5% water and has a conductivity value similar to that of the distilled water used in this study. This system behaves similarly to the air-in-water system.
Discussion
Figure 15. Fluid interface visualization during electrostatic spraying. System: TCE in distilled water; nozzle i.d. = 0.8 mm, nozzle 0.d. = 1.6 mm; insulation i.d. = 1.6 mm, insulation 0.d. = 3.2 mm; applied voltage = 1.0 kV. (a) No field, nozzle 1mm inside; (b) low applied voltage; (c) intermediate applied voltage, drop mode; (d) high applied voltage, spraying mode; (e) higher flow rate; (0 sparking, nozzle >2 mm inside.
to the tendency of the sprayed phase (TCE in this case) to wet the internal surface of the tube. The large drops attached at the tip of the glass insulation are a result of TCE wetting the glass surface. A hysteresis in this phenomenon was noted when the applied voltage decreased. It was observed that the surrounding conductive phase remained in contact with the metal electrode as the applied voltage decreased to a certain limit, VI -= Vu. This hysteresis happens because the voltage required to deform the large drop-insulation interface is greater than that necessary to maintain dispersion in the smaller interface case. Moving the metal nozzle inside the insulation tube by more than 2 mm was found to create problems on
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Significant differences in the behavior of electrostatic spraying of the two different systems, i.e., conductivein-nonconductiveand nonconductive-in-conductive,have been observed, both in pictures of drops during release and in pressure measurements (Tsouris et al., 1994). For the conductive-in-nonconductivesystem (e.g.,water in air), the drop at the nozzle is elongated and very fine drops are released from its tip toward the second electrode. This behavior is a result of a strong outward force applied at the interface (see also Sample and Bollini, 1972). At higher applied voltages,jetting occurs in various directions as the tip of the attached drop shifts alternately from one side of the nozzle to the other (Zeleny, 1915; Cloupeau and Prunet-Foch, 1989). In the inverse case, however, inward forces directed from the conductive to the nonconductive fluid act at the tip of the nozzle forcing the release of fine drops or bubbles at the nozzle-tip area. The higher the electric field, the stronger the inward forces become and the smaller the drops that are generated. Inward forces are stronger near the wall of the metal nozzle, where the thickness of the attached nonconductive drop or bubble is minimum; therefore, drop release occurs at the center of the nozzle, right at the tip, as a result of a pinch-off action. The key to electrostatic spraying is the electric stress on the interface. A component of the force due to the electric stress acts perpendicularly to the interface and in the direction from the conductive fluid to the nonconductive fluid. Therefore, in the conductive-in-nonconductive case, the force acts outward, whereas, in the nonconductive-in-conductivecase, the force acts inward,
600 V
1100
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Figure 16. Electrostatic spraying of nitrogen in ethanol: nozzle i.d. = 0.125 mm, nozzle 0.d. = 1.6 mm; insulation i.d. = 1.6 mm, insulation 0.d. = 3.2 mm.
Ind. Eng. Chem. Res., Vol. 34, No. 4, 1995 1403 with respect to the meniscus. It has been shown here that, whether the force acts outward or inward, electrostatic spraying is possible if a strong enough electrostatic field is maintained. There are differences, however, in the spraying behavior of the two cases which originate from the force direction on the interface. These differences are seen in pictures of drop release from the nozzle and in pressure, current, and drop-size measurements. Furthermore, it has been observed that, during the spraying process, the conductive surrounding phase was continuously in contact with the metal interface, and drop spraying occurred at the center of the nozzle. When the metal nozzle is located far enough inside the insulation tube, higher applied voltage is required to create electrostatic spraying. Under such conditions, the surrounding phase jets inside the nozzle causing sparking. The same behavior is observed when the surrounding phase is highly conductive. Finally, it should be pointed out here that more work is needed to correlate the size of the emitted drops or bubbles with the pertinent parameters of the system. For this purpose, a dimensional analysis utilizing a sufficient number of experimental data from various chemical systems and geometric configurations is required.
Summary The work presented here demonstrates electrostatic spraying of nonconductive fluids in distilled water. This mode of electrostatic spraying is complementary to the well-known electrostatic spraying of conductive fluids in nonconductive fluids and may have diverse applications in industry. The importance of many parameters involved in the electrostatic spraying process is experimentally examined. A nozzle design is also suggested to produce electrostatic dispersions of nonconductive fluids in highly conductive water. The presented results and conclusions can be used for proper design of spraying nozzle systems in applications of multiphase processing. Such applications can be found in gasliquid processes (e.g., chlorination and ozonation of drinking water and wastewaters in environmentalengineering systems, oxygenation in bioprocessing systems, and distillation in the chemical industry), liquidliquid processes (e.g., extraction in metallurgy and chemical industry), and liquid-solid processess (e.g., manufacturing of materials).
Acknowledgment Funding provided by the Division of Chemical Sciences, U.S. Department of Energy, under Contract DEAC05-840R21400 with Martin Marietta Energy Systems, Inc., is gratefully acknowledged. This research was supported in part by an appointment t o the Oak Ridge National Laboratory (ORNL) Postdoctoral Research Associates Program, administered jointly by ORNL and Oak Ridge Associated Universities.
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