The formation of single charged drops in a uniform electric field is studied as a fundamental of "electrostatic liquid extraction". Theoretical equations are derived for the volume and the electric charge of the drop formed at the tip of an electrified nozzle that protrudes from one of a pair of parallel plate electrodes. The experimental measurements were performed in atmosphere by use of three nozzles (0.1, 0.15 and 0.26 cm O.D.) in an electric field range of 0-6 x 105 V-m"1.It has been clarified theoretically and experimentally that drop volume decreases remarkably with increase of electric field strength and also with increase of protrusion length (0-1.0 cm) of the nozzle. The theoretical equation gives a somewhat larger drop volume than that obtained experimentally, but it represents well the effect of protrusion length on volume. Experimental data of drop charge are in good agreement with the theoretical predictions whenthe nozzle protrusion length is relatively short.Although some deviations are found between the experimental and the theoretical values, the behavior of single charged drop formation is predicted by the theoretical equations presented.

The invisible boundary was found in a highpressure region which is not classified by either vaporliquid or liquid-liquid coexistence region from the phase equilibrium measurement for the methanolethylene system up to the critical point. 4) Ohgaki, K., T. Nakatani, T. Saito and T. Katayama: J. Chem. Eng. Japan, 15, 91 (1982).[Pa] 5) Ohgaki, K., H. Nishii and T. Katayama: J. Chem. Eng. Japan, [Pa] 16, 72 (1983 Formation of single drops in a non-uniform electric field is studied for water drops in the atmosphere and in three kinds of dielectric liquids. Theoretical equations are derived for the volumeand the electric charge of the formed drop and corresponding experiments were performed in a range of applied electric potential of 0-7.5 kV, It was clarified that measured drop volumes agree well with theoretical values for systems of liquid-gas and liquid-liquid. The experimental drop charges are not satisfactorily represented by theoretical analysis, but are well evaluated by a semi-empirical equation presented here.

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Mass transfer of iodine from single charged drops of aqueous iodine solution into a continuous phase of cyclohexane was measured during the overall process of formation, free fall and coalescence of the drops in a range of uniform electric field strength up to 2.4 kV/cm. The total amount of iodine transferred was separated into that during drop formation and that during the subsequent stages. Each mass transfer mechanism during the formation and the free fall of drops in the electric field was investigated with theoretical and empirical equations in the literature, which were obtained in the absence of an electric field.The mechanismof mass transfer during the formation of the charged drops in the presence of an electric field and that during free fall of the drops are the same as those obtained in the absence of an electric field. The enhancement of mass transfer obtained in the electric field is due to the increased effective inter facial area per volume of dispersed phase and to the increased moving velocity of the drops caused by applying the electric field.

Stewart and Thornton5] proposed an electrostatic liquid-liquid extractor in which a larger inter facial area of liquid drops and a higher degree of turbulence within and around the drops were produced by applying an electric field. Recently, theoretical and experimental studies have been performed for formation of single charged drops in dielectric liquids in the presence of a uniform electric field7) and for mass transfer rates between the drops and the surroundings.1'T he present study was undertaken to observe the terminal velocity of single charged drops in the electric field, which is an important factor for study of mass transfer rates in the extractor, and to provide basic information for practical design of the extractor.