EHD Heat Exchanger and Chemical Reactors
The application of high voltage electric field to enhance the rate of mass transfer in liquid-liquid extraction has been an active subject of investigation for past 25 years. Among the large amount of published work, there have been several review papers
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Chapter 23 EHD BEAT EXCHANGER AND CHEMICAL REACTORS
23.1 Introduction
The application of high voltage electric field to enhance the rate of mass transfer in liquid-liquid extraction has been an active subject of investigation for past 25 years. Among the large amount of published work, there have been several review papers and short articles which have summarized most of the work having been done to date (Thornton, 1968; Scott, 1989; Weatherley, 1992; Ptasinski and Kerkhof, 1992). The general idea of directly using an electric field to improve the performance of mass transfer in liquid-liquid extraction was initially described by Stewart and Thornton (1967). The improvement of interfacial mass transfer may be achieved in several ways due to the additional electrohydrodynamic (EHD) forces on the droplet-continuum interface: (1) reducing the effective interfacial tension; (2) increasing interfacial area for mass transfer and (3) enhancing interfacial disturbance and drop circulation. The basic techniques to achieve electrically enhanced liquid-liquid extraction are briefly summarized in Table 23.1. Although there is so far no industrial scale application of electrically enhanced mass transfer in liquid-liquid extraction (Scott, 1989; Weatherley, 1992), investigations on some industrially related systems have been carried out. For example, extraction of nickel, copper, uranium and rare earths (Bailes, 1977, 1981; Martin et al., 1984; Hund and Lancelot, 1986), and extraction of penicillin G and other products from whole fermentation broths (Millar and Weatherley, 1989; Weatherley et al., 1990) have been reported. Table 23.1 shows that most of the work conducted with a uniform electric field was either confined to the interpretation of total mass transfer performance or restricted to the discrete droplet regime; and all systems selected had low viscosities. In most cases, the mechanisms of electrically enhanced mass transfer were still not clearly understood and the reported results were very much system dependent. On the other hand, two-phase heat transfer enhancement applications by EHD forces are conducted manily for single component cases such as boiling and condensing two-phase flow, where two-phase EHD heat exchangers developed are listed in Table 23.2. In this moment, several industrial scale proto-type heat pumps are tested (Yabe 1995).
A. Castellanos (ed.), Electrohydrodynamics © Springer-Verlag Wien 1998
claa column: 9 em (i.d.), 19 em hilh
Bailea & Thornton (11171)
glua column (coated with polyt!!tllytepe) 5 em i.d., '\5 em ·hi1h multi-drop distributor
glass column; 3.9 em i.d., 120 em high multi-drop diatributor plate with nine mm dia. hola d.c., < 15 kV, ~ 8 •t.age. of statinleu steel rods, 10 em long each coated wtth teflon
glass column. 30 em i.d. d c., 0-36 'kV, electrode: single nonle, 0.6 mm i d.(to H.V.aource) 2 parallel plates, 30 em dia. gap: 5 em,
Kowalski ll Ziolkowski (1981)
Martinet al. (1983)
Yamaguchi et al. (1985)
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