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Natural convection cells accompanying liquid-liquid extraction
Natural convection cells accompanying
liquid-liquid extraction
(&caved 9 June 1961) a flat 65 x 85 mm mterface between two hqmd phases at room temperature The lower phase, 15 mm thick, consists of a solution of acetic acid 111 ethylene glycol Ethyl acetate forms the 17 mm thick upper phase. The ternary system used here IS of Type I It is not subiected to any form of forced convection durmg the tests.
THE TRADITIONAL descrlptlon of mass transfer m hqmdhqmd extraction uses a two film model Although the two-film theory is adequate for pre&ction of transfer rates m many ternary systems, a number of exceptions have been documented [l] The latter systems exhibited abnormally high rates that could not be explamed on the basis of pure molecular diffusion It was found later that the high rates were caused by mterfacral turbulence spontaneous agitation of the interface between two uneqmhbrated hqmd phases Theoretrcal treatment of the phenomenon was lackmg until recently when STERNLINCand &RIVEN formulated their theory of organized mterfaclal motion m a flat mterface Then lmagmatlve paper [2] recerved wide attention, and the Colburn Award of the American Instltutc of Chemmal Engmeers was granted to these authors as a result STERNLING and SCRIVEN predict that spontaneous mterfaeml flows can occur orgamzed m a cellular pattern. The basic umt of flow IS a roll cell within which hqmd is circulatmg. The roll cells are presumed to be analogous to B~NARD cells for heat transfer which are exhibited by an unconfined, honzontal, thm layer of pure hqmd heated proved the existence of heat transfer from below BERNARD cellular convection by stdl photography [3] Interfaclal turbulence has been observed by a large number of investigators In all cases but one the phenomenon was found to be a dlsorgamzed and chaotic process Recently LINDE [4] photographed the Interface of the system rsoamyl alcohol-sodunn cetyl sulphate-water m profile and was able to record a single roll cell with a wave length of about 1’7 mm
The Sternlmg-f&riven theory predicts that this system should exhibit roll cells. Fig 1 proves the existence of a network of polygonal cells on the Interface &self An analysrs of the schheren motion pictures mhcates that, m the heavy phase, hqmdrrses in the centre of these polygonal cells, reaches the interface, and flows radially outward to smk down at the cell boundaries I’olygonal cells are found to be either stationary, occupying a fixed posrtion, or propagating across the mterface Both types increase their size with tune, m accordance with theory Average cell size ranges from 0 04 to 0 14 cm These sizes are urlthm 50 per cent of the pre&cted roll cell wave lengths. As time passes the cells not only increase their size but also change to elongated stripes which appear m clusters as shown m Erg 2. After a long tune this pattern evolves mto slow-movmg, mdely spaced concentrmnpples (Fig 3) These become famter and famter and finally drsappear as the system approaches eqmhbrmm. Interfaclal actlvlty has been observed to last as long as 72 hr. Patterns sumlar to Figs. I and 2 were observed by BBNARDfor heat transfer The apples 111Fig. 3 however are unexpected either from the Sternhng-Scnven theory or from previous observations Expernnental work in this study is contmumg and wdl be reported m due tune.
The obIect of the expernnental work described herem IS to mvestlgate the existence and characterrstlcs of cellular motion during mass transfer
E I du Pant de Nemours and Company New Johnaonvalle, Tennessee
In the present study mterfacial activity is recorded by motion picture and stall photography usmg the Schheren t-chmque The cameras are anned straight down vlewmg
Department of Chemzstry and Chemwal Engwwenng Unaversaty of Zllanozs ALUF ORELL Urbana, Zllznozs J W WES~VATER
REFERENCES [I]
LEWIS J
[2]
STERNLINC C V
[3]
B$N~RD H
[4]
LINDE H
B
Ch.
En@& Sex. 1954 8 230. and SCRI~ENL
E. A I Ch.E. Jowtwl
ZZen.gen Sn. pur. appl
1939 11 1281, 1399
Fe&-, SaJen, Anstnehmatfel 1958 60 828.
127
1959 5 514
liquid-liquid extraction
(&caved 9 June 1961) a flat 65 x 85 mm mterface between two hqmd phases at room temperature The lower phase, 15 mm thick, consists of a solution of acetic acid 111 ethylene glycol Ethyl acetate forms the 17 mm thick upper phase. The ternary system used here IS of Type I It is not subiected to any form of forced convection durmg the tests.
THE TRADITIONAL descrlptlon of mass transfer m hqmdhqmd extraction uses a two film model Although the two-film theory is adequate for pre&ction of transfer rates m many ternary systems, a number of exceptions have been documented [l] The latter systems exhibited abnormally high rates that could not be explamed on the basis of pure molecular diffusion It was found later that the high rates were caused by mterfacral turbulence spontaneous agitation of the interface between two uneqmhbrated hqmd phases Theoretrcal treatment of the phenomenon was lackmg until recently when STERNLINCand &RIVEN formulated their theory of organized mterfaclal motion m a flat mterface Then lmagmatlve paper [2] recerved wide attention, and the Colburn Award of the American Instltutc of Chemmal Engmeers was granted to these authors as a result STERNLING and SCRIVEN predict that spontaneous mterfaeml flows can occur orgamzed m a cellular pattern. The basic umt of flow IS a roll cell within which hqmd is circulatmg. The roll cells are presumed to be analogous to B~NARD cells for heat transfer which are exhibited by an unconfined, honzontal, thm layer of pure hqmd heated proved the existence of heat transfer from below BERNARD cellular convection by stdl photography [3] Interfaclal turbulence has been observed by a large number of investigators In all cases but one the phenomenon was found to be a dlsorgamzed and chaotic process Recently LINDE [4] photographed the Interface of the system rsoamyl alcohol-sodunn cetyl sulphate-water m profile and was able to record a single roll cell with a wave length of about 1’7 mm
The Sternlmg-f&riven theory predicts that this system should exhibit roll cells. Fig 1 proves the existence of a network of polygonal cells on the Interface &self An analysrs of the schheren motion pictures mhcates that, m the heavy phase, hqmdrrses in the centre of these polygonal cells, reaches the interface, and flows radially outward to smk down at the cell boundaries I’olygonal cells are found to be either stationary, occupying a fixed posrtion, or propagating across the mterface Both types increase their size with tune, m accordance with theory Average cell size ranges from 0 04 to 0 14 cm These sizes are urlthm 50 per cent of the pre&cted roll cell wave lengths. As time passes the cells not only increase their size but also change to elongated stripes which appear m clusters as shown m Erg 2. After a long tune this pattern evolves mto slow-movmg, mdely spaced concentrmnpples (Fig 3) These become famter and famter and finally drsappear as the system approaches eqmhbrmm. Interfaclal actlvlty has been observed to last as long as 72 hr. Patterns sumlar to Figs. I and 2 were observed by BBNARDfor heat transfer The apples 111Fig. 3 however are unexpected either from the Sternhng-Scnven theory or from previous observations Expernnental work in this study is contmumg and wdl be reported m due tune.
The obIect of the expernnental work described herem IS to mvestlgate the existence and characterrstlcs of cellular motion during mass transfer
E I du Pant de Nemours and Company New Johnaonvalle, Tennessee
In the present study mterfacial activity is recorded by motion picture and stall photography usmg the Schheren t-chmque The cameras are anned straight down vlewmg
Department of Chemzstry and Chemwal Engwwenng Unaversaty of Zllanozs ALUF ORELL Urbana, Zllznozs J W WES~VATER
REFERENCES [I]
LEWIS J
[2]
STERNLINC C V
[3]
B$N~RD H
[4]
LINDE H
B
Ch.
En@& Sex. 1954 8 230. and SCRI~ENL
E. A I Ch.E. Jowtwl
ZZen.gen Sn. pur. appl
1939 11 1281, 1399
Fe&-, SaJen, Anstnehmatfel 1958 60 828.
127
1959 5 514