Effect of electrode configurations on phase equilibria with applied electric fields

Applying an electric field to some boiling binary mixtures has been shown e xperimentally to increase the separation factor by as much as 10%. In this work, an electric field was applied across the interface of boiling mixture s of 2-propanol-water via electrodes located in the vapor and the liquid. T he shape and separation of the electrodes and the strength and polarity of the electric field were altered to investigate their effect on the vapor mo le fraction, the current, and the vapor temperature, The results show that greater voltage differences, in the absence of excessive electrical current , lead to higher concentrations of 2-propanol in the vapor. However. it was found that varying the electrode separation at a given potential differenc e, and thus the electric field strength, has little effect on the vapor com position. The effects of the applied potential difference are reduced with elevated current and under conditions where liquid dynamics such as drippin g, splashing, or jetting provide an opportunity for charge to be transferre d between the electrode in the vapor and the liquid. It is also shown that directing the electric field from the vapor to the liquid produces a lower current, and the effect on the composition is larger. These findings, in co mbination with calculations of the interface charge density, suggest that i mprovements in the separation efficiency achieved by an applied potential d ifference are not due to effects of the electric held in the bulk fluids, b ut rather are induced by charge accumulation at the vapor-liquid interface. (C) 1999 Elsevier Science B.V.