in the bubble changed continuously by mass transfer. Consider the bubbles shown in the simplified schematic diagram of Fig. 17-1. These bubbles enter with a composition y\ pass up through a liquid of composition Xj and leave with a composition yf0. Using a simplified expression for the instantaneous mass transfer to one of the bubbles,

where G = mois of gas in bubble y1 = mol fraction of component in bubble ye = vapor in equilibrium with liquid P - total pressure

Kg — over-all mass-transfer coefficient, (mols)/(unit time) (unit pressure difference) (unit interfacial surface) a « interfacial area of bubble 6 = contact time of bubble with liquid Assuming G} P, yej and K0a are constant, this equation can be integrated to give

Murphree applied the relation to the whole plate, assuming that conditions were the same at all points. In this case (G/6) is replaced by the vapor rate, and a becomes the average total interfacial area of all the bubbles on a plate at any instant. This equation can be rearranged to where m =

PKQaB

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