Global Digital Central Logo Frontiers in Heat and Mass Transfer (FHMT)

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Muthasim Fahmy, Zhifa Sun
Frontiers in Heat and Mass Transfer (FHMT) 2 - 043003 (2011)


A gas-liquid solute transfer process initiated in a closed vessel can exhibit Rayleigh-Bénard-Marangoni (RBM) convection enhanced mass transfer. For short exposure times experimental and theoretical results demonstrate that for deep liquid systems prior to solute penetration across the depth of the fluid, the stability thresholds of the system decreases with time. For thin liquid layers at longer exposure times the mass transfer enhancement under RBM convection can be affected  in two ways: (1) solute penetration to the bottom liquid-solid boundary causing a departure from a penetration type concentration profile; (2) solute penetration to the top gas-solid boundary in the gas phase resulting in deviations of  mass transfer Biot number from the penetration type of Biot number. These two effects have been investigated by imposing non-diffusing boundary conditions in the liquid phase as well as the gas phase. For short contact times, the critical thresholds of convection evaluated via a quasi-static stability analysis under non-diffusing boundary conditions are consistent with those under penetration type concentration profile.  However, at longer exposure times when solute has completely penetrated the entire liquid depth, there can only be a limited period of time when convective instability is possible. Within this period there is a local maximum of convective intensity, thereby opening up the possibility of optimising gas-liquid mass transfer operations with respect to Rayleigh and Marangoni convection. Experimental results supporting these predictions are presented.

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ISSN: 2151-8629