Mechanically liquid mixing time

Confined flows typically exhibit laminar-flow regimes, i.e. rely on a diffusion mixing mechanism, and consequently are only slowly mixed when the diffusion distance is set too large. For this reason, in view of the potential of microfabrication, many authors pointed to the enhancement of mass transfer that can be achieved on further decreasing the diffusional length scales. By simple correlations based on Fick s law, it is evident that short liquid mixing times in the order of milliseconds should result on decreasing the diffusion distance to a few micrometers. 

P 31] liquid mixing times were calculated based on assuming diffusion as the only mixing mechanism and considering Fick s law which takes into account the diffusion constant and the diffusion distance [114]. 

Liquid residence-time distributions in mechanically stirred gas-liquid-solid operations have apparently not been studied as such. It seems a safe assumption that these systems under normal operating conditions may be considered as perfectly mixed vessels. Van de Vusse (V3) have discussed some aspects of liquid flow in stirred slurry reactors. 

The liquid-phase mixing in a multistage mechanically agitated reactor is best correlated by Eq. (2.31) in the absence of gas flow and by Eq. (2.32) in the presence of gas flow. The mixing time can be estimated from the study of Paca et al. (1976). Experimental work is needed to estimate gas-phase back-mixing. The use of Eq. (2.36) for the calculation of the gas-liquid volumetric mass transfer coefficient in a multistage mechanically agitated column is recommended. 

I f one wishes to measure shorter mixing times on the order of milliseconds, a stopped-flow technique can be employed. This method has been used to ascertain enzyme mechanisms for a number of organic and inorganic chemical reaction.s (Robinson, 1975, 1986). The stopped-flow technique lias not been extensively employed in studying kinetics of solid/liquid inter-iiciioiis (Ikeda el al., 1984a). 

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