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The hydrodynamics of two-phase liquid—liquid co-current down-flow in a packed column was investigated using adequate tracer techniques. Emphasis was set upon dispersed phase behaviour and hold-up; the choice of a model which accounts for the experimental results obtained has been discussed.

In a previous work [ J. chem. Technol. Biotechnol. 34B , 121 (1984)] a rapid method was proposed for K L a estimation under growth conditions based on first moment analysis. The response curve of dissolved oxygen concentration is obtained by a sudden change in the stirrer speed while the aeration rate is held constant. The influence of the liquid diffusion film and electrode response on K L a estimation were considered but not the gas phase dynamics because it was assumed that the gas phase remained constant. In the present paper, a new model which considers the influence of the gas phase is proposed. The results show that the gas phase dynamics affect the K L a estimation, and its influence is more pronounced for higher values of K L a and for small aeration rates.

Partial (triangular) decoupling of MIMO systems has been considered in the literature as a way of relaxing the design limitations introduced by diagonal decoupling in non-minimum phase processes. The former strategy allows decoupling a variable of interest without affecting it with non-minimum phase dynamics. However, when right-half plane (RHP) zeros are mainly aligned with this variable, pushing the effect of the RHP zeros to other outputs comes at the cost of great interactions in those variables. This article presents a method to delimit these interactions without degrading significantly the decoupled variable response. To this end, the algorithm shapes the reference signal by means of an auxiliary sliding mode loop.