Process definition validating input

Process validation entails firstly the definition of both the critical and non-critical parameters. Qnce they are defined, emphasis can be directed to designing a program to validate these parameters. Some established steps involve the evaluation of process consistency over at least three batches, via the consideration of the processing steps and yield and comparing these with predetermined specifications. Some input parameters that may be considered as critical are temperature, flow rate, and stirring speed, and they are varied and checked against output variables such as yield, purity, and crystallization rate. 

When the stirring rate is decreased, the flow branch is favoured. One could speak of a "forced nucleation" but this term is somehow misleading since the process is purely deterministic and the local perturbation due to the feed is permanent. The validity of the conclusions implies that the input flow is large enough to define the small volume above. This is certainly the case close to ks, where the flow becomes dominant compared to the reaction processes on a macroscopic scale. The transition is shifted to lower values of the flow rate. For the reverse transition at k-j, where the flow is often very small and where the reaction process becomes dominant no definite conclusion can be drawn. We shall now develop these ideas on simple models and show that localized injection of reactants induces effects in qualitative agreement with the experiments. 

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