Results and discussion
In the segregation experiments, the sampling location was set with a distance away from the inlet of acid injection. In order to guarantee that a well-established micromixing process is achieved throughout the whole reactor, the collection time after acid injection should be determined in advance. The preliminary experiment was performed at a Reynolds number of 12564 in the CTC. It can be seen from Figure 3 that the critical collection time is 120 s after finishing the injection of acid. However, within the range from 90 s to 240 s, the results used to determine the collection time also appear to be acceptable. One can argue that if the collection time is too short, the macromixing has not been fully achieved, thus resulting in little amount of the product being detected at the outlet. On the other hand, if the collection time is too long, the UV result may lose its accuracy since \(I_{3}^{-}\) is very sensitive to light. Therefore, the determination of the critical collection time is crucial for acquiring reliable results. It should be noted that for different operating conditions, the critical collection time may be different within the acceptable range. The following discussion on the micromixing in the TC reactor with two different inner cylinder configurations will be based on the samples collected at the critical collection time determined for the CTC and LTC, respectively.