Estimation of mixing fields in micromixers and microreactors by visualization method using methylene blue solution

During the development of micromixers and microreactors, it is important to assess the concentration field and mixing status in their microchannels. Therefore, this study establishes a visualization method for evaluating the concentration field using images of dilution of a methylene blue solution with water. Noted that the original methylene blue solution is deep blue before it is mixed with water; it becomes paler once it is diluted, as observed against a white background. Because the methylene blue concentration has a highly reliable relationship with the saturation of the captured color, the local methylene blue concentration can be determined on the basis of a calibration result obtained in advance. The saturation value is affected not only by the concentration but also by the optical effect of the channel walls. Therefore, we established a method of eliminating the channel wall effect. As a trial, we estimated the concentration field in our novel microreactor using the proposed visualization method and estimated the mixing status in the microchannel. We showed that the proposed visualization method effectively estimated the concentration field and mixing status in micromixers and microreactors.