Chemical reactors with micromixing of liquids play an important role in the chemical engineering process leading to new materials with an improved functional response. We show that the liquids injection conditions correspondent to low Damkohler numbers may turn from the common liquid phase to unusual biphasic liquid vapour fluid flow due to the cavitation phenomenon. We propose in-situ physical measurements of the cavitation threshold in the exocentric T-mixer using light scattering method. Numerical calculations support the assignment to cavitation and show its critical relation to the T-mixer geometry. (C) 2017 Elsevier B.V. All rights, reserved.