Micro-mixer devices, such as the Confined Impinging Jets Reactor (CUR) are currently under study, in particular for precipitation processes of micro- and nano-particles, employed in a variety of applications that include pharmaceuticals, cosmetics, dyes and pesticides. In this work, with the purpose of gaining a better understanding of the main mixing mechanisms occurring in a CIJR, the flow field was studied at four inlet flow rates ranging from Re = 62 to Re = 600. These conditions correspond to regimes with incipient turbulence in the chamber. Micro-Particle Image Velocimetry (microPIV) experiments and Direct Numerical Simulations (DNS) were performed and compared. MicroPIV is an innovative experimental technique that allows measurement of the instantaneous velocity fields in microfluidic devices. The coupled numerical-experimental approach was found to be essential in understanding and explaining the flow behaviour and the development of turbulence, in particular with respect to the important effects of the inlet boundary conditions. Oscillations present in the inlet flow of the device are in fact primarily responsible for the chaotic and turbulent effects in the reactor. These results provide insights that are important in the development of appropriate computational models for this type of micro-reactor or mixers. (C) 2010 Elsevier B.V. All rights reserved.