Microreactors are basic components of microfluidic systems for chemical and biochemical applications and the large area-to-volume ratio of micro-reactors enables a higher yield and selectivity than conventionally designed processes. To take advantage of the full potential of this ambitious technology, a fundamental understanding of the transport processes on the relevant time and length scales is necessary. Besides the approach of using commercial CFD programs for numerical flow visualization, the microscale fluid flow visualization is an important tool for acquiring localized flow information within these microreactors. To get a deeper insight the mixing characteristic of different T-shaped micro mixers with rectangular cross sections (dimensions: 100–400 micron) has been investigated by means of the non-invasive measurement techniques micro-Laser induced fluorescence (micro-LIF) and micro-Particle Image Velocimetry (micro-PIV). The analysis of the concentration fields proves that with a higher Re a stretching and thinning of liquid lamellae (vortex generation) occurs, causing an enlarged interfacial surface area and consequently leading to a better mixing performance by diffusion. The analysis of the velocity fields shows further the existence of a three dimensional flow in the entrance region of the mixing channel of a T-shaped micro mixer.

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