We have developed a novel fabrication technique for a passive, continuous flow micromixer with laminar flow. The device is made by welding thin thermoplastic sheets using a simple manufacturing procedure which reduces the total cost of the device, and enables frequent changes to the design as necessary. Two types of mixers were made, one with obstacles in the mixing channel to induce the forming of vortices, and the other having serpentine design. For both mixer designs we made a range of mixing chamber sizes to examine the efficiency of the mixing process in respect to available mixing length. In experiments we used two different colored water solutions to inject at the device inlets. The flow rate of the fluids was controlled by Cole Parmer Instruments syringe pump and the observed colored patterns are recorded using Digital Blue™ QX5 microscope. As the flow rate was changed in experiments from 0.01 to 100 microliter/min, the mixing was accomplished further down the channel and in some cases was not completed within the mixing chamber. However the relation between mixing length and flow rate (Reynolds number) is not linear and after certain value of Reynolds number the mixing is completed at a shorter distance from the inlets then expected. Our experimental results with larger devices show this non-linearity, while for the devices of smaller size that was not observed.

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