Operational Limits of Suspension Flows through Sudden Contractions

In many microfluidic MEMS (Micro Electromechanical Systems) especially in μTAS (micro Total Analysis Systems) suspensions of small particles are transported from relatively large chambers into small channels. The sudden contractions at the entrance to these channels are critical flow regions where high shear occurs in the fluid. Even very small particles at low concentrations have been observed to accumulate in these regions where they clog the channel inlet occasionally after a short period of time. The operational limitations for threedimensional suspension flows are examined using dimensional analysis. Thus empirical relations based upon experimental results can be established between the parameters involved in this fluid mechanical problem such as shear rate, particle size and concentration, size and number of sudden contractions, and the time scale of clogging.