Monitoring the glycerol concentration in aqueous glycerol solutions using a micromachined flow sensor

We present a measurement setup to monitor the glycerol concentration in aqueous glycerol solutions. The setup comprises a micromachined thermal flow sensor, a piezoelectric micropump, a well-defined flow channel, a differential pressure sensor, and a temperature controller for a constant setup temperature. The micropump establishes circulation with a constant pressure difference between in- and outlet of the channel ensuring a flow rate in the closed-loop system that is strictly related to the viscosity and, equivalently, to the glycerol concentration. A calorimetric flow sensor operating in the constant over-temperature mode measures the flow rate from which the glycerol concentration can be deduced. The overall system design was supported by FEM simulations. Finally, we report on measurement results which confirm good agreement between theory and experiment.