.A non-intrusive electrical impedance-based sensor is developed for measurement of local void fraction in air-water adiabatic flow through rectangular microchannels. Measurement of the void fraction in microchannels is essential for the formulation of two-phase flow heat transfer and pressure drop correlations, and may enable real-time flow regime control and performance prediction in the thermal regulation of high-heat-flux devices. The impedance response of the sensor to a range of flow regimes is first investigated in a crosswise (transverse) configuration with two aligned electrodes flush-mounted on opposing microchannel walls. Numerical simulations performed on a multi-phase domain constructed from three-dimensional reconstruction of experimentally observed phase boundaries along with the corresponding experimental results serve to establish the relationship between void fraction and dimensionless impedance for this geometric configuration. A reduced-order analytical model developed based on an assumption of stratified gas-liquid flow allows ready extension of these calibration results to different working fluids of interest. An alternative streamwise sensor configuration is investigated with two electrodes flush-mounted along a single wall in the flow direction in view of its potentially simpler practical implementation in arrays of microchannels. It is shown that a correlation between time-averaged impedance and void fraction can be established for this alternative configuration as well.


microchannel, two-phase flow, void fraction, impedance meter, sensor design

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P. Valiorgue, S. N. Ritchey, J. A. Weibel and S. V. Garimella, “Design of a Non-intrusive Electrical Impedance-Based Void Fraction Sensor for Microchannel Two-Phase Flows,” Measurement Science and Technology Vol. 25, 095301, 2014.