Development of a sensor for liquid film thickness measurements during annular flow in microchannels

A conductance-based sensor to measure liquid film thickness during annular two-phase flows in microchannels has been developed in the present study. The liquid film plays an important role on the characterization of two-phase annular flows. The mean thickness and the presence of interfacial waves influence the heat transfer rate, critical heat flux and pressure drop. The proposed sensor has a ring-shaped design and targets the measurement of films thinner than 50 µm in order to provide detailed information on the liquid film behavior during wall dryout events. It is fabricated on a TEMPAX wafer with micro-electro-mechanical systems (MEMS) technologies. The performance of the prototype device is assessed by using aqueous solutions of known conductivity and imposing liquid films with prescribed thicknesses above the sensor. The effects of the geometrical parameters on the sensor behavior are discussed with the aid of numerical simulation and experimental results. It is found that increasing the size of the electrodes increases the measured electrical signals, while increasing the spacing between the electrodes decreases the measured signal.