This work presents development of a novel thermal sensor to measure the fluid phase and composition in a microchannel. As the sensor employs an AC hot-film technique to monitor the fluid state, it is more sensitive and noise-resistant than the conventionally used DC technique. The sensor is composed of a thin-film heater integrated into a PDMS microchannel fabricated on a glass substrate. Monitoring the liquid-gas phase interface in a microchannel is demonstrated by examining water injection and liquid evaporation processes. The results show good agreement with those by optical inspection. Also, real-time monitoring the composition of ethanol/water mixtures flowing in a microchannel is demonstrated. The presented sensor is expected to be used in various potential applications, including multiphase flow sensors, lab-on-a-chip devices, micro heat exchangers and micro fuel cells.

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