Inline Microfluidic Thermal Conductivity Sensor Using A Suspended Silicon Heater

This paper reports a sensor for the inline measurement of the thermal conductivity of liquids at flow rates up to 1 g/h. A highly-doped silicon heater is suspended in the microchannel. The sensor is characterised for thermal conductivity values ranging from 0.169 W/mK (isopropanol) up to 0.617 W/mK (water), showing an accuracy within 3% of full scale. The suspended heater is designed to transport heat directly into the fluid, minimising heat losses to the environment. Moreover, cavities on either side of the microchannel increase the thermal isolation which further reduces the power consumption. The thermal conductivity of the fluid is determined by measuring the temperature increase when the heater dissipates 10 mW of power. Furthermore, the fabrication technology allows further on-chip integration with other inline microfluidic sensors.