Novel humidity sensor using heat pipe: Phase transition thermally balanced sensor designed for measurement of high humidity at high temperature

•We developed a novel humidity sensor using the condensation heat of dew formed on a heat pipe.•The performance of the sensor was evaluated using a primary humidity standard.•This sensor is superior to psychrometers, particularly under harsh conditions.

We developed a novel humidity sensor using a heat pipe on the basis of a new measurement principle. The sensor measures humidity using the condensation heat of water on the surface of the heat pipe. Theoretical equations describing the measurement principle using a simple model were derived. Comparison experiments were performed for dew points in the range of 50 °C to 80 °C using a humidity standard generator based on the International System of Units (SI). The standard value and the value calculated using the theoretical equations were in reasonable agreement with each other (with a difference within 0.5 °C). The difference was further decreased to within 0.2 °C by employing a calibration curve using multiple regression analysis. The sensor was also experimentally compared to a psychrometer, confirming that the two devices have similar performance. The sensor does not require the replacement of wicks or a water supply, and the measurement region is made of metal, making the sensor superior to the psychrometer in terms of low maintenance, and long lifetime and high durability at high temperatures and high humidities.