US Patent 7856892 Flow-rate measuring method and flow-rate measuring device

A measurable flow-rate range is increased to enhance usability. A flow-rate measuring method for measuring the flow rate of a fluid inside a tube is provided. This method uses a thermal-marker generator that heats the fluid flowing through the tube from the outside thereof to generate a thermal marker in the fluid inside the tube and a thermal-marker detector disposed downstream of the thermal-marker generator and configured to detect the thermal marker in the fluid inside the tube generated by the thermal-marker generator, so as to measure the flow rate on the basis of the distance between the thermal-marker generator and the thermal-marker detector, a time period between a point at which the thermal marker in the fluid inside the tube is generated by the thermal-marker generator and a point at which the thermal marker is detected by the thermal-marker detector, and the cross-sectional area of the tube. In this method, the thermal-marker generator heats the fluid by a microwave heating technique, and microwaves are applied to the fluid by using a microstrip line.