chapter  59
Thermal Anemometry
Pages 18

A thermal anemometer measures the velocity at a point in a žowing žuid-a gas or a liquid. Figure 59.1 shows a typical thermal anemometer used to monitor velocity in gas žows. It has two sensors-a velocity sensor and a temperature sensor-which automatically correct for changes in gas temperature. Both sensors are reference-grade platinum resistance temperature detectors (RTDs). œe electric resistance of RTDs increases as temperature increases. For this reason, they are one of the most commonly used sensors for accurate temperature measurements. œe electronics circuit passes current through the velocity sensor, thereby heating it toaconstant-temperature di¥erential (Tv − Ta) above the gas temperature Ta, and measures the heat qc carried away by the cooler gas as it žows past the sensor. Hence, it is called a “constant-temperature thermal anemometer.”