Engineering analysis for the design of thermal transient anemometers

An operating theory for the thermal transient anemometer (TTA) is derived, and a concise methodology for designing practical TTA sensors and system parameters for operation in air flows is developed on the basis of this theory. A TTA is a novel measuring device with a thermocouple sensor that measures changes in temperature over time to provide a measure of fluid flow velocity. The thermocouple flow sensor is periodically heated by an electrical pulse, and the rate of cooling between pulses is related to the local mean flow velocity. Perhaps the most important advantage of the TTA is that a standard sheath thermocouple can be used as a flow sensor, which results in a more rugged and inexpensive probe than a classical thermal anemometer. A fundamental operating theory is developed for the TTA under generalized flow conditions. A more specific theory for the TTA sensor operating in air flows is then derived from the general theory. Sensor design and operating parameters are investigated. The performance characteristics of the TTA sensor operating under air flows at elevated fluid temperature and at time-varying flow velocity and time-varying fluid temperature conditions are studied. Flow bench tests and computer simulations are used to validate the operating theory derivations. On the basis of the validated theory, a concise methodology for the design of practical TTA sensors and systems is developed. A TTA system and construction of a practical TTA sensor design based on this methodology are described. The results of tests performed on the sensor are presented.