hotwireanemometers

A hot-wire anemometer is an instrument used to measure fluid flow velocity. It operates on the principle of convective heat transfer. A thin wire, typically made of platinum or tungsten, is heated to a temperature above the ambient fluid temperature. As the fluid flows past the wire, it carries heat away through convection. The rate of heat loss is dependent on the velocity of the fluid.

By measuring the electrical power required to maintain the wire at a constant temperature or by measuring the temperature of the wire when a constant current is applied, the fluid velocity can be determined. There are two primary modes of operation: constant temperature (CT) and constant current (CC). In constant temperature mode, a feedback circuit adjusts the current to keep the wire's resistance, and thus its temperature, constant. In constant current mode, a fixed current is applied, and the resulting change in wire resistance (due to cooling) is measured, which directly relates to temperature and velocity.

Hot-wire anemometers are known for their high frequency response, making them suitable for measuring turbulent flows and rapid fluctuations in velocity. They are sensitive to fluid temperature and pressure, and their calibration can drift over time, requiring periodic recalibration. They are commonly used in atmospheric research, wind tunnel testing, and automotive engine diagnostics. However, they are delicate and can be easily damaged by particulate matter in the fluid.