Varmttrådanemometre

Varmttrådanemometre, often translated as hot-wire anemometers, are instruments used to measure fluid flow velocity. They operate based on the principle of convective heat transfer. A thin electrically heated wire, known as the sensing element, is placed in the fluid stream. As the fluid flows past the wire, it carries heat away from it. The amount of heat carried away is directly related to the velocity of the fluid.

There are two main modes of operation for hot-wire anemometers: constant temperature (CTA) and constant current (CCA). In CTA mode, a feedback circuit maintains the temperature of the sensing wire at a constant level. As the fluid velocity increases, more heat is lost, and the circuit must supply more current to keep the wire at the set temperature. The required current is then a measure of the velocity. In CCA mode, the current flowing through the wire is kept constant, and the resulting change in the wire's resistance, due to cooling, is measured. This change in resistance directly correlates to the fluid velocity.

Hot-wire anemometers are known for their high sensitivity and good frequency response, making them suitable for measuring turbulent flows and rapid fluctuations in velocity. They are commonly used in various fields, including aerodynamics, meteorology, HVAC (heating, ventilation, and air conditioning) system balancing, and in internal combustion engine research. However, they can be fragile, require careful calibration, and can be affected by changes in fluid temperature and pressure.