The dynamic characteristics of hot film anemometers in liquid metals

Because of the large thermal conductivity of a liquid metal, its thermal boundary layer around a heated anemometer sensor is also very large. Consequently, the thermal capacity of the thermal boundary layer affects the response of the anemometer to fluctuating velocity. This thesis concerns the impairment of the anemometer signal by the thermal boundary layer and comprises both theoretical and experimental approaches. Theoretically, the response is analyzed by assuming that an infinite cylinder is exposed to a velocity with a small sinusoidal component. The velocity field is approximated by Oseen flow as well as potential flow. It is found that the responses of an anemometer system in these two flow fields are effectively identical when the Peclet number is below 0.4. Both the amplitude and the phase lag of the anemometer signal are found to be significantly affected for velocities and frequencies of interest in measurement of turbulence in liquid metals.