Thermo-fluid dynamic Time-of-Flight flow sensor system

The authors report on a novel linear time-invariant (LTI) modeling of a flow sensor system based on thermal Time-of-Flight (TOF) principle by using pulsed hot wire anemometry. Thermal heat pulses are electrically generated at the hot wire centered in a pipe, carried along by the fluid in flow direction, and detected at several positions downstream. The flow sensor consisting of a hot wire and several temperature sensors is entirely regarded as an LTI system which is characterized by the fluid velocity, the fluid media and some heat transfer effects. Hence, a mathematical model with thermodynamic and fluid mechanical parameters is built. The thermo-fluid dynamic step and impulse responses of the hot wire are analyzed with respect to their signal parameters like rise and fall time and referred to the parameters of thermodynamics and fluid mechanics. The flow velocity and flow media are determined by signal analysis of the hot wire and by the thermo-fluid dynamic TOF measurement.