Evaluation on thermocouples for the thermal time-of-flight flow measurement

The authors report on a flow measurement technique using the Thermal Time-of-Flight (TTOF) method. In this work the velocity of air flowing through a pipe was investigated. For this purpose a filament and several thermocouples were adopted. The filament served as a signal transmitter, which injected thermal pulses into the flowing fluid in the pipe. The generated thermal pulses propagated along the flowing direction towards the thermocouples. In three defined distances the injected thermal pulses were detected by three identical thermocouples, respectively. The time behaviour of the measured output signals was computed using the crosscorrelation process. The time delay of the output signals combined with the knowledge of the distances resulted in the flow velocity. In this work, a flow measurement technique in the velocity range of vmin = 0.01 m/s up to vmax = 1.20 m/s is presented considering laminar flow.