Potential Probe (Conductance Anemometer)
The principle of the conductance anemometry is based on the deducibility of the velocity from the measurements of an electrical field induced by the motion of an electrically conducting fluid in the presence of an external magnetic field .
The function of the potential-difference probe is governed by the Ohm´s law in moving fluids.
In general, the measured electric field cannot be considered as . However, in special cases such as for MHD channel flows at high Hartmann numbers and a small wall conductance ratio cw (1/Ha << cw << 1) the total current density can be neglected compared to the induced one:
Let us assume the magnetic field as uniform and directed transverse to the velocity component which should be measured. Consequenty, the measured electric potential drop between the electrodes, separated by the distance l, has the following simple dependance on the fluid velocity
Due to the following factors this measuring technique appears as very attractive:
Measuring principle of the potential-difference probe
- the simple relationship between the flow velocity and the measured signal
- the possibility to make the sensor extremely small
- the instantaneous response
- an external magnetic field is already present in MHD applications