Publikationen

Lorentz force velocimetry (LFV) is a noncontact electromagnetic flow measurement technique that is currently successfully applied for velocity measurements in liquid metals both in laboratory experiments and industry. However, up to now the application of LFV was restricted to conducting fluids with electrical conductivities of the order of 106 S/m such as are encountered in liquid metals. Here we demonstrate that LFV can be successfully extended to poorly conducting fluids (electrolytes) by using high-resolution force measurements.

We report an investigation of the motion of a freefalling permanent magnet in an electrically conducting pipe containing an idealized defect. This problem represents a highly simplified yet enlightening version of a method called Lorentz force eddy current testing which is a modification of the traditional eddy current testing technique. Our investigation is a combination of analytical theory, numerical simulation and experimental validation. The analytical theory allows a rigorous prediction about the relation between the size of the defect and the change in falling time which represents the central result of the present work. The numerical simulation allows to overcome limitations inherent in the analytical theory. We test our predictions by performing a series of experiments. We conclude that our theory properly captures the essence of Lorentz force eddy current testing although a refinement of the experiment is necessary to reduce the discrepancy to the predictions. In spite of its apparent simplicity the present system can serve as a prototype and benchmark for future research on Lorentz force eddy current testing.