Electromotive force induced by the moving non-magnetic phase in ferrofluids.

• A concept of kinetic-to-electrical energy conversion is presented. • The idea can be used as a non-contact sensor to monitor the flow state. • Formula to explain the variation of the electromotive force is derived. • The corresponding voltage waveforms of flow patterns are obtained. This paper presents a mechanical-to-electrical energy conversion concept by using the upward movement of air bubbles in ferrofluids. As ferrofluids are magnetized by a magnetic field, the air bubbles passing through the induction coils will change magnetic flux in the coils and produce electromotive force. Therefore, the kinetic energy of air bubbles converts into electricity. The idea possesses a promising prospect to be applied in the non-contact sensor field, which can monitor the flow states of boiling two-phase flow in a heat exchanger and warn the deterioration of heat transfer. A millivolt-level induced voltage with a waveform like a sine wave can be generated. The induced voltage's peak value is approximately proportional to the air bubble's volume and velocity and tends to saturate as the magnetic field strength increases. [ABSTRACT FROM AUTHOR]