Effect of harvesting module design on the thermal performance and voltage generation of a thermoelectric oscillating heat pipe

Abstract

A thermoelectric oscillating heat pipe (OHP) converts a temperature potential into electricity by exploiting its internal, cyclic fluid enthalpy. In this study, the energy harvesting ability of a tubular oscillating-magnet OHP (OMHP), a type of thermoelectric OHP that utilizes a floating, cylindrical magnet and externally-wrapped solenoid, was experimentally investigated over a range of heat inputs for evaluating how harvesting module design, e.g. size of induction magnet, number of solenoids, length of module, impacts its thermal and electrical performance. Two methods for constraining/positioning the floating cylindrical magnet, i.e. with internal posts or externally-located annular magnets (for repulsive forces), were considered. While using water as a working fluid at a 75% fill ratio, results demonstrate that the OMHPs operated as a traditional OHP, with effective thermal conductivities on-the-order of 5000 W/m K, while also generating electrical voltages up to ∼250 mV (peak-to-peak). The investigated OMHPs could accommodate up to 400 W of heat transfer while maintaining an average evaporator temperature below ∼100 °C; this heat transfer limit was found to decrease substantially when using internal posts over external annular magnets for magnet positioning. However, harvester modules with internal posts were found to produce significantly more electrical voltage due to the induction magnet’s increased freedom of motion in the absence of an external magnetic field. The heat transfer and electrical voltage generation needs for a given application must be balanced and this work will aid in designing the appropriate OMHP.