Energy harvesting via thermo-piezoelectric transduction within a heated capillary

Abstract

Thermal-to-kinetic-to-electrical energy conversion is demonstrated through the use of a piezoelectric transducer (PZT) integrated within a section of an oscillating heat pipe (OHP) partially filled with water. The sealed PZT transducer was configured as a bow spring parallel to the dominant flow direction within the OHP. The bottom portion of the OHP was heated in increments of 50 W, while its top portion was actively cooled via water blocks. At ∼50 W, the internal fluid started to oscillate at ∼2–4 Hz due to the non-uniform vapor pressure generated in the OHP evaporator. Low-frequency fluid “pulses” were observed to occur across the flexed, in-line piezoelectric transducer, resulting in its deflection and measureable voltage spikes ranging between 24 and 63 mV. The OHP, while having its internal fluid enthalpy harvested, was found to still have an ultra-high thermal conductivity on-the-order of 10 kW/m K; however, its maximum operating heat load decreased due to the pressure drop introduced by the PZT material. The thermo-piezoelectric harvesting concept made possible via the thermally driven fluid oscillations within an OHP provides a passive method for combined energy harvesting and thermal management that is both scalable and portable.