MAGNETIC NANOPARTICLE MORPHOLOGIES: DEVELOPING FERROFLUIDS FOR PULSATING FLOWS
This work involves the synthesis, characterization and utilization of different magnetic ferrofluids for hybrid thermal-to-electrical energy devices. By suspending magnetic nanoparticles in a fluid within a pulsating (or oscillating) heat pipe (PHP) with unique serpentine design, a pseudo-harmonic displacement of the internal vapor and condensate (pulsating flow) can be achieved when a temperature difference is imposed across the PHP length. During this operation, the PHP has an ultra-high thermal conductivity and no moving parts. In this study, we focus specifically on different colloidal suspensions of nano- and micron-sized iron oxide particles. In particular, the PHP performance with surface-coated nanoparticles suspended in acetone is discussed. The magnetic particles are surface-modified to prevent agglomeration; allowing the ferrofluid to behave as a liquid. Since temperature gradients drive the heat transfer and pulsating fluid flow, an evaluation of the thermal stability of the ferrofluids was performed. Dynamic light scattering measurements were used to assess the primary particle dimensions and aggregation; morphological characterization of these iron oxide magnetic particles was also performed using transmission electron microscopy. Also presented are preliminary studies using the multicore magnetic structures in a PHP with a solenoid (i.e. harvester) are discussed. This study demonstrates the capability of surface-coated, magnetic micro/nano-particles for use in energy harvesting and thermal management applications. The degradation of nanoparticle composites due to PHP thermal and phase-change operating cycles is discussed, giving experimental guidance for the design of nanoparticles and ferrofluids for future thermal management applications that utilize pulsating flows.