(541g) Effects of Surface Modified Ferrofluids on Energy Induction in Oscillating Heat Pipes

Authors: 
Kumari, S., Mississippi State University
Monroe, J. G., Mississippi State University
Wijayapala, R., Mississippi State University
Vasquez, E. S., University of Dayton
Berg, M. J., Mississippi State University
Thompson, S. M., Mississippi State University
Walters, K. B., Mississippi State University
Co-precipitation and surface functionalization of ferrofluids containing nanoscale ferrous oxide and cobalt oxide was performed in order to gain stable ferrofluids without compromising magnetization capabilities. Both as synthesized and surface modified nanoparticles in an aqueous carrier solvent were used as the working fluids in oscillating heat pipes (OHP) for thermal energy transportation and electrical energy conversion. This novel scheme uses ferrofluidic induction to generate power via pulsating movement of ferrofluid, due to an axial thermal gradient and associated phase change, through an in-line solenoid between two magnets. To avoid nanoparticle aggregation in the ferrofluid during long usage periods and thermal cycling, a number of different ligands were examined as a surface modifiers to maintain the nanoparticles in solution, prevent agglomeration, and maximize the voltage signal from the solenoid. Characterization of the ferrofluid samples was performed using ATR-FTIR spectroscopy, dynamic light scattering (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic/magnetic force microscopy (AFM/MFM), and magnetometry. Cobalt ferrite nanoparticles surface-modified with a variety of different small molecule ligands (e.g., citric acid) demonstrated good magnetic strengths and also generated voltages close to those of the as synthesized (without surface modification) ferrofluids, while maintaining dispersion. A maximum effective thermal conductivity of 12.9 kW/m×K at 470 W power was measured for a non-harvesting ferrofluid test. The effectiveness of ferrofluids as OHP working fluids will be discussed along with the implementation of bias magnets in the harvesting configuration which enhanced OHP thermal conductivity by 11%.
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