On the energy harvesting and heat transfer ability of a ferro-nanofluid oscillating heat pipe

A unique thermal-to-mechanical-to-electrical energy conversion process is demonstrated via thermally excited, pulsating ferro-nanofluid within a solenoid-equipped oscillating heat pipe (i.e., ferrofluid-OHP or FF-OHP). The FF-OHP was charged with an aqueous cobalt ferrite ferro-nanofluid, comprised of custom synthesized CoFe2O4 nanoparticles surface-modified with citric acid for increased suspensibility. Annular bias magnets were placed directly above and below the FF-OHP solenoid to temporarily magnetize the internal, oscillating ferrofluid. During FF-OHP operation, a measured peak-to-peak voltage of similar to 2 mV was measured across the solenoid due to electromagnetic induction. When filled with ferro-nanofluid, the OHP heat transfer was enhanced (relative to pure water) by similar to 58% with bias magnets and similar to 71% without bias magnets. A maximum effective thermal conductivity of similar to 12.9 kW/m.K was achieved in the FF-OHP at similar to 470 W of heat input. With the bias magnets installed (i.e., harvesting configuration), the FF-OHP effective thermal conductivity was similar to 11% lower than when the bias magnets were not present, and this is attributed to an increase in ferrofluid viscosity due to particle magnetization in the bias field. The FF-OHP/solenoid harvesting process is a novel means for accomplishing thermal-to-electrical energy conversion while maintaining high heat transfer capabilities and extreme temperature functionality. (C) 2018 Elsevier Ltd. All rights reserved.