Date of Graduation

12-2020

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering (MSME)

Degree Level

Graduate

Department

Mechanical Engineering

Advisor

David Huitink

Committee Member

Lauren Greenlee

Second Committee Member

Rick J. Couvillion

Keywords

Brownian relaxation, induction heating, iron oxide, nanoparticles, phase change materials, viscosity

Abstract

This study investigates the induction heating response of uncapped iron oxide nanoparticles sonically dispersed as a nanofluid and mechanically distributed in solid phase change materials. The nanoparticles examined have a mean diameter of 14.42 nm and are magnetically heated in an alternating magnetic field at an amplitude of 72.6 kA/m at frequencies of 217, 303, and 397 kHz. Nanoparticle characterization was undertaken through transition electron microscopy, x-ray diffraction, and dynamic light scattering when in suspension. Carrier fluids were characterized through viscosity, heat capacity, and density measurements which were used in the calorimetric calculation of the specific absorption rate (SAR) of the samples which is based on the nanoparticle concentration, carrier medium heat capacity, and the time-temperature response. The SAR of these samples is compared based on nanoparticle concentration, field frequency, and carrier medium viscosity. All samples types demonstrate SAR reductions with increasing nanoparticle concentration and SAR enhancement with increasing frequency. Nanofluid samples demonstrate a peak SAR value at the lowest viscosity examined, 1.024 mPa.s, with SAR attenuation with increasing viscosity up to 17.12 mPa.s. However, samples ranging from 171.6 to 234 mPa.s saw little variation with viscosity denoting the inhibition of Brownian relaxation in these samples. Dynamic light scattering of the nanofluids illustrates nanoparticle clustering which corresponds to viscosity potentially muddying the effective contributions of Brownian relaxation. Nanoparticles embedded in a solid PCMs of Paraffin wax and D-Sorbitol were investigated to reasonably characterize the SAR output of Néel relaxation dominated heating. The SAR results of the two PCM mediums correspond well at each concentration and field frequency demonstrating the Néel contribution to heating and the reasonable assumption of inhibited Brownian relaxation. Comparisons of SAR between solid embedded PCM samples and highly viscous nanofluids confirms Brownian inhibition at high viscosity for these nanoparticles. Analysis of the onset of Brownian relaxation during heating with a solid to liquid phase change sees an approximately 15.6 % increase in the SAR of the low viscosity liquid Paraffin with a 10 % decrease in SAR noted for the extremely viscous liquid D-Sorbitol. This result is attributed to the disparate liquid environments where nanoparticle settling is pronounced at low viscosity in Paraffin. Discussion on the precise contribution to SAR of Brownian relaxation is presented based on a limited set of data with consideration given to variations in SAR of the PCM samples for solid versus liquid states of heating. This study encompasses a wide range of carrier mediums and provides a thorough analysis of the heating response of iron oxide nanoparticles with focus on the Brownian contribution to heating.

Available for download on Saturday, December 17, 2022

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