Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Supervisor(s)

Dr. Kamran Siddiqui

Abstract

Phase change materials (PCMs) used in thermal energy storage (TES) system as heat storage media can play crucial role in various engineering applications. PCMs have the inherent ability to store large amount of heat by exploiting their heat of fusions, predominantly during their solid-liquid phase-change period. The present study reports an experimental investigation on the melting process in a PCM and the associated heat transfer in a transient manner. The experiments were conducted in a rectangular chamber filled with paraffin wax used as the PCM and, a cylindrical copper tube with different geometries and orientations as the heat source.

The simultaneously recorded temperatures and the images enabled to analyze the spatio-temporal behavior of the PCM during melting and provided a platform to characterize various important thermophysical parameters associated with the phase transition process. The results show a nonlinear melting rate of the PCM and a wavy and non-uniform profile of the solid-liquid interface. The results also show the development of convective motions within the liquid PCM which influenced the local heat transfer coefficient in a transient manner and is believed to have immensely influenced the nature of this distinctive and non-linear pattern of the solid-liquid interface. The convective heat transfer coefficient, h increased sharply at the early stage of melting, followed by a more gradual increment in h, which then became nearly steady when the melted fraction reached approximately two-third of the total PCM volume. The continuous change in the structures of the flow inside the convective cell is believed to have significantly influenced the heat transfer coefficient. The results enabled to characterize various important thermophysical correlations in non dimensionless form associated with the PCM during the melting process to comprehend the convective heat transfer behavior and to extend the understanding on the interface dynamics. These correlations were found to have similar trends compared to other empirical correlations found in the literature.

On the other hand, most PCM suffer from the inherently common problem of low thermal conductivity which hampers in the heat transfer rates. This study also focused on the understanding of thermal conductive enhancement in PCM using nanoparticles with it. Results show a substantial improvements in various thermophysical parameters of the PCM with a small percentage of nanoparticles added.


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