Title: Phase Change Materials For Vehicle And Electronic Transient Thermal Systems
Professor F. Patrick McCluskey, Chair
Professor Neil Goldsman (Dean’s Representative)
Professor Hugh Bruck
Professor Michael Ohadi
Professor Jungho Kim
Date & Time: November 5, 2020; 3:00-5:00pm
Abstract: Most vehicle operating environments are transient in
nature, yet traditional subsystem thermal management addresses peak
load conditions with steady-state designs. The large, overdesigned
systems that result are increasingly unable to meet target system
size, weight and power demands. Phase change thermal energy storage
is a promising technique for buffering thermal transients while
providing a functional thermal energy reservoir. Despite significant
research over the half century, few phase change material (PCM) based
solutions have transitioned out of the research laboratory. This work
explores the state of phase change materials research for vehicle and
electronics applications and develops design tool compatible modeling
approaches for applying these materials to electronics packaging.
This thesis begins with a comprehensive PCM review, including over 700
candidate materials across more than a dozen material classes, and
follows with a thorough analysis of transient vehicle thermal systems.
After identifying promising materials for each system with potential
for improvement in emissions reduction, energy efficiency, or thermal
protection, future material research recommendations are made
including improved data collection, alternative metrics, and increased
focus on metallic and solid-state PCMs for high-speed applications.
Following the material and application review, the transient
electronics heat transfer problem is specifically addressed.
Electronics packages are shown using finite element based thermal
circuits to exhibit both worsened response and extreme convective
insensitivity under pulsed conditions. Both characteristics are
quantified using analytical and numerical transfer function models,
including both clarification of apparently nonphysical thermal
capacitance and demonstration that the convective insensitivity can be
quantified using a package thermal Elmore delay metric.
Finally, in order to develop design level PCM models, an energy
conservative polynomial smoothing function is developed for Enthalpy
and Apparent Capacity Method phase change models. Two case studies
using this approach examine the incorporation of PCMs into electronics
packages: substrate integrated Thermal Buffer Heat Sinks using
standard finite element modeling, and direct on-die PCM integration
using a new phase change thermal circuit model. Both show
effectiveness in buffering thermal transients, but the metallic phase
change materials exhibit the best performance with significant
sub-millisecond temperature suppression, something improved cooling or package integration alone were unable to address.