Heat Transfer in a Glass-Forming Process
In order to evaluate the spatial and
temporal removal of heat from the parison
during blank mold contact, forming
simulations are completed using the forming
code, Polyflow. These simulations include
large surface deformations, viscoelastic
behavior, conjugate heat transfer, and the
non-trivial contact phenomena at the
glass-mold interface. Due to the complexity
and size of these models, they are
computationally expensive and very time
consuming. In addition to this, there is
some ambiguity in the applied heat transfer
coefficient (or thermal contact resistance)
required to complete the simulations. It is
desirable to analytically and experimentally
quantify this heat transfer coefficient. A
one-dimensional finite-difference model of
transient glass to mold heat transfer has
been developed and validated for this
purpose. This model was modified to
calculate heat flux from mold surface
temperature measurements taken in both a
controlled experimental setting, as well as
on the Emhart Glass Research Center (EGRC)
production machine. This heat flux was in
turn, used to predict the temperature
distribution in the glass and a
corresponding heat transfer coefficient. The
purpose of the experimental data collection
was to isolate the effects of operating
conditions in a controlled environment. This
study reports the effects of initial mold
temperature, initial glass temperature, and
pressing pressure on the resulting heat
fluxes and heat transfer coefficients. The
data collected in these experiments, in
conjunction with the numerical reduction
codes have shed light on the importance of
different parameters governing heat transfer
during the forming process, and is the focus
of this thesis. With this knowledge, a
simplified first order predictive model for
heat flux and heat transfer coefficients was
developed. Upon completion of this thesis,
the simplified model will be used in order
to develop a more sophisticated mechanistic
model, which will attempt to capture the
physics of the process, as well as eliminate
the need to perform a full forming- model in
Polyflow. Cooling of High-Power Electronic
Equipment with a Compact Heat Exchanger
Developed from Constructal Theory
We
consider the general problem of convective
cooling of high-power electronic equipment.
We seek the answer to the question: “what is
the theoretical maximum thermal performance
for an air-cooled compact heat exchanger?”
Once obtained, a follow-on question of equal
importance addresses the optimization of
this heat exchanger considering
simultaneously thermal performance and
pressure drop. We propose to approach the
solution to this problem by using the Constructal theory of Bejan. Constructal
theory attempts to explain the origin of
structure in the macroscopic world by
optimizing the solutions from the
conservation laws governing the processes.
With it, a set of design formulas are
developed for an application by considering
first lower, and then higher, orders of
construction. The formulas may then be
applied to design a device with improved
performance. The objective function of the
Constructal optimization for this problem is
either the rate of heat transfer from the
heat source (for maximization) or the rate
of entropy generation in the heat exchanger
(for minimization), and the constraints are
those associated with geometry, the theory
of heat conduction and convection, and
pressure drop. Where possible, fabrication
and testing of one or more of these more
compact heat exchangers is carried out with
materials like carbon (which has a very
large thermal conductivity), and
carbon-epoxy matrix composites. This theory
is currently being applied to porous-media
heat exchangers for high-performance
electronics-cooling applications.
A Lightweight, Carbon Fiber Heat
Exchanger for High Performance Applications
In aircraft and aerospace applications
reducing weight is important to improve the
overall performance of the craft.
Carbon-fiber composite materials are known
to be lightweight and have high in-plane
thermal conductivities. These are used in
the manufacture of air-to-liquid and
radiant-panel heat exchangers which are the
focal points for an ongoing study. Key among
the analysis and design of these units is
the need to take advantage of the high
in-plane thermal properties and the
minimization of surface contact resistance
between mechanically bonded heat exchanger
constituents.
Management Strategies for Improved
Thermal Performance of Fuel Cells Miniature
thermoelectric coolers are employed along
the periphery of a bipolar plate in a proton
exchange membrane fuel cell to cool the
adjacent membrane exchange assemblies where
most of the waste heat is generated. We have
produced and run numerical models for the
thermal performance of fuel cells that use
this strategy. We find that this strategy
maintains the cell stack operating
temperature between 45 and 60 C; an
acceptable range that precludes the need for
any internal liquid cooling or external
humidification of feed gases.
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