Dr. G. F. Jones
CURRENT RESEARCH
1. A Carbon Fiber, Air-Cooled Heat Exchanger For High Performance Electronics Cooling
Miniaturization, and the continued improvements in the
speed and performance of electronics and other heat-dissipating systems, places
an increasing demand on thermal management systems through the increase in power
densities. There is a challenge to provide new thermal management technologies
that will be able to handle the very large heat fluxes that arise from these
improved electronics. Among the candidates for technologies that possess a large
heat transfer rate per unit of heat-dissipating surface area is the Brush Heat
Exchanger (BHX). The BHX consists of a very large number of air-cooled,
small-cross-section, staggered fins of carbon-pitch fiber / epoxy matrix
construction packed in a rectangular enclosure.
Five BHX units were designed, built, and tested in this effort. The peak heat
flux for the unit having the best thermal performance approaches 19 W/sq. cm for
an air flow rate of 45 cfm. The associated thermal resistance for this BHX unit
ranges from less than 0.10 K/W to about 0.08 K/W; more than a factor of five
better than the average commercial air-cooled heat exchanger, a factor of two
better than the best available commercial unit, and a factor of nearly four
times better than that of the commercial, aluminum, finned heat sink tested in
this work. The peak pressure drop is about 1.6 psi. Very little acoustic noise
was perceived and no carbon particles from the fiber reinforced composite
portions of the BHX were detected in a downstream air filter, even after twelve
hours of testing for five different exchanger designs. Results are extremely
promising; nevertheless, several key areas have been identified for further
improvements including improved manufacturability and design changes.
2. 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 the peak temperature in contact with the electronic heat source, and the constraints are those associated with geometry, the theory of heat conduction and convection, and eventually pressure drop. That is, we will seek a family of solutions that minimize the objective function and determine the final solutions by applying the above constraints. Where possible, fabrication and testing of one or more of these more compact heat exchangers will be carried out with materials like carbon (which has an extremely large thermal conductivity), and carbon-epoxy matrix composites.
3. Thermal 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 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 - 60 C; an acceptable range that
precludes the need for any internal liquid cooling or external humidification of
feed gases.
Copyright 1999-2002 Villanova University Department of Mechanical Engineering
Last Updated 08/22/02 GFJ