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    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.