No description available.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

No description available.

The effect of die attach voiding on the thermal resistance of a hybrid integrated circuit package has been investigated. Voids with precisely controlled geometry, morphology, distribution, and different volume percentages are fabricated in the backside of the silicon chips by modern micro-photolithographic techniques. A large thin film resistor over the entire chip surface area served as a uniform heat generating source. A TO-3 steel package with beryllia substrate is used for chip packaging. Correlation of thermal resistance to power dissipation in the range studied is presented and discussed. The dependence of thermal resistance on void characteristics and total void area are demonstrated through infrared mapping of chip surface temperature; and the correlations are qualitatively analyzed. A brief discussion on die bond void reduction is also given.

University of Macau / Faculty of Science and Technology. / Department of Electromechanical Engineering

We report the results of a series of experimental studies in two interrelated areas: homogeneous nucleation and transient heat transfer in cryogenic liquids. We report the first determination of the homogeneous nucleation temperature of liquid helium I and liquid nitrogen employing a transient superheating technique. This technique in liquid helium involved the development of a new transient magnetoresistive thermometer which relies on the strong temperaure dependence of magnetoresistance in bismuth as a thermometric property. Our measurements of the homogeneous nucleation temperature for both liquid helium I and nitrogen are in good agreement with the predictions from the Becker-Doring Volmer-Zel'dovich-Frenkel nucleation theory. On the basis of such agreement between theory and experiment in both liquid helium and liquid nitrogen we have developed a corresponding state analysis applicable to the case of homogeneous nucleation in liquid noble gases, both quantum and classical. Predictions of the homogeneous nucleation temperature and surface tension of several hydrogen isotopes are made from such a quantum mechanical law of corresponding states. We also comment on the limiting superheat temperature of liquid helium I. It is suggested that a comparison between the limiting superheat temperaure and the peak nucleate boiling temperature is meaningless and that the reported agreement between the two is largely fortuitous. In the studies of transient heat transfer in helium we find that the heat transfer from a solid into liquid helium is markedly enhanced by the application of a visible pulse of light. In liquid nitrogen we find that a transition to stable film boiling can be observed for power values as low as 40 per cent of the steady-state peak heat flux.

No description available.

Natural convection provides a means for circulating fluids without the use of pumps. This type of system is of great interest for a wide variety of applications, including solar heaters, process industry, and nuclear reactors. Natural convection will play a vital role in the area of passive safety and reliability, particularly for the development of Generation IV nuclear energy systems. This study mainly focuses on the linear stability analysis of asymmetrically heated/cooled natural convection loops with large temperature variations across the heated core. The study targets the Argonne Lead Loop Facility (ALLF), a concept for an experiment loop to support the development of the Secure Transportable Autonomous Reactor-Liquid Metal (STAR-LM) at Argonne National Laboratory, using lead-bismuth eutectic (LBE) as the primary reactor coolant. A one-dimensional linear stability analysis is performed and the Nyquist criterion is employed to find the linear stability boundary of both forward and backward circulations. It was found that the natural circulations could be linearly unstable in a high Reynolds number region. Increasing loop friction makes a forward circulation more stable, but destabilizes the corresponding backward circulation under the same heating/cooling conditions. The preliminary results suggest that as the Peclet number decreases, the forward circulation is prone to become unstable while the backward circulation is prone to remain stable. / Graduation date: 2003