SUBJECT: Ph.D. Proposal Presentation
BY: Ammar Osman
TIME: Wednesday, April 3, 2024, 9:00 a.m.
PLACE: Virtual,
COMMITTEE: Dr. Yogendra Joshi, Chair (Mechanical Engineering)
Dr. Andrei G. Fedorov (Mechanical Engineering)
Dr. Mostafa Ghiaasiaan (Mechanical Engineering)
Dr. Muhannad Bakir (Electrical Engineering)
Dr. Sreekant V.J. Narumanchi (National Renewable Energy Laboratory)


Coldplates are a critical component in various cooling applications, such as cooling of data centers and thermal management of power electronics. The unprecedented increase in power densities has led to a growing interest in two-phase coldplates as a promising solution due to their high heat transfer coefficients and improved temperature uniformity. Recent flow boiling studies have focused on fin-enhanced silicon microgaps and microchannels, given their importance in cooling high-power-density chips operating at ultra-high heat fluxes. However, most of the research on flow boiling in mini- and macro-scale configurations has been limited to channels and tubes, overlooking crucial geometries such as pin-fin-enhanced mini-channels. This literature gap, particularly the study of flow boiling in pin-fin-enhanced channels at the meso/mm-scale, has resulted in a lack of data, flow regime maps, and correlations crucial for the design of two-phase coldplates. The present work addresses this gap by conducting an extensive flow boiling study in meso-scale pin-fin coldplates using HFE-7200 dielectric fluid. The study aims to develop flow regime maps, pressure drop, and heat transfer correlations for flow boiling in pin-fin-enhanced mm-scale channels for a range of flow rates, inlet subcooling, and geometric parameters. Additionally, the study evaluates the capability of two-phase coldplates to manage non-uniform heating conditions with hotspot heat fluxes up to 1000 W/cm2, providing a realistic representation of heat dissipation for applications such as power electronics. High-speed visualizations were utilized to provide insights into the flow regimes and bubble dynamics. A modeling framework is developed to assist in the design of two-phase pin-fin coldplates by improving the state-of-the-art Lee model. An improved Lee model is proposed, considering both the change in saturation temperature with pressure and the required surface superheat for the onset of nucleate boiling.