SUMMARY

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.