Session: 12-13-02: Heat Transfer in Electronic Equipment II

Paper Number: 173528

Role of Surface Textures in Bubble Dynamics During Pool Boiling at Subatmospheric Pressures 

The growing demand for energy-efficient and thermally robust data center cooling systems has accelerated the development of advanced heat dissipation technologies. As data centers continue to scale in capacity and computational density, traditional air-based cooling methods are increasingly insufficient to manage the escalating heat loads. Liquid cooling strategies have emerged as attractive alternatives, offering higher thermal conductance and the potential for localized, high-flux heat removal. Among the available coolants, water remains a particularly promising candidate due to its high thermal conductivity, large specific heat capacity, low cost, non-toxicity, and environmental friendliness. However, its relatively high boiling point (~100 °C at atmospheric pressure) poses a challenge for cooling modern IT hardware, which operates optimally at lower temperatures. To overcome this challenge, subatmospheric pressure boiling has emerged as a potential solution to enable water to boil at temperatures closer to the desired operational range. Nevertheless, the thermal performance of boiling, specifically, the heat transfer coefficient (HTC) and critical heat flux (CHF), is affected by the pressure. Simultaneously, surface texturing has been widely employed to enhance nucleate boiling performance, with demonstrated improvements in both HTC and CHF. The interplay between pressure regulation and engineered surface textures remains poorly understood, particularly in the context of low-pressure environments. To address this knowledge gap, this study investigates the role of surface textures in modulating bubble dynamics during pool boiling at subatmospheric pressures. High-speed imaging is employed to capture transient bubble behavior on textured surfaces under varying pressure conditions. The recorded videos are analyzed using BubbleID, our in-house developed artificial intelligence model capable of extracting both static features (e.g., bubble size distribution, number of bubbles, vapor fraction, etc.) and dynamic features (e.g., bubble growth rate, departure frequency). By correlating bubble dynamics with measured thermal performance, the combined effects of pressure and surface textures on boiling heat transfer are investigated. Our results show that pressure significantly alters bubble dynamics, with lower pressures producing larger and slower-growing bubbles. Moreover, while both HTC and CHF are affected by pressure and surface textures, our results show that pressure plays a more critical role in HTC, and the effect of surface textures is more pronounced on CHF. This suggests the possibility of decoupled control over HTC and CHF depending on operational priorities. Our results also show that at low pressures (7 – 20 kPa), boiling hysteresis at CHF is significantly mitigated, making CHF a less severe point of failure compared to atmospheric pressure tests.

Presenting Author: Mohammad Ishraq Hossain University of Arkansas

Presenting Author Biography: Mohammad Ishraq Hossain is a graduate student pursuing his MS in Mechanical Engineering from Fall 2024. He is from Bangladesh and graduated from the Islamic University of Technology in 2023. His current research centers on liquid-vapor phase-change processes for electronics cooling, specifically, pool boiling at subatmospheric pressures and acoustic sensing of flow boiling.

Authors:

Mohammad Ishraq Hossain University of Arkansas
Christy Dunlap University of Arkansas
Han Hu University of Arkansas