Session: 12-06-01: Boiling Heat Transfer and Flow Instabilities

Paper Number: 173161

Ultrasonic-Enhanced Nucleate Boiling for Next-Generation Dual-Mode Cold Plates and Flow Systems in Ai Chip Cooling 

This presentation and referenced publications [1] highlight the benefits of integrating ultrasonic piezoelectric transducer-induced micro-vibrations with micro-structured boiling surfaces in cold plates for Two-phase Direct-to-Chip (2-Φ D²C) liquid cooling of AI chips. Without piezoelectric transducers, enhanced nucleate boiling (ENB-1) achieves high heat transfer coefficients (HTC) of 60–100 kW/m²·°C and critical heat flux (CHF) of 250–350 W/cm² using R1233zd or similar fluids (e.g., HFE-7000 in experiments). Unlike competing solutions (e.g., Accelsius, ZutaCore), our comprehensive design methodology integrates a micro-structured cold plate, optimized flow loop, and operational protocols, enabling scalable ENB-1 and the superior ENB-2 configuration for enhanced cold plate and coolant distribution unit (CDU) performance.

Ultrasonic micro-vibrations enable ENB-2, inducing controlled flash boiling for 10,000–20,000 hours at low power (<1% TDP) with a high benefit-to-cost ratio. ENB-2 reduces chip temperatures by 15–20°C, requiring minimal material changes (e.g., copper/Monel) and validation on a chip manufacturer’s thermal test vehicle (TTV) with optimized Thermal Interface Material (TIM). This approach minimizes chip-to-fluid thermal resistance and enhances lateral heat spreading, mitigating hot spots without Direct-to-Silicon cooling.

On-off ultrasonic feather-like vibrations elevate microlayer temperatures of nucleating bubbles, transitioning ENB-1 ebullition cycles [2–5] to ENB-2 via acoustothermal heating [6] and acoustic streaming [7]. This triggers transient increases in non-equilibrium liquid-to-vapor mass flux [8] within bubble microlayers over millisecond-scale advance/recede cycles, driving a sustained vapor-phase pressure rise in the test section, as observed in experiments. Energy balance and Ansys-Fluent modeling confirm that this pressure rise and sustained microlayer temperature increase [1] leverage substrate and fluid thermal inertia to extract significant heat (in joules) from the chip via the cold plate, reducing its temperature by 15–20°C. These low-power vibrations (<1% TDP) shift ENB-1 saturation boiling to ENB-2’s sustained flash boiling in spinodal regions [6].

This approach also enables efficient waste heat recovery into clean electricity. High-pressure R1233zd vapor from data centers can be condensed into an Organic Rankine Cycle (ORC, using R1233zd) liquid stream via a Heat Recovery Vapor Generator integrated with a Combined Cycle Power Plant (CCPP) gas turbine exhaust.

Experimental and modeling results are detailed in the presentation and extensively discussed in [1].

References:

1. NSF-CBET-2327965-ProjectReport-2025 for new results. Additional findings are disseminated in 4–5 forthcoming journal papers.

2. Dhir, Vijay K. "Mechanistic prediction of nucleate boiling heat transfer–achievable or a hopeless task?." (2006): 1-12.

3. Kim, Jungho. "Review of nucleate pool boiling bubble heat transfer mechanisms." International Journal of Multiphase Flow 35, no. 12 (2009): 1067-1076.

4. Gerardi, Craig, et al. "Measurement of nucleation site density, bubble departure diameter and frequency in pool boiling of water using high-speed infrared and optical cameras." (2009).

5. Zhang, Lenan, et al. "A unified relationship between bubble departure frequency and diameter during saturated nucleate pool boiling." International Journal of Heat and Mass Transfer 165 (2021): 120640.

6. Pillai, Rohit, et al. "Acoustothermal atomization of water nanofilms." Physical Review Letters 121, no. 10 (2018): 104502.

7. Sadhal, S. S. "Acoustofluidics 13: Analysis of acoustic streaming by perturbation methods." Lab on a Chip 12, no. 13 (2012): 2292-2300. Also see COMSOL 6.1 [2022] for simulating Acoustic Streaming.

8. Lu, Zhengmao, et al. "A unified relationship for evaporation kinetics at low Mach numbers." Nature Communications 10, no. 1 (2019): 2368.

9. López, David Reguera. "Nucleation phenomena: The non-equilibrium kinetics of phase change." Contributions to Science 11, no. 2 (2016): 173-180.

Presenting Author: Amitabh Narain Michigan Technological University

Presenting Author Biography: Prof. Amitabh Narain (Ph. D., University of Minnesota, 1983) is a Professor in the Department of Mechanical Engineering at Michigan Technological University, USA; a Fellow of the ASME; current Associate Editor of ASME’s AOJE (2016-), and a past AE of the Journal of Heat Transfer (2015-2021). At the department level, he has served as the Director of the Energy-Thermo-Fluids Area, Executive Committee, and as the chair of its promotion-and-tenure/faculty development committee. His current research areas deal with state-of-the-art experimental and modeling techniques for (enhanced nucleate boiling or ENB) as well as single-phase flows. At the system level, these works relate to energy technologies such as direct on-chip liquid cooling (using ENB) of electronics and associated thermal management with emphasis on waste heat recovery for environment-friendly data centers. Dr. Narain’s research has received regular funding (from NSF, NASA, and industry) from 1986 – 2018, and from 2023 - 2026. He is a PI or Co-PI on external grants totaling approximately $ 3 million (with $2 million as PI). Dr. Narain has authored over 75 peer-reviewed articles. His research accomplishments have been highlighted through keynote and invited lectures. He is very active in teaching and mentoring students (graduate and undergraduate), as well as in national/international-level professional leadership and service. Dr. Narain has served on several government panels and ASME committees: HTD-K8 (past Chair and Vice-chair), HTD-K13 (Member), and AMD-Fluid Mechanics Committee (Past Chair and Vice-Chair). Over the past twenty years, he has also been an active lead organizer for several symposia, topics, and sessions for ASME and other international conferences.

Authors:

Amitabh Narain Michigan Technological University
Hardik Bhutka Michigan Technological University
Atharva Kanetkar Michigan Technological University
Nirgun Mohite Michigan Technological University