Abstract The rapid growth of digitization and data-driven technologies is driving large-scale deployment of data centers worldwide. As societies become increasingly inference-hungry, the energy consumption of data centers continues to rise at an unprecedented rate, with a significant fraction of this energy being expended on thermal management and cooling infrastructure. Improving cooling efficiency has therefore become a critical challenge for the thermal management community, directly impacting both the sustainability and scalability of future computing systems. In this paper, we demonstrate an energy-efficient cooling solution based on chip-integrated two-phase cooling, which leverages liquid-to-vapor phase-change heat transfer to achieve high heat-flux dissipation at reduced pumping power and thermal resistance. This paper investigates an aggressive cooling architecture utilizing direct-on-die two-phase jet impingement on an NVIDIA Tesla V100 GPU without any thermal enhancement structures. By eliminating thermal interface material (TIM) and impinging the working fluid R1233zd(E), a low-global warming potential (GWP) (<1) refrigerant, directly onto the silicon backside, the primary thermal bottleneck is removed. Experimental results demonstrate a junction-to-coolant thermal resistance of 0.056 °C/W and a theoretical pumping power of only 0.172 W versus the conventional air-cooled cold plate of 0.1709 °C/W and a fan power of 39.9 W. Furthermore, the reliability of the direct-on-die cooling technique was validated through 200 h of continuous, stable operation. This study positions direct jet impingement as a highly efficient, compact, and sustainable solution for next-generation high-performance computing environments.
more »
« less
Immersion Cooling in Data Centers: A Comprehensive Review of Benefits, Challenges, and Future Directions
Immersion cooling has emerged as a promising solution for the escalating thermal management challenges in the contemporary and modern (next generation) data centers, where traditional air-cooling systems are increasingly inadequate due to rising power densities in microprocessors. The evolution of immersion cooling technologies, highlighting their benefits and the challenges associated with their implementation, is explored in this review. Two-phase microchannel cooling has often been cited as a highly efficient alternative, which can help achieve significant energy savings over air cooling. Subsequent studies have expanded on methods like refrigerant touch cooling, thermosiphon systems, and geothermal immersion cooling. All these strategies can help achieve enhanced energy efficiency, reduced operational costs, and improved Power Usage Effectiveness (PUE). Immersion cooling has been demonstrated to support denser CPU packaging and meet the demands of high-performance computing environments. Despite these advantages, challenges persist, including the need for specialized infrastructure, potential risks related to liquid handling, and integration with existing systems. Advances in environmentally friendly cooling fluids and optimized airflow management have begun to mitigate some of these issues. To fully realize the potential of immersion cooling, future research endeavors should focus on developing standardized protocols and best practices to facilitate its widespread adoption. Enhancing the compatibility of cooling fluids with a broader range of hardware components will be crucial, as will designing systems that are easier to integrate with existing data center infrastructure. Exploring hybrid cooling solutions that combine immersion cooling with other efficient methods could offer additional benefits. Further investigation into the long-term reliability, maintenance requirements, and environmental impacts of immersion-cooled systems is essential. Integrating immersion cooling with renewable energy sources and waste heat recovery systems could also enhance sustainability and operational efficiency (e.g., for thermal desalination and wood drying applications). The literature reports can be utilized to identify a clear trend toward adopting immersion cooling as a key strategy for improving energy efficiency and thermal management in data centers. Hence, ongoing research and development efforts need to be redirected to overcoming these remaining obstacles, thus paving the way for more energy efficient data center operations with reduced footprint for water and power consumption in the future; while also improving the sustainability, reliability, robustness, and resilience of these platforms.
more »
« less
- Award ID(s):
- 2401943
- PAR ID:
- 10654765
- Publisher / Repository:
- Begellhouse
- Date Published:
- Page Range / eLocation ID:
- 1513 to 1533
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The data center’s server power density and heat generation have increased exponentially because of the recent, unparalleled rise in the processing and storing of massive amounts of data on a regular basis. One-third of the overall energy used in conventional air-cooled data centers is directed toward cooling information technology equipment (ITE). The traditional air-cooled data centers must have low air supply temperatures and high air flow rates to support high-performance servers, rendering air cooling inefficient and compelling data center operators to use alternative cooling technology. Due to the direct interaction of dielectric fluids with all the components in the server, single-phase liquid immersion cooling (Sp-LIC) addresses mentioned problems by offering a significantly greater thermal mass and a high percentage of heat dissipation. Sp-LIC is a viable option for hyper-scale, edge, and modular data center applications because, unlike direct-to-chip liquid cooling, it does not call for a complex liquid distribution system configuration and the dielectric liquid can make direct contact with all server components. Immersion cooling is superior to conventional air-cooling technology in terms of thermal energy management however, there have been very few studies on the reliability of such cooling technology. A detailed assessment of the material compatibility of different electronic packaging materials for immersion cooling was required to comprehend their failure modes and reliability. For the mechanical design of electronics, the modulus, and thermal expansion are essential material characteristics. The substrate is a crucial element of an electronic package that has a significant impact on the reliability and failure mechanisms of electronics at both the package and the board level. As per Open Compute Project (OCP) design guidelines for immersion-cooled IT equipment, the traditional material compatibility tests from standards like ASTM 3455 can be used with certain appropriate adjustments. The primary focus of this research is to address two challenges: The first part is to understand the impact of thermal aging on the thermo-mechanical properties of the halogen-free substrate core in the single-phase immersion cooling. Another goal of the study is to comprehend how thermal aging affects the thermo-mechanical characteristics of the substrate core in the air. In this research the substrate core is aged in synthetic hydrocarbon fluid (EC100), Polyalphaolefin 6 (PAO 6), and ambient air for 720 hours each at two different temperatures: 85°C and 125°C and the complex modulus before and after aging are calculated and compared.more » « less
-
The rapid growth in data center workloads and the increasing complexity of modern applications have led to significant contradictions between computational performance and thermal management. Traditional air-cooling systems, while widely adopted, are reaching their limits in handling the rising thermal footprints and higher rack power densities of next-generation servers, often resulting in thermal throttling and decreased efficiency, emphasizing the need for more efficient cooling solutions. Direct-to-chip liquid cooling with cold plates has emerged as a promising solution, providing efficient heat dissipation for high-performance servers. However, challenges remain, such as ensuring system stability under varying thermal loads and optimizing integration with existing infrastructure. This comprehensive study digs into the area of data center liquid cooling, providing a novel, comprehensive experimental investigation of the critical steps and tests necessary for commissioning coolant distribution units (CDUs) in direct-to-chip liquid-cooled data centers. It carefully investigates the hydraulic, thermal, and energy aspects, establishing the groundwork for Liquid-to-Air (L2A) CDU data centers. A CDU’s performance was evaluated under different conditions. First, the CDU’s maximum cooling capacity was evaluated and found to be as high as 89.9 kW at an approach temperature difference (ATD) of 18.3 ◦C with a 0.83 heat exchanger effectiveness. Then, to assess the cooling performance and stability of the CDU, a low-power test and a transient thermohydraulic test were conducted. The results showed instability in the supply fluid temperature (SFT) caused by the oscillation in fan speed at low thermal loads. Despite this, heat removal rates remained constant across varying supply air temperatures (SATs), and a partial power usage effectiveness (PPUE) of 1.042 was achieved at 100 % heat load (86 kW) under different SATs. This research sets a foundation for improving L2A CDU performance and offers practical insights for overcoming current cooling limitations in data centers.more » « less
-
Abstract Data centers are critical to the functioning of modern society as they host digital infrastructure. However, data centers can consume significant amounts of energy, and a substantial amount of this energy goes to cooling systems. Efficient thermal management of information technology equipment is therefore essential and allows the user to obtain peak performance from a system and enables higher equipment reliability. Thermal management of data center electronics is becoming more challenging due to rising power densities at the chip level. Cooling technologies like single-phase immersion cooling allow overcoming many such challenges owing to their higher thermal mass, lower fluid pumping powers, and potential component reliability enhancements. It is known that immersion cooling deployments require extremely low coolant flow rates, and, in many cases, natural convection can also be used to sufficiently dissipate the heat from the hot server components. It, therefore, becomes difficult to ascertain whether the rate of heat transfer is being dominated by forced or natural convection. This may lead to ambiguity in choosing an optimal heat sink solution and a suitable system mechanical design due to unknown flow regimes, further leading to sub-optimal system performance. Mixed convection can be used to enhance heat transfer in immersion cooling systems. The present investigation quantifies the contribution of mixed convection using numerical methods in an immersion-cooled server. An open compute server with dual CPU sockets is modeled on Ansys Icepak with varying power loads of 115W, 160W and 200W. The chosen dielectric fluid for this single-phase immersion-cooled setup is EC-100. Steady-state Computational Fluid Dynamics (CFD) simulations are conducted for forced, natural, and mixed convection heat transfer in a thermally shadowed server configuration at varying inlet flow rates. A baseline heat sink and an optimized heat sink with an increased fin thickness and reduced fin count are utilized for performance comparison. The effect of varying Reynolds number and Richardson number on the heat transfer rate from the heat sink is discussed to assess the flow regime, stability of the flow around the submerged components which depends on the geometry, orientation, fluid properties, flow rate and direction of the flow. The dimensionless numbers’ influence on heat transfer rate from a conventional air-cooled heat sink in immersion versus an immersion-optimized heat sink is also compared. The impact of server orientation on heat transfer behavior for the immersion optimized heat sink is also studied on heat transfer behavior for the immersion optimized heat sink.more » « less
-
Abstract To fulfill the increasing demands of data storage and data processing within modern data centers, a corresponding increase in server performance is necessary. This leads to a subsequent increase in power consumption and heat generation in the servers due to high performance processing units. Currently, air cooling is the most widely used thermal management technique in data centers, but it has started to reach its limitations in cooling of high-power density packaging. Therefore, industries utilizing data centers are looking to singlephase immersion cooling using various dielectric fluids to reduce the operational and cooling costs by enhancing the thermal management of servers. In this study, heat sinks with TPMS lattice structures were designed for application in singlephase immersion cooling of data center servers. These designs are made possible by Electrochemical Additive Manufacturing (ECAM) technology due to their complex topologies. The ECAM process allows for generation of complex heat sink geometries never before possible using traditional manufacturing processes. Geometric complexities including amorphous and porous structures with high surface area to volume ratio enable ECAM heat sinks to have superior heat transfer properties. Our objective is to compare various heat sink geometries by minimizing chip junction temperature in a single-phase immersion cooling setup for natural convection flow regimes. Computational fluid dynamics in ANSYS Fluent is utilized to compare the ECAM heat sink designs. The additively manufactured heat sink designs are evaluated by comparing their thermal performance under natural convection conditions. This study presents a novel approach to heat sink design and bolsters the capability of ECAM-produced heat sinks.more » « less
An official website of the United States government

