Oils STILL ain't Oils
In this article, we explore the world of immersion fluids used in cooling systems.
Optimal performance, heat transfer efficiency, and system longevity hinge upon the selection of the most suitable immersion fluid. Attributes like high thermal conductivity, low viscosity, and exceptional dielectric properties are non-negotiable in ensuring effective heat removal.
As discussed in a previous article (Oils ain't Oils | LinkedIn), there are two methods in deploying immersion cooling, being single- or two-phase architectures, and a quick summary below;
In single-phase immersion cooling, the liquid remains in a liquid state throughout the cooling process. The heat from the electronic components is transferred to the liquid through conduction. The liquid is then cooled by a heat exchanger or other cooling system.
In two-phase immersion cooling, the liquid boils to a vapor as it absorbs heat from the electronic components. The vapor then condenses back to a liquid on a heat exchanger, releasing the heat to the cooling system.
When it comes to what actually goes into those tanks, it's important to understand that each type of cooling, requires a different fluid solution.
Single Phase Fluids
Phase State: Single-phase immersion cooling fluids remain in a liquid state throughout the cooling process. They do not undergo phase changes like boiling or vaporization.
Boiling Point: Single-phase cooling fluids typically have higher boiling points compared to two-phase fluids. This means they operate at lower temperatures, which can be beneficial for certain applications where avoiding high temperatures is crucial.
Flash Point: Single-phase fluids usually have higher flash points, making them less prone to combustion or flammability risks. This can enhance safety in cooling systems.
Viscosity: Single-phase cooling fluids generally have higher viscosities compared to two-phase fluids. Higher viscosity can influence flow characteristics and may require different pump and circulation system designs.
Heat Transfer: Heat transfer in single-phase immersion cooling is primarily convective, where the fluid carries heat away from the immersed components. While this is efficient, it may not provide the extreme cooling potential of boiling fluids.
Fluid suppliers include the big oil players (Chevron, Shell, and bp/Castrol) however you might be surprised that companies like Cargill, a bio-industrial group of large food, agriculture and industrial products, also manufacture an immersion fluid.
Fuchs, well known for their performance oil in motor-racing, produce their own dielectric fluid, as do Lubrizol, the folks that make, amongst other things, your hand sanitizer, produce a fluid called CompuZol.
Two Phase Fluids
Phase State: Two-phase immersion cooling fluids can undergo phase changes, transitioning between liquid and vapor phases. This phase change absorbs a significant amount of heat, providing efficient cooling.
Boiling Point: Two-phase cooling fluids have lower boiling points, which means they can operate at higher temperatures compared to single-phase fluids. This can be advantageous for applications where high heat dissipation is required.
Flash Point: Two-phase fluids often have lower flash points, making them potentially more flammable. Proper safety measures are crucial when using such fluids.
Viscosity: Two-phase cooling fluids typically have lower viscosities than single-phase fluids. This lower viscosity can facilitate better natural convection and heat transfer.
Heat Transfer: Heat transfer in two-phase immersion cooling is more efficient due to the phase change. As the fluid vaporizes and condenses, it can dissipate heat more effectively, even in extreme thermal scenarios.
Two-phase immersion solutions have historically relied on a 3M product (Novec or Fluorinert. Typically a low-boiling point target, and historically containing PFAS, discussion around immersion cooling become more mainstream many years ago, as Alibaba Cloud and Tencent publicly demonstrated solutions, with significant Wiwynn involvement.
Alibaba has been using immersion cooling technologies (including two-phase) since at least 2017, and joined the Open Compute Project (OCP) the same year to promote the benefits and share progress.
Alibaba is developing its own immersion cooling tech - DCD (datacenterdynamics.com)
A recent development from Feb 2023, is that Alibaba Cloud has announced they are working with Shell on testing their immersion fluids, suggesting they are focussing on single-phase going forward.
Alibaba Cloud to test Shell China's cooling fluid - DCD (datacenterdynamics.com)
A note about PFAS
Per- and Polyfluroroalkyl substances (PFAS) are long lasting chemicals, which break down very slowly over time. Popularized and widely deployed in Teflon based products like frypans, due to Teflon's non-stick, stain repellent and waterproof properties, PFAS have been linked to cancer and other diseases.
Patented by DuPont (and if you haven't seen Dark Waters with Mark Rufflo, you really should!) Teflon was manufactured by 3M for decades.
3M's fluid solutions have been used in many two-phase immersion designs, however, the conversation around immersion cooling took a turn when 3M announced its exit from PFA manufacturing, which meant that its Novec and Fluorinert products would be discontinued by 2025. This prompted the search for alternative fluids to sustain operations.
Chemours has developed a solution (Opteon SF33), and developing an updated product called Opteon 2P50 is designed for two-phase cooling systems, which is in testing and plans to bring to market in 2025, though it is unclear if these solutions will meet specific criteria needed to be a drop-in replacement for 3M's products, or have PFAS adjacent issues.
The repercussions of PFAS have extended beyond immersion cooling, as evidenced by the $1.185 billion settlement fund established by Chemours, DuPont, and Corteva to address PFAS-related drinking water claims.
Chemours, DuPont, and Corteva Reach Comprehensive PFAS | CC Stock News (stocktitan.net)
Fluids ain't fluids?
Immersion fluids are pivotal in efficiently managing the high heat generated by cutting-edge infrastructure. The choice between single-phase and two-phase immersion cooling hinges on the specific requirements of each application. Choosing a fluid vendor and type comes down to application, with many immersion technology companies working closely with fluid vendors to modify and tweak the chemical properties specific for their use case.
As innovation, fluid dynamics, and compliance converge, the evolution of immersion cooling fluids promises a resilient future for heat management in the data center industry.
Want to contribute?
The OCP community has a great work stream specifically for cooling, discussing warranties, material compatibility and more, which is a great resource and the team is always looking for contributors, if interested.