It is becoming increasingly likely that a hybrid approach to server cooling will be needed inside an individual data center, with air and direct liquid cooling (direct-to-chip technology and immersion cooling) coexisting. With each data center championing their own system setup, there are some factors to consider when selecting the right glycol-based heat transfer fluid for your direct-to-chip liquid cooling racks.
1. Quality of Glycol
A key component of a superior heat transfer fluid is the quality of the glycol itself. Often glycols derived from bio-renewable sources, recycled, or even industrial grade glycols, can contain significant amounts of impurities such as ethylene glycol or diethylene glycol. These impurities can impact toxicity, impart strong odors, cause excessive foam, and reduce the life of the equipment they interact with. To achieve the best results for both heat transfer and fluid life, high-purity glycol is a necessity.
Every glycol-based fluid will degrade over time. This is natural and unavoidable but starting a system with impurities from the onset will lead to a reduction in fluid lifetime. With the push for server racks to operate for five to eight years, a high-quality product such as DOWFROST LC can last the lifetime of the equipment with little-to-no maintenance.
2. Corrosion Prevention
Another critical attribute of a high-performing heat transfer fluid is the additive package. The right inhibitor package is crucial to protect the metal components in your system. Not all inhibitor packages are created equal so you must ensure the fluid used is formulated with inhibitors that not only passivate the metals to eliminate corrosion risk and prevent fouling but also maintain stable conditions to allow for long fluid life.
In the case of direct-to-chip liquid cooling, a main feature of this system are the copper cold plates. As a consequence, an appropriate amount to of copper inhibitors need to be incorporated into the fluid. Certainly, systems can vary, and other materials of construction may be used in addition to just copper. Be sure to check the fluid compatibility with other components, as well as metals protection through the inhibitor package.
3. Water Quality
Overall performance, fluid stability and system integrity are all affected by the quality of the dilution water being used. The best way to avoid the issues caused by poor water is to purchase pre-diluted or ready-to-use fluid that is already formulated to your specified concentration (e.g., 25% propylene glycol). If this is not an option, a concentrated heat transfer fluid should always be diluted with a high-quality water, free of troublesome salts, ions and impurities, to a concentration no less than 25% glycol. Impurities in dilution water can increase metal corrosion, aggravate pitting of cast iron and steel, reduce the effectiveness of corrosion inhibitors, increase inhibitor depletion rate, cause formation of scale and other deposits on heat transfer surfaces, and cause clogging of system components. Distilled or deionized water is typically recommended for use when diluting.
4. Fluid Maintenance and Testing
There is a great deal that must be considered when formulating and selecting the right heat transfer fluid for your system, such as corrosion protection, compatibility with system components and fluid life. One of the best ways to take full advantage of these benefits is to perform routine monitoring. In most cases, there are simple on-site tests to ensure that your fluid is in a healthy state and the system is operating properly (e.g., fluid pH, reserve alkalinity, refractive index). However, it is recommended that a comprehensive analysis be completed at least once per year by the manufacturer or at an external lab. A full analysis will indicate if fluid parameters are outside of specifications or if there are corrosion risks within the system. Any deviations from acceptable criteria should be mitigated by addition of inhibitors, boosters, or additional fluid.
Acceptable fluid criteria should be readily available by the manufacturer and used as a guide to keep your system protected and operating within recommended limits. For questions related to testing and maintenance of DOWFROST LC Heat Transfer Fluid, feel free to reach out to Dow's Technical Service representative or refer to the Open Compute Project’s white paper on Guidelines for Using Propylene Glycol Heat Transfer Fluids.
Jordan Rau is the North American Marketing Manager at Dow Inc. for Heat Transfer Fluids. Connect with Jordan on LinkedIn. Discover more about the DOWFROST LC Heat Transfer Fluid here or visit the webpage for more information.