Liquid Cooling and the Chemical Compatibility Imperative

Understanding coolants and components’ materials of construction — and their interaction

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Power densities in electronic subsystems continue to increase, driving demand for more extreme cooling power – cooling power such as that available with liquid cooling. Now more than ever to optimize thermal management efficiency, sustainability and reliability, designers of systems that use liquid cooling are exploring innovative combinations of component materials, including advanced thermoplastics, specialized elastomers, metal alloys and engineered fluids.

Whether designing a closed-loop, single-phase immersion, two-phase immersion or direct-to-chip cooling system, component material compatibility is critical to performance. This tech guide provides general guidance regarding selecting the right ingredients for your liquid cooling solution.

Think Holistically When Selecting Components

A variety of subsystems and components make up the architecture that is critical to the successful and reliable operation of any cooling system.

Each system component has the potential for interaction with other component materials. Therefore, materials interactions and dependencies warrant detailed analysis during design and specification.

Coolants are of particular interest, not only as the primary conduit of thermal transfer, but because they are in contact with all wetted materials within a particular cooling system and essentially “connect” all components. Some fluids may promote corrosion or biofouling in the presence of certain materials, creating the potential for impedance in or failure of the cooling system. Therefore, it’s essential to understand what all the materials are and the interactions that they might have. Specifically, when assessing chemical compatibility, potential permeation or diffusive losses, identify critical points of connection – such as tubing junctions, manifold ports, and quick disconnect fittings – and evaluate each one for risks to reliability and performance.

Overall, when it comes to material selection, think holistically. Take into account all system components, and consider potential effects of the environment, working fluid, temperature, pressure, and mechanical loading, which might adversely impact performance.

In this tech guide, we’ll take a look at coolants commonly used in liquid cooling applications and provide an overview of the materials of construction. Finally, we’ll provide guidance regarding the potential compatibility of these fluids and materials when used together.

Download tech guide PDF now and get material and coolant compatibility quick reference matrix.

Tapping Coolant Alternatives

Obviously, choosing a coolant is a focal point when designing a liquid cooling system. From a compatibility standpoint, it’s important to recognize that the fluid links virtually every component as it circulates through the liquid cooling system. See the Coolants table for a brief overview of a number of fluids typically used in cooling electronics.

Start by looking at operating and storage temperatures. Identify fluids with properties appropriate to your application environment, such as a boiling point that satisfies the thermal load and thermal efficiency needed without exceeding the critical heat flux. Check low temperature characteristics during storage and shipping, environmental exposures, particularly with engineered dielectrics such as fluorochemicals, as well as refrigerants. It’s often necessary to understand the environmental impact of the fluid throughout the life cycle – how it’s manufactured, the potential impact of it leaching into the facility or atmosphere during use, and end-of-life fluid reclamation requirements.

Coolants

When selecting fluids consider the ozone depletion and global warming potentials, in particular with regard to refrigerants and dielectrics. Over the last decade or so, the World Health Organization guidelines have increased emphasis on these parameters, prompting the development of greener alternatives, such as 3M Novec, HFE coolant, and more environmentally friendly, fourth generation hydrofluoroolefin refrigerants like R-1234 or R-1336.

In addition to thermal stability and chemical compatibilities, consider coolant toxicity, flammability, cleanliness requirements, environmental impact, and cost. And of course, when comparing coolant types and options, make sure to consider all materials that the fluid may come in contact with throughout the system.

Sizing Up Materials of Construction

Electronics cooling system components are, in general, comprised of three types of polymers – commodity plastics, engineered thermoplastics, and elastomers – and four types of metal alloys – aluminum, brass, copper and stainless steel. The information below provides a high-level comparison of liquid cooling system component materials of construction.

Polymer strengths
Polymer limitations
Elastomers
Metal alloys

Putting It All Together: Chemical Compatibility

With a foundational understanding of the fluids, plastics and metals that might be employed in a given liquid cooling application, we can assess potential chemical compatibility of system components, based on their make-up, to ensure reliable, long term operation.

While polymers and metals can be effective in any combination when appropriately specified, it is critical to distinguish…

https://cpcworldwide.com/Portals/0/Library/Resources/Literature/Guides/CPC%20-%20Chemical%20Compatibility%20Tech%20Guide.pdf
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