How to Choose the Right Fluid for Cold Plate

Liquid cooling systems transfer heat four times better than the same mass of air. And the cold plate takes up less space, which allows it to provide higher performance cooling for smaller systems. Liquid Cold plates can replace space-consuming radiators and fans.

As manufacturing capabilities improve, the cost and leakage of cold plates are no longer a significant concern. Many people prefer to choose a liquid cooling solution when choosing a cooling solution for their equipment when the option is available, so the main question now is "which fluid should we use?"

For liquid-cooled panels, the choice of working fluid is as vital as choosing the hardware. The wrong fluid can lead to poor heat transfer, clogging, and even system failure. The proper heat transfer fluid should provide compatibility with the system metals, high thermal conductivity, specific heat, low viscosity, low freezing point, high flash point, low corrosion, low toxicity, and thermal stability.

Today, despite many improvements in liquid cold plate designs, the choice of coolants is still relatively limited. In many cases, plain water will suffice, but when it comes to specific special equipment that may require higher heat dissipation, other more suitable coolants are considered.

Basic Cooling Options

While water provides excellent cooling performance in cold plates, it is not always practical due to its low freezing temperatures. Additives such as glycol are often required to alter the properties of the coolant better to suit the operating environment of the cold plate.

Temperature range requirements are a significant consideration for cold plate fluids. Some fluids freeze at temperatures below water but have a low heat transfer capability. The fluid selected must also be compatible with the internal metal of the cold plate to limit any potential corrosion.

The coolants fluid commonly used in liquid cold plates today are:

• Water

• Deionized water

• Inhibited glycol and aqueous solutions

• Dielectric fluids

Water

Water has a very high heat capacity and thermal conductivity. It is compatible with copper and can be considered one of the best heat transfer materials for use in fluid paths. Facility water or tap water may contain impurities that can cause corrosion or clog fluid paths in the fluid cooling circuit. Therefore, it is recommended that high-quality water be used to minimize corrosion and optimize thermal performance. Suppose you determine that your facility water or tap water contains a large percentage of minerals, salts, or other impurities. In that case, you can filter the water, or you can choose to purchase filtered or deionized water.

Deionized water

Through the deionization process, we can remove the harmful minerals, salts, and other impurities that can cause corrosion or scaling. Deionized water has a high resistivity compared to tap water and most fluids. Deionized water is an excellent insulator for the manufacture of electrical components where the parts must be electrically isolated. However, as the resistivity of water increases, so does its corrosivity. If you want to use deionized water in cold plates or heat exchangers, we will recommend stainless steel tubing.

Inhibited glycol and Water Solutions

Ethylene glycol + water (EGW) and propylene glycol + water (PGW) are the two types of glycols most commonly used in liquid cooling applications. Ethylene glycol has desirable thermal properties, including a high boiling point, low freezing point, stability over a wide temperature range, and high specific heat and thermal conductivity. It also has a low viscosity, thus reducing pumping requirements. Although EGW has more desirable physical properties than PGW, PGW is used in applications where toxicity may need to be considered. PGW is generally considered safe for food or food processing applications and can also be used in confined spaces.

Dielectric fluids

Dielectric fluids are non-conductive and are therefore preferred over water when working with sensitive electronic equipment. Perfluorocarbons, over a wide range of operating temperatures 3M's dielectric fluid Fluorinert™ are non-flammable, non-explosive, and thermally stable, and Fluorinert™ is less corrosive than deionized water. Although deionized water is also non-conductive, However, it has a much lower thermal conductivity and is much more expensive. PAO is a synthetic hydrocarbon used for its dielectric properties and wide range of operating temperatures. For example, fire control radars on today's jet fighters use PAO for liquid cooling. To test cold plates and heat exchangers that will use PAO as a heat transfer fluid, PAO-compatible recirculating coolers can be used. Like perfluorocarbons, PAO has a much lower thermal conductivity than water.

Conclusion

Water, deionized water, glycol/water solutions, and dielectric fluids(fluorocarbons and PAO) are the most common heat transfer fluids used in high-performance liquid cooling applications. As to which one should be used, we need to choose the most suitable coolant in conjunction with the specific cold plate material to be used and to see what level of cooling capacity the equipment needs to achieve.

Suppose you are interested in learning more about the types of cold plates available. In that case, you can view the various types of cold plate designs in our product section "Liquid Cold Plate," You can also learn more about our Liquid cold plate service through our "Liquid Cooling Solution."