Detailed Explanation of Coolant Technology Knowledge
Coolant is a commonly used heat exchange medium in liquid cooling systems, which restores equipment to normal operating temperatures through heat exchange. For cold plate liquid cooling systems, secondary-side coolants typically include water-based and non-water-based types. The selection must not only meet cooling performance requirements but also ensure compatibility and long-term reliability with all wetted materials in the secondary-side cooling loop. Additionally, comprehensive factors such as the convenience of IT equipment and coolant maintenance, expected service life, and liquid cost should be considered.
Comparison of Advantages and Disadvantages of Different Types of Coolants
1. Water
Advantages:Excellent heat transfer performance and fluidity, maintenance-free for life, stable quality, with simple and easy-to-monitor indicators.
Disadvantages:After leakage for a certain period, conductivity may increase, potentially causing short circuits in IT equipment; the recirculating cooling system must include a deionization device; the use of formulated liquid may lead to increased conductivity, with varying quality levels across different brands.
2. Glycol-based antifreeze
Advantages:>25% (by volume) glycol can inhibit bacterial growth and is suitable for use in environments below freezing point.
Disadvantages:The increase in liquid viscosity leads to higher pump power consumption; as the glycol content rises, the heat dissipation performance decreases; prolonged operation causes glycol oxidation, producing highly corrosive substances such as formic acid and acetic acid.
3. Dielectric liquid
Advantages:Low conductivity, preventing potential short circuits in electronic devices after leakage.
Disadvantages:High density, low specific gravity and specific heat; relatively high cost; some liquids require consideration of GWP impact; potential for flow instability and uneven distribution in two-phase microchannel cold plates.
4. Refrigerant
Advantages:Higher latent heat, lower pump power consumption, can be inert (non-toxic/non-flammable/non-conductive).
Disadvantages:The operating pressure is typically higher than that of single-phase liquids and dielectric liquids; there is a possibility of flow instability and uneven distribution in two-phase microchannel cold plates; certain coolants require consideration of ODP and global warming potential (GWP) impacts.
Recommendations for the use of pure ethylene glycol and its aqueous solutions
Pure ethylene glycol and its aqueous solutions are highly corrosive to carbon steel, copper, aluminum, and non-ferrous metals such as solder. Ethylene glycol contains intramolecular and intermolecular hydrogen bonds, with active hydrogen and hydroxyl groups prone to oxidation. Over prolonged use, pure ethylene glycol and its aqueous solutions gradually oxidize, producing various byproducts such as glycolaldehyde, glyoxal, glycolic acid, oxalic acid, formic acid, acetic acid, and other acidic substances. These can cause severe corrosion to critical components of equipment, pipelines, and valves made of carbon steel, copper, aluminum, tin, and other non-ferrous metals.
Moreover, pure ethylene glycol itself is a relatively reactive substance. When polymerized in solution to form high-molecular-weight compounds, it further oxidizes into polymeric organic acids, becoming a highly viscous and dense material. After deposition, it tends to form scale, which is also the primary reason for the increased acidity of the solution. Deteriorated ethylene glycol aqueous solutions not only reduce the heat transfer coefficient but also increase the system's energy consumption.
During use, ethylene glycol aqueous solution is prone to generate bubbles when in contact with air. The micro-jets or shock waves produced during bubble collapse cause damage to equipment—known as cavitation (also called gas erosion or cavitation erosion). The cavitation phenomenon initially manifests as discoloration, with localized areas turning gray-white, then gradually becoming rougher, followed by the appearance of pitting and needle holes that deepen over time. Eventually, this leads to spalling or the formation of clustered honeycomb-like cavities, which can severely penetrate the equipment. Additionally, due to the unevenness of the metal surface, countless tiny cavity clusters accumulate, ultimately resulting in corrosion perforation and leakage on the metal surface.
Therefore, when using ethylene glycol aqueous solution, an appropriate amount of compound additives must be employed. These additives can inhibit corrosion and swelling of metals and non-metallic materials in contact during system operation, prevent scale formation, avoid pipeline blockages, stop bacterial growth, suppress discoloration and odor of the ethylene glycol solution, and control foam generation.
The compound agent requires the assistance of oxygen in the liquid to oxidize and form a film on the inner metal surface, achieving corrosion prevention by inhibiting the anodic process of the corrosion reaction. Chloride ions, high temperatures, and high-speed water flow can all damage the oxide layer, necessitating regular replenishment.
Selection and Application of Coolant
When selecting a coolant, it is essential to comprehensively consider factors such as the operating environment temperature, equipment material compatibility, heat transfer performance requirements, maintenance costs, and safety. Proper selection and use of coolant not only ensure the normal operation of equipment but also effectively extend its service life and reduce maintenance costs.
For different application scenarios, the most suitable coolant product should be selected based on specific usage conditions and requirements. In practical applications, it is recommended to consult professional technical personnel to ensure the correct selection and use of coolant.