Immersion Cooling is a highly efficient heat dissipation technology that achieves heat exchange by immersing the heat generating device directly in an insulating coolant. Silicone oil has become one of the core cooling media in this field due to its unique physical and chemical properties. The following are the characteristics, types and selection points of immersion cooling silicone oil:
Core characteristics of immersion cooling silicone oil
Insulation performance
Volume resistivity: >10<sup>15</sup> Ω·cm (GB/T 1410), completely isolates current, suitable for high-voltage equipment (such as GPU/transformer).
Dielectric strength: >30 kV/2.5mm (ASTM D877), avoids circuit short circuit.
Thermophysical properties
Parameter Typical value Comparison (mineral oil)
Thermal conductivity 0.15~0.18 W/(m·K) 0.12 W/(m·K)
Specific heat 1.5~1.8 kJ/(kg·K) 1.9 kJ/(kg·K)
Flash point >250℃ 160~200℃
Chemical stability
Oxidation resistance: Long-term viscosity change at 200°C <±5% (ISO 3448).
Compatibility: Does not corrode metals such as copper and aluminum, and is compatible with common sealing materials (such as EPDM and fluororubber).
Common silicone oil types and applicable scenarios
Dimethyl silicone oil (PDMS)
Viscosity range: 5~1000 cSt (low viscosity for high flow rate, high viscosity for sealing system).
Advantages: low cost (about ¥150/kg), strong compatibility.
Disadvantages: low thermal conductivity, need to add nanoparticles (such as Al<sub>2</sub>O<sub>3</sub>) to enhance.
Application: immersion cooling of data center servers, heat dissipation of LED driver power supply.
Phenyl silicone oil
Features: The introduction of benzene ring improves high temperature resistance (long-term use temperature > 180°C).
Applicable scenarios: Electric vehicle battery packs, high-power IGBT module cooling.
Fluorinated silicone oil
Advantages:
Flammability (oxygen index > 90%, UL94 V-0).
Foul resistance (repels dust and moisture).
Disadvantages: Expensive (> ¥2000/kg).
Applications: Aerospace electronic equipment, military radar cooling.
Key selection indicators
Viscosity-heat dissipation efficiency balance
Low viscosity (5~50 cSt): low pumping energy consumption, suitable for forced convection system.
High viscosity (100~1000 cSt): reduce leakage risk, suitable for passive cooling.
Temperature adaptability
Low temperature start: -40℃ viscosity <5000 cSt (avoid solidification).
High temperature stability: volatile matter <0.1% at 150℃.
Additive compatibility
Antioxidants (such as BHT): extend service life.
Nanofillers: can increase thermal conductivity to 0.25 W/(m·K) (add 5% AlN).
Typical application cases
Bitcoin mining machine cooling
Using 50 cSt dimethyl silicone oil, the temperature of the mining machine chip dropped from 95℃ to 55℃, and the energy consumption was reduced by 35%.
Transformer immersion cooling
Phenyl silicone oil (500 cSt) replaced mineral oil, the heat dissipation efficiency was increased by 20%, and the fire protection level reached K3.
Maintenance and safety
Monitoring indicators:
Regularly test the acid value (>0.1 mg KOH/g requires replacement).
Water content (Karl Fischer method, required to be <50 ppm).
Waste liquid treatment:
Silicone oil can be filtered and regenerated (such as using molecular sieves to absorb impurities), and waste liquid is treated as HW08 hazardous waste.
Immersion cooling silicone oil needs to be selected based on the system design temperature, flow rate requirements and cost budget:
General scenario: dimethyl silicone oil (best cost performance);
High temperature/fire protection requirements: phenyl or fluorinated silicone oil;
Extreme heat dissipation: nanofluid modified silicone oil.
Note: In actual applications, the compatibility of silicone oil and equipment materials needs to be verified (such as preventing silicone oil from dissolving plastic cable coatings).
