Selection Guide · 2026-09-27
Immersion Cooling Fluids: Silicone vs Synthetic Hydrocarbons
Technical comparison guide for single-phase immersion cooling fluids. Compare kinematic viscosity, dielectric strength, flash point, and compatibility.
Key takeaways
- Kinematic viscosity directly governs pumping parasitic load: low-viscosity synthetic fluids (such as Eurotherm ICF-EV4 at 2.1 mm²/s at 40°C) and polysiloxanes (such as Eurotherm Si-05 at 4 mm²/s) minimize flow resistance in forced circulation loops.
- Electrical dielectric integrity: specialized immersion coolants exhibit electrical conductivity below 0.1 pS/m and breakdown voltages between 39.4 kV and 45 kV, meeting the electrical isolation requirements of energized electronics.
- Thermal and safety operating ranges: installations prioritizing safety margins can evaluate high-flash-point synthetic fluids with open-cup flash points above 240°C (such as Eurotherm ICF-EV3, operating from -20°C to 330°C), while polysiloxanes provide pour points down to -90°C.
- Standard industrial thermal oils cannot substitute for dedicated dielectric coolants due to lack of ionic purification, unverified breakdown voltage, and potential elastomeric degradation.
Evaluation Criteria for Single-Phase Dielectric Liquids: Theory to Field Practice
In single-phase immersion liquid cooling architectures, heat-generating electronic components are placed in direct contact with a dielectric liquid, transferring thermal energy through fluid convection to an external heat rejection loop. While academic laboratory studies frequently evaluate natural convection heat transfer coefficients in quiescent fluid baths, commercial computing clusters and battery energy storage modules rely primarily on forced pumped circulation. Consequently, fluid selection must examine kinematic viscosity across the entire operating temperature curve rather than relying solely on static thermal conductivity.
Electrical insulation integrity presents an equally critical engineering boundary. Dielectric fluids must sustain high dielectric breakdown strength and long-term chemical inertness. Any fluid degradation resulting in ionic formation, elevated acid numbers, or moisture absorption can degrade insulation thresholds, increasing the risk of leakage currents or component failure in live electronic systems.
Fluid Chemistry Profiles: Polysiloxane vs Synthetic Hydrocarbons
Contemporary immersion cooling implementations predominantly utilize polysiloxanes (silicone chemistries) and synthetic single-phase hydrocarbons (such as polyalphaolefin or specialized synthetic cuts). Globally, these approaches run parallel to chemistries like DOWSIL ICL-1000 fluid or Shell Immersion Cooling Fluid lines. Polysiloxanes exhibit low surface tension, broad operating thermal windows, and dependable low-temperature fluidity. Synthetic hydrocarbons offer predictable dielectric constants, stable breakdown voltage retention, and good mechanical lubrication for circulating pumps.
Matching a dielectric fluid to a system requires aligning mechanical sealing configurations with operational thermal thresholds. The following table summarizes technical parameters for Chemie Eurotherm dielectric immersion and low-viscosity heat transfer media to support engineering evaluations.
| Product Model | Chemical Chemistry | Operating Range (°C) | Kinematic Viscosity @40°C (mm²/s) | Pour Point (°C) | Flash Point (Open Cup, °C) | Electrical / Dielectric Profile | System Design |
|---|---|---|---|---|---|---|---|
| Eurotherm ICF-EV4 | Synthetic single-phase coolant (low viscosity) | -50 to 250 | 2.1 | <-60 | 108 | Breakdown voltage 45 kV, high insulation | Closed system (nitrogen / cold-oil blanket) |
| Eurotherm ICF-EV1 | Synthetic single-phase coolant (hydrocarbon base) | -50 to 150 | 6 (5-7) | -60 | >150 | Conductivity <0.1 pS/m, high insulation | Closed system (nitrogen / cold-oil blanket) |
| Eurotherm ICF-EV2 | Synthetic single-phase coolant (hydrocarbon base) | -50 to 150 | 12 (10-15) | -60 | >190 | Conductivity <0.1 pS/m, oxidation resistant | Closed system (nitrogen / cold-oil blanket) |
| Eurotherm ICF-EV3 | Synthetic single-phase coolant (wide range) | -20 to 330 | 31 | <-60 | >240 | Dielectric strength 39.4 kV, boiling point >400°C | Closed system (nitrogen / cold-oil blanket) |
| Eurotherm Si-05 | Polysiloxane (silicone oil) | -80 to 280 | 4 | -90 | >128 | Odorless, non-corrosive, ultra-low temp flow | Open or closed systems (suggested <=150°C for open) |
| Eurotherm Si-10 | Polysiloxane (silicone oil) | -60 to 300 | 7.9 | -80 | >200 | Low volatility, thermal stability | Open or closed systems (suggested <=150°C for open) |
Viscosity, Dielectric Strength, and Material Compatibility Trade-offs
Viscosity serves as a governing hydrodynamic variable. Eurotherm ICF-EV4, for example, features a kinematic viscosity of 2.1 mm²/s at 40°C and maintains 27 mm²/s at -40°C. This low flow resistance enables uniform turbulent flow through dense server chassis or compact battery cell channels, keeping pressure drops and auxiliary pump power consumption low. Conversely, where fire protection standards demand higher flash margins, Eurotherm ICF-EV3 provides an open-cup flash point above 240°C and an initial boiling range exceeding 400°C, accompanied by a 40°C viscosity of 31 mm²/s requiring corresponding pump head planning.
Material compatibility is an equally critical parameter for long-term field reliability. Silicone fluids generally show inert behavior toward most microelectronic polymers and board laminates, but they can induce swelling in standard silicone rubber gaskets and seals. Synthetic hydrocarbons are typically compatible with fluoropolymer seals (such as FKM/PTFE) but require systematic testing against ethylene propylene diene monomer (EPDM), certain polyurethanes, and flexible PVC cabling. Engineers should confirm chemical resistance data prior to final hardware specification.
Why Standard Industrial Heat Transfer Oils Cannot Serve as Immersion Coolants
A common misconception is that standard thermal fluids can be repurposed for immersion cooling based solely on generic base oil categories. Traditional heat transfer oils are formulated for closed industrial pipe circuits focusing on thermal cracking resistance and anti-coking properties at elevated bulk temperatures. They are not subjected to semiconductor-grade drying and ionic purification routines, and they may contain polar additive packages that compromise electrical resistivity.
When unpurified industrial oils are introduced into energized systems, residual trace ions and moisture can migrate along electric field lines, accelerating dielectric breakdown and causing leakage currents. Purpose-engineered immersion fluids, such as the Eurotherm ICF series, undergo targeted treatment to maintain electrical conductivity below 0.1 pS/m and dielectric breakdown voltages above 35 kV, ensuring stable operation within energized electronic environments.
Engineering Selection Recommendations and Local Technical Support
For high-density computing and server racks operating within closed nitrogen-blanketed loops, low-viscosity media such as Eurotherm ICF-EV4 or ICF-EV1 offer balanced thermal transport with low parasitic pumping overhead. In applications where elevated thermal safety margins or broad temperature limits are specified, Eurotherm ICF-EV3 provides an open-cup flash point above 240°C. For semiconductor test equipment (Chiller-Heater units) or open test baths requiring ultra-low-temperature circulation down to -80°C, the polysiloxane chemistry of Eurotherm Si-05 provides dependable fluid mobility with its -90°C pour point.
Design engineers can model operating parameters using the Chemie Online Fluid Selection Tool (calculator.szchemie.com.cn/select) or the AI Fluid Advisor (calculator.szchemie.com.cn/ai). Technical specialists at Suzhou Chemie Heat Transfer Technology Co., Ltd. are available to review system temperature curves, fluid-elastomer compatibility lists, and routine fluid monitoring schedules.
FAQ
How does kinematic viscosity influence immersion cooling system performance?
Kinematic viscosity directly determines the Reynolds number and hydraulic pressure drop across restricted flow paths. Lower viscosity fluids, such as Eurotherm ICF-EV4 at 2.1 mm²/s at 40°C, reduce boundary layer thickness and promote efficient heat transfer while minimizing circulation pump parasitic power.
Why do synthetic hydrocarbon coolants generally require closed-loop configurations?
Synthetic hydrocarbon fluids exposed to ambient atmospheric air at elevated temperatures can experience oxidative degradation over time, forming peroxides or organic acids that impair electrical insulation. Utilizing a closed loop with a dry nitrogen or cold-oil blanket isolates the coolant from oxygen and moisture.
Can silicone dielectric fluids (such as Si-05) be blended with synthetic hydrocarbons (such as ICF-EV1)?
Blending silicone fluids with synthetic hydrocarbons is not recommended. Because of their differing molecular structures and solubility parameters, mixing can result in phase separation, cloudiness, shifted dielectric constants, and unpredictable interactions with system elastomers.
What indicators determine when immersion cooling fluids need purification or replacement?
Fluid condition should be verified by monitoring breakdown voltage, volume resistivity, moisture content, acid number, and 40°C kinematic viscosity. A noticeable drop in dielectric strength or an increase in conductivity indicates the need for filtration, dehydration, or fluid replacement.
What are the primary operating differences between Eurotherm Si-05 and Si-10?
Eurotherm Si-05 features a lower kinematic viscosity of 4 mm²/s at 40°C and a pour point of -90°C, designed for ultra-low-temperature cooling (-80°C to 280°C). Eurotherm Si-10 has a viscosity of 7.9 mm²/s at 40°C and an open-cup flash point above 200°C, suitable for operating ranges from -60°C to 300°C.
Sources
Product data are typical laboratory values for reference only; please confirm with a Chemie engineer.