Comparison of Dielectric Fluids for Immersive Liquid Cooling of IT Equipment

Overview

The paper compares the two fluid families used in immersion cooling: hydrocarbon oils (mineral, synthetic, bio-based) and fluorocarbons (used in single- and two-phase systems). The comparison covers TCO, material compatibility, safety (flash point, toxicity), environmental impact, and IT maintenance and handling. Synthetic oils are cheap and benign but make servicing messy; fluorocarbons evaporate cleanly and are compatible with more materials, but cost more.

The numbers: hydrocarbon fluid flash points run from about 115 C for mineral oil to more than 200 C for synthetics (one example 268 C). Fluorocarbon boiling points range from about 50 C for two-phase use to about 270 C for single-phase use. Single-phase immersion dielectric typically operates at about 50 to 60 C, reaching the OSHA touch-safety threshold of 60 C at the high end. Sealed two-phase systems can lose about 1 to 2% of fluid (evaporation) per year.

Regulatory risk is decisive. Many fluorocarbons are PFAS; 3M's announced exit from all PFAS manufacturing by the end of 2025, and emerging EU and US restrictions, are named as the key risks for two-phase systems. Fluoroketones can have a GWP below 1. On fire safety, a flash point above 93 C gives a lower NFPA 704 flammability rating, and the paper advises engaging the local AHJ.

Key points

1. Hydrocarbon immersion fluids: flash point from about 115 C (mineral oil) to more than 200 C (synthetic); one example 268 C.
2. Fluorocarbon boiling points range from about 50 C (two-phase use) to about 270 C (single-phase use).
3. Single-phase immersion dielectric typically operates at about 50 to 60 C, reaching the OSHA touch-safety threshold of 60 C at the high end.
4. Sealed two-phase systems can lose about 1 to 2% of fluid (evaporation) per year.
5. Fluoroketones can have GWP below 1, but many fluorocarbons are PFAS; 3M announced exit from all PFAS manufacturing by end of 2025.
6. NFPA 704: a flash point above 93 C gives a lower flammability rating; engage the local AHJ.

Using it in design

• Add a dielectric-fluid catalog with family (hydrocarbon, fluorocarbon), phase (1p, 2p), flash point, boiling point, GWP, PFAS status, cost per litre and annual loss percentage.
• In fire and compliance checks, flag hydrocarbon fluids with a flash point below 93 C for AHJ review and NFPA 704 labelling.
• Flag PFAS fluids with a regulatory-risk warning.
• In the O&M module, add servicing-time and drip-tray requirements for oil immersion.

Who should read it

Engineers selecting fluids for immersion cooling, fire and environmental compliance owners, and operations teams.

Related standards

• NFPA 704
• NFPA 75
• EU PFAS restriction proposal (ECHA)
• ASHRAE TC9.9 Liquid Cooling Guidelines

Publication details

Authors

Robert Bunger; Paul Lin

Publisher

Schneider Electric

Year

2023

Document number

WP 291

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation