Single-phase immersion cooling: how to write a dielectric-fluid specification that survives procurement

In single-phase immersion the fluid stays liquid throughout: heat is carried from the components into the bath, then out through a circulation loop and an external heat exchanger. Compared with two-phase designs it avoids refrigerant-style top-up and keeps the fluid chemistry simple, which is why it dominates retrofits and most new deployments in China.

The property set that matters: dielectric strength and volume resistivity for the electrical margin; kinematic viscosity at 25–60 °C because it sets pump power and flow distribution; flash point and fire behaviour for the facility risk file; volatility for top-up rate; and for European sites, GWP and end-of-life handling.

Materials compatibility is the silent killer. Elastomers (EPDM, FKM), engineering plastics, cable insulation and conformal coatings all live inside the bath for years. Require immersion-ageing data for elastomers per ASTM D471, written compatibility statements for polymers and coatings, and a monitoring plan — colour, acid number, metal content by ICP — with acceptance limits for the pilot loop.

Procurement will also ask about server warranties and industry guidance. Keep the file ready: compatibility statements referenced against OCP immersion-cooling publications and ASHRAE TC 9.9 liquid-cooling guidance, plus the property-set structure used for insulating liquids in IEC 60296 as a benchmark for what a complete fluid datasheet looks like.

What we ship with each batch: certificate of analysis (viscosity, density, moisture, dielectric strength), EU CLP-format SDS, a materials compatibility matrix, and handling guidance for draining, transfer and filtration. The fluid is only half the deliverable; the evidence file is the other half.