Pumping Innovation - Long-term Testing with an Immersion Cooling Fluid

Author: Yann Passard, Group Director Business Support & Application Solutions Europe, Wilo SE; Sandra Duncker, Senior Technologist, Castrol Germany GmbH Collection: 2025-OCP-EMEA-Summit-Immersion-Cooling

Summary

This session presents the results of a two-year cross-company collaboration between Wilo SE (pump manufacturer) and Castrol (lubricants/fluids) to develop and validate a pump-fluid compatibility testing methodology for immersion cooling applications. Presented at the 2025 OCP EMEA Summit in Dublin, the study addresses a critical gap: pumps operating 24/7 in immersion cooling tanks are a key reliability component, yet no defined rules exist for fluid/pump combination testing, and OCP's material compatibility guidelines were designed for static conditions rather than dynamic (moving-part) applications.

The study used Castrol ON — a synthetic hydrocarbon-based oil with an additive package — tested against a Wilo high-efficiency pump in an accelerated aging protocol at 80°C (significantly above typical operating temperatures, deliberately chosen to stress both pump and fluid). The test protocol ran 1,500 hours in cycling mode (7h55m ON / 5min OFF), with continuous monitoring of flow, power, and temperature. Fluid volume in the test bench was 80 liters with flow rate of 1,500 L/h at 1.2 bar static pressure.

The first test trial revealed a critical issue: the pump's polypropylene (PP) impeller showed abnormal behavior after 1,000 hours of exposure to the thermal management fluid. Tensile strength testing showed the new impeller had a max force of 409 N; after 500h aging the value dropped to 229/185 N (known behavior, not critical); after 1,000h aging it dropped to 135/164 N (abnormal behavior). The problem would not have been detected using existing OCP static compatibility guidelines. A second trial with PPS (polyphenylene sulfide) impeller material resolved the issue, and the pump performed without degradation over the full test duration. Fluid analysis confirmed Castrol ON remained fully within OCP Immersion Requirements specification after 1,500 hours of accelerated aging.