A Novel Functional Accelerated Thermal Aging Methodology for Single-Phase Dielectric Immersion Coolants

High-performance computing is significantly transforming the thermal management landscape in data centers. Immersion cooling presents a promising solution to efficiently cool high-density server racks while drastically lowering the energy footprint of this industry. Coolant research is key in the global deployment of immersion cooling systems, although these studies remain rather scarce. From an operational perspective, the coolant quality over time and corresponding lifespan are key concerns. However, little is known about how these parameters behave under actual server operating conditions. Therefore, this work introduces a comprehensive aging methodology to evaluate the quality of dielectric immersion coolants over time and predict their lifespan in single-phase immersion cooling applications. The approach involves the accelerated thermal aging of a dielectric immersion coolant at 100 °C for six months. Subsequently, the thermo-electrical performance of the aged coolant is validated using an immersed Raspberry Pi 4 Computer. A biobased synthetic ester dielectric coolant (L759, Oleon NV) was selected because such chemistry can effectively balance crucial performance and safety metrics. Its low viscosity supports efficient heat transfer, as demonstrated by the high Mouromtseff number and thermal figures of merit 1-3, all of which exceeded established threshold values. Also, L759 exhibited a high flash point, high electrical resistivity, and high dielectric breakdown, conforming to fire and electrical safety guidelines. Furthermore, the coolant showed minimal interactions with polyvinyl chloride, a widely used cable insulation material. Additionally, the product is safe to handle and has an excellent environmental profile. Due to the careful selection of use case materials, the proposed system-oriented aging methodology successfully simulated actual material-liquid interactions. Thermal aging and use case data further identified the acid value (physical; primary), specific heat capacity (thermal; secondary), and electrical resistivity (electrical; secondary) as crucial coolant lifespan indicators. Furthermore, the aged coolant properly cooled the central processing unit on the Raspberry Pi 4 Computer, as reflected in thermo-physical and dielectric/electrical property data. No material incompatibilities were observed during functional testing. Overall, L759 can comply with the lifespan of current (five years) and next-generation (seven, up to 10 years) servers. Hence, ester technology shows great potential in operating single-phase immersion cooling systems. The presented methodology integrated material compatibility, thermal stress, and functional performance factors. It can easily be extrapolated to alternative coolant chemistries and even to adjacent application domains, thereby contributing to standardization efforts across the broader industry.