Flow Rate and inlet temperature considerations for direct immersion of a single server in mineral oil

Complete immersion of servers in electrically nonconductive mineral oil has recently become a promising technique for minimizing cooling energy consumption in data centers. Liquid cooling in general offers significant advantages over traditional air cooling approaches due to the higher heat capacities of fluids. However, a lack of sufficient published data and long term reliability documentation of oil immersion cooling makes most data center operators hesitant to apply these approaches to their mission critical facilities. In this study, a single server was fully submerged horizontally in mineral oil. Experiments were conducted to observe the effects of varying the volumetric flow rate and oil inlet temperature on thermal performance and power consumption of the server. Specifically, temperature measurements of the CPUs, motherboard components, and bulk fluid were recorded at steady state conditions. Comparing with results from baseline tests performed with traditional air cooling show promise for mineral oil as a viable cooling alternative for data centers. Overall, the cooling loop was able to achieve partial power usage effectiveness (pPUE_Cooling) values as low as 1.03. This server level study provides a preview of possible facility energy savings by utilizing high temperature, low flow rate oil for cooling. A discussion on additional opportunities for optimization of IT hardware and implementation of oil cooling is also included.