Abstract:

As server power consumption continues to rise, traditional air cooling technology is becoming increasingly limited due to drawbacks such as high energy consumption, high noise, and insufficient cooling capacity. Single-phase immersion cooling has consequently emerged as a focal point of research, owing to its superior heat-transfer coefficient, markedly lower energy requirement, and negligible noise generation. First, the physical properties of three typical single-phase immersion coolants—mineral oil, silicone oil, and fluorocarbon fluid—were compared and analyzed. The results show that the density of oil-based coolants (mineral oil and silicone oil) is approximately half that of fluorocarbon fluid, and their specific heat capacity and thermal conductivity are nearly twice that of fluorocarbon fluid. However, their viscosity is one to two orders of magnitude higher, resulting in a significant increase in boundary layer thickness. Second, computational fluid dynamics (CFD) simulations were performed on a canonical server configuration to quantify the cooling efficacy of each fluid, and a novel heat dissipation coefficient (HDC) was introduced as a comprehensive performance metric. The HDC analysis reveals that the SS-110 coolant delivers exceptional flow-boiling performance, a benefit primarily attributable to its ultra-low kinematic viscosity. Finally, a dedicated single-phase immersion cooling testbed was designed and commissioned to experimentally validate the thermal performance of mineral oil. At a volumetric flow rate of 1080 L/h, the system successfully removed 1600 W of heat; nevertheless, a non-uniform flow distribution produced a maximum temperature difference of 9.8℃ among heated patches mounted on different epoxy substrates. Additionally, it was observed that thermal grease partially dissolves when exposed to silicone oil, rendering it unsuitable for immersion systems employing silicone oil as the working fluid.

Key words: single-phase immersion cooling, coolant, computational fluid dynamics, flow and heat transfer, heat dissipation coefficient

摘要：

随着服务器功耗持续攀升，传统风冷技术因能耗高、噪声大及冷却能力不足等缺陷逐渐受限。单相浸没液冷技术凭借传热系数大、能耗低、噪声低等优势成为研究热点。首先，针对矿物油、硅油和氟碳液三种典型单相浸没冷却液的物性进行对比分析。结果显示，油基冷却液（矿物油与硅油）的密度约为氟碳液的1/2，比热容和热导率接近氟碳液的2倍，但黏度却高出氟碳液1~2个数量级，导致边界层厚度显著增加。其次，以典型服务器为研究对象，采用计算流体力学（CFD）方法模拟不同冷却液的冷却效果，并提出析热系数（HDC）作为性能评价指标。HDC分析表明，SS-110冷却液具有优异的流动换热特性，其核心优势在于极低的运动黏度。最后，设计并搭建单相浸没液冷实验系统，对矿物油的冷却效果进行实测。实验结果显示，在矿物油流量为1080 L/h时，可以带走1600 W的热量，但是存在流量分配不均匀现象，导致不同环氧树脂板上的发热片平均温度相差可达到9.8℃。此外，实验发现导热硅脂在硅油环境中出现部分溶解现象，因此，不建议将导热硅脂应用于以硅油为冷却介质的浸没液冷系统。

关键词: 单相浸没液冷, 冷却液, 计算流体力学, 流动传热, 析热系数