Data center power densities have surged from 4 kW per rack to 12-30 kW and beyond, driven by AI workloads that demand 10× more electricity than traditional searches. Traditional air cooling can no longer handle these thermal loads, making liquid cooling not just preferable but 必要适用于现代 GPU 和 CPU 集群。
为什么液体冷却占主导地位
Liquid coolants carry over 1,000 times more heat than air while reducing energy consumption, water usage, noise, and operating costs. Two primary architectures have emerged: single-phase and two-phase direct-to-chip systems, each with distinct engineering considerations.
单相系统
Single-phase systems circulate water-glycol mixtures or deionized water through cold plates mounted directly on processors. The coolant absorbs sensible heat without changing phase, requiring cooling distribution units (CDUs) and facility water loops with chillers and cooling towers.
Key characteristics:
- Coolant temperature rises as it absorbs heat
- Requires larger volumetric flow rates
- Well-understood infrastructure and maintenance
- Proven track record in hyperscale deployments
两相系统
Two-phase systems leverage latent heat during refrigerant phase change, maintaining uniform chip temperatures through controlled boiling. Liquid refrigerant flows to cold plates where it evaporates, then returns to a condenser as vapor.
Advantages:
- Superior thermal uniformity on chip surfaces
- Reduced system weight and simplified plumbing
- Minimal water consumption (near-zero in many climates)
- Better thermal performance/cost ratio
- Lower pumping power due to efficient heat transfer
制冷剂选择：工程权衡
为两相系统选择制冷剂涉及平衡安全，环境影响和system design要求。
安全等级
A1制冷剂 (non-flammable) avoid restrictions imposed on A2L (mildly flammable) options, simplifying compliance and reducing training requirements. R-1233zd(E) and R-1336mzz(Z) achieve A1 classification with GWP values of 1-2, representing 97-99% reductions versus older refrigerants.
系统设计压力
运营压力直接影响组件成本和可靠性：
| 制冷剂 | 设计压力 | 应用笔记 |
|---|---|---|
| R-513A、R-1234yf | 325-350 磅/平方英寸表压 | 类似于 R-134a 系统 |
| R-1234ze(E), R-515B | 250-275 磅/平方英寸表压 | 适度减压 |
| R-1233zd(E), R-1336mzz(Z) | 70-80 磅/平方英寸 | 压力极低，蒸气量大 |
体积流量注意事项
Low-pressure refrigerants enable smaller liquid-side components but require 3-6× larger vapor return piping compared to R-134a-like options. At 70°F, R-1336mzz(Z) needs 9.86 ft³/min vapor flow per ton versus 1.43 ft³/min for R-134a.
设计寓意：必须权衡较低压力等级带来的成本节约与加大回流歧管和增加压降灵敏度。
监管环境
PFAS 法规将影响两相冷却系统，需要积极主动的制冷剂策略和潜在的运营商认证。工程师在指定系统时应监控 ANSI/ASHRAE 标准 34 更新和 EPA SNAP 批准。
软管、管道和连接设计
组件之间的灵活连接面临着两相系统的严格要求。
材料选择标准
渗透性：汽相制冷剂可以通过软管壁迁移；阻挡层最大限度地减少损失，但降低灵活性。
压力等级：3:1 至 4:1 的设计系数确保爆破压力超过最大工作压力。
流体兼容性：材料必须能够抵抗萃取和降解；聚氯丁二烯、NBR、HNBR、PTFE、聚酰胺和 PPS 已被证明与 R-513A、R-515B 及其成分相容。
方面：内径影响压降和传热；外径决定了密集服务器机架中的空间需求。
橡胶与热塑性塑料
橡胶软管 (EPDM, nitrile, polychloroprene) offers superior flexibility, tight bend radius, and simple barb connections with low assembly force.
热塑性塑料 options (polyamide, PTFE, PFA) provide better chemical resistance, lower permeation, and thinner walls but may require O-ring seals and higher assembly forces.
快速断开接头
QD 干断联轴器可在系统不关闭的情况下实现热插拔服务器。关键绩效指标包括：
- 所需流量下的低压降
- 连接过程中流体损失和空气夹杂最少
- 长度紧凑，机架灵活
- 高真空能力
- 免工具操作
可持续发展影响
Traditional data centers consume billions of liters of water annually with projected double-digit growth. Two-phase systems eliminate most water consumption, offering a clear path to sustainable cooling infrastructure.
实施指南
当指定直接芯片冷却时：
- 将冷却架构与机架密度相匹配： Air cooling remains viable below 12 kW/rack; single-phase for 12-30 kW; two-phase for extreme densities
- 优先使用 A1 级制冷剂简化合规性和运营要求
- 平衡系统压力与组件尺寸– 极低压制冷剂降低了一些成本，但增加了蒸汽管道的复杂性
- 评估材料兼容性贯穿整个流体回路，包括密封件和垫圈
- 适用性设计带有快速断开接头和可触及的歧管
