Introduction to Single-Phase vs. Two-Phase Immersion Cooling
Immersion cooling technology involves submerging servers in a dielectric fluid, leveraging the liquid’s high thermal conductivity to surpass the heat dissipation limits of traditional air cooling. To keep pace with the future trend of high-density and high-power AI servers, developments have moved beyond just single-phase immersion cooling systems.
Single-Phase - Immersion Cooling System
只利用液體的液態單相，就像大型封閉式水冷一樣，透過強制對流來散熱，因此鰭片是關鍵設計，用以擴大散熱面積與優化流道。
這類系統建議使用與散熱器及晶片相容的熱介面材料，以確保可靠的熱傳導。
Two-Phase - Immersion Cooling System
兩相系統主要利用核沸騰的原理來帶走熱量，其熱傳導效率極高。研究顯示，在這種情況下，過多的鰭片反而可能阻礙氣泡的生成與脫離，降低效率。
因此，許多兩相設計會使用裸露或經過微結構處理的平面，以最佳化沸騰與氣泡排散。
單相液冷系統&兩相液冷系統動畫說明
Single-Phase
Temperature
65°C
PUE
1.05-1.12
Flow Rate
2-5 L/min
Heat Exchanger
DTT61-s
- High Boiling Point Dielectric Fluid
- Pump-Driven Circulation
- Forced Convection Heat Transfer
- System is Simple and Easy to Maintain
Two-Phase
Boiling Temperature
55°C
PUE
1.01-1.03
Pressure
密封系統
Copper Coil Condenser
- Low Boiling Point Dielectric Fluid
- Natural Circulation
- Nucleate Boiling Phase Change
- Extremely High Heat Flux
Cooling Principle
Air Cooling
Air
Single-Phase
Liquid
Two-Phase
Latent Heat
Drive Method
Air Cooling
Fan
Single-Phase
Pump
Two-Phase
Convection
Cooling Efficiency
Air Cooling
Normal
Single-Phase
Good
Two-Phase
Excellent
Setup Cost
Air Cooling
Normal
Single-Phase
Normal
Two-Phase
Extremely
A Comparison of Two-Phase and Single-Phase Liquid Cooling Systems
|
Two-Phase
|
Single-Phase
|
|
|
Heat transfer performance
|
Local convective heat transfer coefficient can reach thousands of W/m²·K; phase change enables very high heat flux and temperature stability.
|
Convective coefficient is only tens of W/m²·K; requires fins to increase area and optimized thermal interface materials to reduce interfacial resistance.
|
|
Energy efficiency
|
Maximizes energy efficiency.
|
Significantly better than air cooling; balances performance and cost.
|
|
Mechanism
|
Low-boiling dielectric fluid nucleate-boils at hotspots, carrying away latent heat; vapor condenses back to liquid. Heat transfer relies on phase change.
|
High-boiling dielectric fluid directly contacts the heat source and rejects heat via a heat exchanger without phase change, relying on natural or forced convection.
|
|
System complexity
|
High: requires sealed tanks, boiling and condensation management, and gas–liquid separation; higher design and build CAPEX.
|
Low: open or simple circulation systems; no phase-change management; simpler installation and maintenance.
|
|
Fluid cost and environment
|
Fluids are often fluorinated compounds with high cost and GWP/PFAS risks, creating strong regulatory pressure.
|
Fluid formulations can be customized, emphasizing long service life and corrosion inhibition, with lower environmental risk.
|
|
Use cases
|
Extreme heat density, space-constrained, high-performance computing facilities with boiling management and sealing capability. |
Large-scale cloud and enterprise deployments, edge computing, where high availability and low maintenance are required.
|
|
Maintenance requirements
|
Strict: prevent fluid evaporation, perform regular leak checks, and clean condensers. |
Lower: long fluid life with no phase-change degradation; maintenance similar to conventional liquid cooling.
|
Thermal Pads for Single-Phase Immersion Cooling
DTT61-s
6.0 W/m·K
Single-Phase Immersion Cooling
