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
Utilizing only the single-phase liquid state, similar to large-scale closed-loop liquid cooling, heat is dissipated via forced convection. Fins serve as the key design feature to maximize heat dissipation area and optimize flow channels. Thermal interface materials compatible with both the heat sink and chip are recommended to ensure reliable thermal conductivity.
Thermal interface materials compatible with both the heat sink and chip are recommended to ensure reliable thermal conduction.
Two-Phase - Immersion Cooling System
Here is the translation: Two-phase systems primarily utilize the principle of nucleate boiling to dissipate heat, achieving exceptionally high thermal transfer efficiency. Research indicates that in this context, an excessive number of fins may actually impede bubble nucleation and departure, reducing overall efficiency.
Therefore, many two-phase designs employ bare or micro-structured surfaces to optimize boiling performance and bubble departure.
Single-Phase & Two-Phase Liquid Cooling Systems
Single-Phase
- High Boiling Point Dielectric Fluid
- Pump-Driven Circulation
- Forced Convection Heat Transfer
- System is Simple and Easy to Maintain
Two-Phase
- Low Boiling Point Dielectric Fluid
- Natural Circulation
- Nucleate Boiling Phase Change
- Extremely High Heat Flux
Cooling Principle
Drive Method
Cooling Efficiency
Setup Cost
A Comparison of Two-Phase and Single-Phase Liquid Cooling Systems
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Two-Phase
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Single-Phase
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Heat transfer performance
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Local convective heat transfer coefficient can reach thousands of W/m²·K; phase change enables very high heat flux and temperature stability.
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Convective coefficient is only tens of W/m²·K; requires fins to increase area and optimized thermal interface materials to reduce interfacial resistance.
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Energy efficiency
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Maximizes energy efficiency.
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Significantly better than air cooling; balances performance and cost.
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Mechanism
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Low-boiling dielectric fluid nucleate-boils at hotspots, carrying away latent heat; vapor condenses back to liquid. Heat transfer relies on phase change.
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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.
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System complexity
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High: requires sealed tanks, boiling and condensation management, and gas–liquid separation; higher design and build CAPEX.
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Low: open or simple circulation systems; no phase-change management; simpler installation and maintenance.
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Fluid cost and environment
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Fluids are often fluorinated compounds with high cost and GWP/PFAS risks, creating strong regulatory pressure.
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Fluid formulations can be customized, emphasizing long service life and corrosion inhibition, with lower environmental risk.
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Use cases
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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.
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Maintenance requirements
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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.
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Thermal Pads for Single-Phase Immersion Cooling
