Single-Phase Immersion Heat Sinks: Thermal Evaluation and Targeted Flow Technology

Author: Jessica Gullbrand, Mark MacDonald, & Casey Carte, Intel Corporation Collection: 2024 OCP Global Summit - Cooling Environments & Immersion

Summary

Intel's data center group presents two linked innovations for single-phase immersion cooling: a standardized Immersion Flow Tunnel metrology test bed for reproducible heat sink thermal characterization, and Targeted Flow Technology — a method of directing fluid flow directly to CPU heat sinks via a topside manifold rather than relying on bulk tank convection. The problem motivating both is that existing immersion tank designs have unique, non-standardized flow inlet geometries that create different boundary conditions between tanks, making heat sink qualification for one tank invalid for another. The Immersion Flow Tunnel solves the metrology problem; Targeted Flow solves the thermal performance ceiling problem.

Two targeted flow heat sink designs are presented: the Efficiency Heat Sink (thermal resistance ΨCL ≈ 0.055°C/W, contributed to OCP as a public design), which delivers approximately 2x improvement over natural convection with very low pressure drop (<1 kPa at 8 LPM), and the Performance Heat Sink (ΨCL ≈ 0.027°C/W, available under zero-cost Intel license), which delivers approximately 3x improvement over natural convection at the expected operating point of 2 LPM with ~5 kPa pressure drop. Both designs were tested with Airport Cove or Orfs Corner TTV (Thermal Test Vehicles) in PAO 4 fluid at 40°C inlet temperature in Intel's Jones Farm lab in Portland, Oregon.

The Performance Heat Sink enables two transformative capabilities demonstrated at OCP 2024: dual-socket Orfs Corner TTVs running at 1,000W each (in a GRC tank at the Intel booth), and a functional Intel Birch Stream server with Granite Rapids CPUs at 500W TDP in a Submer tank at the Castrol booth. The Birch Stream demo was run at 70°C bath inlet temperature — enabling chiller-free operation and waste heat recovery above 60°C — pointing toward a "High Temperature Immersion" (HTI) pathway for district heating and dry cooling in any climate.