iDLC Implications on Balance of Immersion Cooling System
Author: John Bean, Green Revolution Cooling (GRC); OCP Immersion Project Co-Lead Collection: 2024 OCP Global Summit - Cooling Environments & Immersion
Summary
John Bean (co-lead of the OCP Immersion project and Principal at GRC — Green Revolution Cooling) presents a systems-level analysis of how iDLC (immersion Direct Liquid Cooling) — specifically the addition of targeted/directed flow heat sinks to immersion tanks — increases total dielectric fluid flow rates through the CDU (Coolant Distribution Unit), and how intelligent heat exchanger bypass valve strategies can recover pumping efficiency without sacrificing thermal performance.
The core problem: in a standard immersion tank, the fluid simply circulates through the tank and CDU. When directed flow heat sinks are added (each requiring ~2.5 LPM), a 50U rack with 200 heat sinks requires 500 LPM for heat sinks alone, plus ~200 LPM for bulk tank circulation — totaling 700 LPM that all flows through every CDU element including the heat exchanger, which represents the largest single pressure drop in the system. The proposed solution is a motorized bypass valve around the heat exchanger that diverts a fraction of the dielectric flow around the heat exchanger (not cooling it), then remixes it with the cooled fraction. This reduces pressure drop and pump power, but requires dynamic optimization to find the sweet spot before increased water-side pumping power cancels the dielectric-side savings.
The analysis, conducted using an Alfa Laval heat exchanger performance prediction tool (not product-specific), shows heat exchanger fluid power savings of 11–34% depending on operating scenario, with the most favorable scenario cutting HX (heat exchanger) fluid power from 982W to 647W — a ~34% reduction — under a specific load and bypass configuration. The study covers three scenarios: 250 kW at 100% load (2.5 LPM/heat sink), 200 kW at 80% load (2.0 LPM/heat sink), and 250 kW at 100% load (4.0 LPM/heat sink — performance heat sink).
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