Inside CDU Liquid Cooling Core Modules Unveiled
Many operators regard CDU merely as a simple heat exchange cabinet without understanding its internal components and respective functions. This article disassembles a complete CDU unit and elaborates on six core functional modules with detailed design rationale, supporting stable operation of CDU liquid cooling systems.
Short for Cooling Distribution Unit, a CDU undertakes three core tasks in liquid cooling loops: cold energy transfer, circuit isolation and even flow allocation. It shifts cooling capacity from primary water to secondary server cooling loops, physically separates two circuits with different water quality and pressure standards, and distributes chilled fluid evenly to cabinet cold plate branches. One CDU typically serves 8 to 20 racks under row level liquid cooling layouts, with power specifications ranging from 30kW to 200kW to match diverse computing loads.
Plate heat exchanger acts as the core component isolating primary and secondary circuits, stacked with dozens of corrugated plates for high-efficiency heat exchange above 93%. Made of 316L stainless steel or titanium, it forms the foundation of mature cold plate liquid cooling. Operators need regular endoscopic inspections to avoid scale buildup that reduces heat transfer efficiency and threatens high-power GPU hardware.
Circulation pumps provide power for closed secondary loops, adopting 1+1 or 2+1 redundant setup with automatic switchover within 5 seconds to prevent GPU overheating and throttling. Variable frequency pumps cut energy consumption and deliver precise flow control, which is critical for stable operation of high-load GPU server liquid cooling. Staff must conduct particle detection after pump switching to avoid pipeline sediment blockage.
Electric regulating valves serve as temperature control actuators, adjusting primary water flow based on real-time secondary supply temperature with ±0.5°C accuracy. Most data centers select fail-open valves to guarantee continuous cooling for liquid cooled server clusters during power outages, while teams need to monitor dew point risks to avoid internal condensation damage.
Expansion tanks buffer volume and pressure fluctuations of coolant, equipped with nitrogen-filled rubber diaphragms to absorb thermal expansion of liquid. Proper pre-charged nitrogen pressure and 5%-10% system volume capacity effectively stop pipeline leakage and overpressure, a necessary configuration for complete data center liquid cooling solution.
Multi-stage filters protect delicate cold plate microchannels by intercepting solid particles via 50μm coarse filters and 20μm fine filters. Differential pressure gauges indicate clogging status, and standardized cleaning procedures prevent filter deformation, greatly lowering failure risks for large-scale AI data center cooling deployments.
The control unit works as CDU’s central nervous system, integrating PLC and full sets of temperature, pressure, flow and leakage sensors. Supporting Modbus and BACnet communication protocols, it connects with DCIM platforms for remote monitoring and automatic fault alarms, applicable to both fixed rack clusters and modular container data center liquid cooling scenarios.
An optional automatic liquid replenishment system compensates for long-term coolant loss via storage tanks and liquid level sensors, avoiding pump air suction caused by insufficient fluid volume. Strict sanitation management during replenishment prevents foreign particles from entering the whole liquid cooling circulation.
The integrated fluid circulation path links all six modules into a closed loop. Primary water flows through regulating valves and releases heat inside plate heat exchangers, while secondary coolant absorbs cold, circulates through server cold plates and returns via filters. Equipped with pressure buffer expansion tanks and intelligent control units, the whole CDU framework delivers reliable, standardized cooling support for all high-density computing infrastructure.
Globally recognized for liquid cooling expertise, EXTRCOOL engineers custom solutions for high-density AI and HPC data centers. Our premium thermal lineup—dual-mode CDUs, manifolds, cold plates, rear-door heat exchangers, dry coolers, and containerized units—delivers consistent reliability, smooth integration, and straightforward scalability for a turnkey one-stop full liquid cooling deployment. We collaborate with data center operators and enterprises across North America, East Africa, Western Europe, East Asia, and Australia.
