Views: 0 Author: Site Editor Publish Time: 2026-11-02 Origin: Site
A Coolant Distribution Unit (CDU) is the operational heart of data center liquid cooling systems. It functions as an intelligent thermal transfer and hydraulic isolation bridge between the primary Facility Water System (FWS) and the secondary Technology Cooling System (TCS). Working on a closed-loop thermodynamic cycle, the CDU receives warm dielectric coolant or treated water/glycol (+50∘C to +65∘C) from server cold plates (CPUs, GPUs, and memory modules), passes it through a high-efficiency Brazed Plate Heat Exchanger (BPHE) to transfer thermal energy into the facility water loop (+30∘C to +42∘C) without physical fluid mixing, and utilizes intelligent variable-speed redundant pumps, duplex filtration (50 μm), and expansion/deaeration systems to deliver precisely conditioned, debris-free coolant (+35∘C to +45∘C) back to high-density compute racks at sub-1.02 PUE.
High-performance AI and supercomputing servers cannot circulate raw building chilled water directly across micro-channel cold plates due to the risk of scale, bio-fouling, and catastrophic particulate clogging. A CDU solves this by operating two physically isolated hydraulic circuits:
COMPLETE FLUID & THERMAL FLOW INSIDE A LIQUID COOLING CDU
=================== [1] PRIMARY FACILITY WATER SYSTEM (FWS) ===================
[ Chilled Water / Cooling Tower / Ambient Dry Cooler: Supply +30°C to +40°C ]
│ ▲
Modulating 2-Way Valve Warm FWR Return
│ │
▼ │
┌────────────────────────────────────────────────────────────────────────────┐
│ CSTHEATEXCHANGER® BRAZED PLATE HEAT EXCHANGER (BPHE) CORE │
│ • Counter-current turbulent liquid-to-liquid heat transfer │
│ • 1.5K to 3.5K approach temperature; zero fluid cross-contamination │
└──────────────────────────┬────────────────────────────────┬────────────────┘
│ ▲
Conditioned Coolant: +35°C to +45°C Warm Return: +50°C to +65°C
│ │
▼ │
┌───────────────────────────────────────────────────────────┴────────────────┐
│ [2] SECONDARY TECHNOLOGY COOLING SYSTEM (TCS) CONDITIONING SUITE │
│ ┌────────────────────────┐ ┌────────────────────────┐ ┌──────────────────┐ │
│ │ DUPLEX 50 µm FILTER │ │ N+1 REDUNDANT PUMPS │ │ EXPANSION TANK │ │
│ │ Debris & particle trap │ │ Flow: 50 - 1,200 L/min │ │ & Micro-Deaerator│ │
│ └────────────────────────┘ └────────────────────────┘ └──────────────────┘ │
└──────────────────────────┬─────────────────────────────────────────────────┘
│ ▲
▼ │
==================== [3] SERVER RACK IT COMPUTE HARDWARE ====================
[ High-Density GPU / CPU Micro-Channel Cold Plates & Manifolds (Heat Source) ]Secondary coolant (typically treated deionized water with anti-corrosion inhibitors or low-viscosity propylene glycol, PG25) circulates directly through micro-channel cold plates mounted on high-power processors (GPUs, CPUs, TPUs). The liquid absorbs heat directly from silicon junctions, rising from +35∘C to +65∘C.
The heated secondary coolant leaves the server blade via dripless blind-mate quick disconnects (QD) and enters the CDU manifold return line.
Inside the CDU, the hot secondary coolant flows through alternating stainless steel channels of a vacuum-brazed plate heat exchanger (BPHE). On the opposite channel face, cooler primary facility water (+30∘C to +40∘C) flows in a counter-current direction, absorbing thermal energy across thin corrugated plates without ever mixing fluids.
The primary facility water, now heated, exits the CDU and travels to outdoor ambient dry coolers, evaporative cooling towers, or district heating recovery loops for atmospheric heat dissipation.
The cooled secondary liquid passes through:
Duplex Micron Filters (50 μm to 20 μm): Stripping any microscopic suspended particulates.
Microbubble Deaerator & Expansion Tank: Bleeding out dissolved gas bubbles and buffering thermal volumetric expansion.
N+1 Variable-Speed Redundant Pump Array: Pressurizing the coolant to precise differential pressure setpoints (ΔP=1.5 to 2.8 bar) before routing it back into the server racks.
A high-reliability CDU integrates six mission-critical mechanical and electrical subsystems:
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CSTHEATEXCHANGER CDU INTERNAL SUBSYSTEM MATRIX & FUNCTIONALITY
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Subsystem Component Primary Engineering Function
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1. Brazed Plate Exchanger (BPHE)Provides thermal energy transfer while creating an absolute hydraulic
isolation barrier between primary and secondary fluid loops.
2. Redundant Pump Array (N+1/2N)Maintains continuous coolant circulation across server cold plates with
automatic bumpless failover (< 50 ms) to prevent server throttling.
3. Duplex Precision Filtration Continuous particulate removal (50/20 µm) with online element replacement
capability without requiring system shutdown or fluid bypass.
4. Expansion Tank & Deaerator Absorbs thermal volume expansion as coolant heats up and separates
entrained air/micro-bubbles to eliminate pump cavitation and hotspots.
5. 2-Way Modulating Flow Valve Dynamically throttles primary facility water flow based on server thermal
load to maintain precise secondary supply temperature setpoints.
6. Embedded PLC / Smart TelemetryMonitors pressure, temperature, flow rates, and leak detection cables;
interfaces with DCIM via Redfish, SNMP v3, and Modbus TCP.
================================================================================ CDU DIFFERENTIAL PRESSURE (ΔP) & CONSTANT FLOW REGULATION LOOP
COLD PLATE FLOW DEMAND
HIGH ┤ ▲
│ ╱ ───► CDU Controller Increases Pump RPM
│ ╱
LOW ┤ ──────────────► ─────► CDU Controller Decreases Pump RPM
└────────────────────────────────────────────────────────► SERVER GPU LOAD
RESULT: Constant Differential Pressure Across Every Server BladeAn industrial CDU operates two autonomous closed-loop PID control mechanisms:
The CDU monitors the secondary supply coolant temperature leaving the heat exchanger. If the GPU servers enter an intense AI training phase and coolant temperatures rise:
The internal PLC modulates the primary 2-way motorized control valve, increasing facility water flow across the BPHE.
The heat exchange rate increases instantly, stabilizing the secondary coolant supply at the exact programmed target (e.g., +40∘C±0.5∘C).
GPU cold plates have strict hydraulic resistance profiles. The CDU continuously monitors the pressure differential between the supply manifold and return manifold:
If server blades are dynamically hot-swapped or variable valves adjust, the CDU automatically ramps pump variable frequency drives (VFD) up or down to maintain a constant ΔP, preventing pump cavitation or insufficient flow to critical processors.
Different data center layouts require tailored CDU form factors depending on density and scalability:
COMPARISON OF CDU ARCHITECTURAL CONFIGURATIONS
[1. IN-RACK CDUs (40 kW - 120 kW)]
• Form Factor: 4U to 8U EIA-310 19"/21" rack-mount chassis.
• Scope: Dedicated to a single high-density AI server rack.
• Best For: Modular edge data centers and isolated high-power GPU clusters.
─────────────────────────────────────────────────────────────────────────────
[2. IN-ROW CDUs (200 kW - 600 kW)]
• Form Factor: Standard 300 mm or 600 mm wide server cabinet footprint.
• Scope: Distributes secondary coolant to an entire row of 4 to 8 racks.
• Best For: Enterprise AI clusters and medium-scale hyperscale pods.
─────────────────────────────────────────────────────────────────────────────
[3. CENTRAL / FLOOR-STANDING CDUs (800 kW - 2.5 MW+)]
• Form Factor: Heavy-duty floor-mounted mechanical skid.
• Scope: Centralized liquid distribution feeding hundreds of server cabinets.
• Best For: Hyperscale AI data halls and supercomputer installations.(Note: The following engineering parameters represent standard manufacturing design envelopes. Custom flow rates, heat capacities, redundant pump architectures, and communication protocols are engineered to order.)
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CSTHEATEXCHANGER COOLANT DISTRIBUTION UNIT (CST-CDU SERIES)
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Engineering Parameter Standard Manufacturing & Design Range
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Thermal Cooling Capacity Range 50 kW (In-Rack) to 2,500+ kW (Central Floor Skids)
Hydraulic Decoupling Mechanism Vacuum-Brazed Plate Heat Exchanger (SS316L / Titanium)
Approach Temperature (FWS/TCS) 1.5K to 3.5K (Enables 100% Free Cooling Operation)
Secondary Coolant Flow Capacity 50 to 2,000+ L/min (13 to 530+ GPM) Modulated
Secondary Loop Pressure Head 1.5 to 3.5 bar (21.7 to 50.8 psi) Variable Differential
Pump Redundancy Architecture N+1 Active/Standby or 2N Dual Mag-Drive / Canned Motors
Switchover Failover Latency < 50 ms Bumpless Dynamic Transfer (Zero Pressure Dip)
Filtration System Standard Duplex 50 µm / 20 µm Stainless Steel Basket Filters
Expansion Vessel & Deaerator Integrated Stainless Steel Sealed Tank with Auto-Bleeder
Primary Facility Water Temp +20°C to +45°C (Compatible with ASHRAE W1 - W5 Classes)
Secondary Technology Supply +25°C to +50°C (Optimized for Direct-to-Chip Cold Plates)
Instrumentation & Sensors Turbine/Electromagnetic Flow Meters, RTDs, Pressure Transducers
Leak Detection & Safety System Optical Liquid Sensors, Perimeter Sensing Rope, Auto-Shutoff
Automation & Telemetry Redfish API, SNMP v3, Modbus TCP/RTU, BACnet IP, Dual GbE LAN
Quality, Safety & Electrical UL 62368-1, CE / PED, ASME Sec. VIII, ISO 9001:2015
================================================================================Facility water systems contain dissolved minerals, rust particles, biological algae, and erratic pressure fluctuations. Circulating facility water directly through server cold plates would rapidly clog micro-channels (<0.1 mm fins), cause galvanic corrosion, and create catastrophic server rack flooding risks during maintenance. The CDU provides an essential hydraulic and chemical firewall.
Because CSTHEATEXCHANGER CDUs utilize high-efficiency Brazed Plate Heat Exchangers with an ultra-tight approach temperature (1.5K to 3.5K), secondary coolant can operate at +40∘C to +45∘C with primary water at +35∘C to +40∘C. This allows ambient outdoor dry coolers to dissipate 100%100% of the heat load without mechanical chillers, drastically slashing data center PUE to <1.02.
In an N+1 redundant CDU, the standby pump is continuously primed with dual check valves. When internal pressure or RPM sensors detect a primary pump anomaly, the controller engages the standby pump in <50 ms. The check valve prevents backflow, maintaining steady flow and pressure to the GPUs with zero server downtime.
Ensure uninterrupted computing velocity and maximum thermal efficiency for your AI data center with CSTHEATEXCHANGER:
High-Density In-Rack (50 kW–120 kW), In-Row (200 kW–600 kW), and Central (1.5 MW+) CDUs
Custom Brazed Plate Heat Exchangers (AISI 316L / Titanium / Nickel Brazing)
N+1 / 2N Redundant Canned-Motor Pumps with <50 ms Bumpless Failover
Integrated Duplex Filtration (50 μm), Expansion Chamber, and Micro-Bubble Deaeration
Full Redfish API, SNMP v3, and Modbus TCP Data Center Infrastructure Integration
Direct Engineering Support, CFD Simulation, 3D CAD Modeling & Global Factory Supply
Contact our specialized liquid cooling thermal engineering team today with your server rack power density, target supply temperatures, flow requirements, and enclosure envelope for customized proposals and factory-direct quotations.
Website: https://www.cstheatexchanger.com/
Technical Inquiries: info@cstheatexchanger.com
