Liquid Cooling Components for AI Servers: Cold Plates, Manifolds, QDs and CDUs

Quick answer: An AI server liquid-cooling loop is not one component. The cold plate collects heat at the processor, hoses and quick disconnects connect serviceable hardware, a rack manifold distributes supply and return flow, and the coolant distribution unit (CDU) circulates and conditions the technology-side coolant while transferring heat toward the facility system.

For sourcing teams, the practical risk is at the interfaces. A well-machined cold plate can still fail the project if port orientation, seal geometry, coolant compatibility, cleanliness, mounting flatness or test responsibility is unclear.

The Direct-to-Chip Cooling Path at a Glance

The Open Compute Project cold-plate requirements describe a rack manifold as the component that distributes cooling liquid from the CDU to IT equipment and back. They also describe quick disconnects as serviceable couplings that shut off flow when disconnected. These definitions are useful because they separate component roles before drawings and supplier scopes are discussed.

Cold Plates: The Device-Level Heat Interface

A cold plate normally combines a thermal contact surface with an internal wetted path. Heat crosses the interface from the processor package into the plate, then into coolant moving through channels or enhanced internal features. The plate may also contain sealing grooves, cover interfaces, fittings, mounting holes and local reliefs.

The thermal engineer owns the required heat load, flow conditions and allowable pressure drop. The manufacturer needs a drawing that converts those requirements into inspectable geometry. Critical items usually include the contact area, flatness or profile requirement, surface-finish callout, channel geometry, minimum walls, port details, seal specification and the condition in which dimensions are inspected.

Fengnuo's relevant scope is drawing-based CNC machining of component bodies and interfaces. This does not mean Fengnuo supplies a complete rack cooling system or accepts responsibility for system-level thermal performance.

Rack Manifolds: Distribution Depends on More Than Port Count

A rack manifold provides supply and return paths to multiple server nodes. Its appearance may be simple—a tube, rail or machined block—but the design has to manage port spacing, connection access, internal transitions, pressure drop and flow distribution across branches.

For a machined manifold block, a supplier should review drill access, intersecting passages, cross-hole closures, thread standards, sealing faces, burr removal and cleaning. If angled ports or multi-face passages create difficult access, 5-axis machining may reduce setups, but it should be selected from the geometry rather than treated as an automatic requirement.

Quick Disconnects and Hoses Are System Interfaces

Quick disconnects make server service possible without draining the entire loop. Their nominal size alone is not enough. The specification needs the mating series, hand-mate or blind-mate arrangement, seal material, coolant compatibility, allowable connection force, installation envelope and intended flow direction.

Hose and tube routing also affects assembly. A connector placed correctly in CAD may still be difficult to grip, torque or release inside a crowded server tray. The RFQ should include the surrounding keep-out volume and the expected assembly sequence, not only the isolated part model.

What the CDU Does—and What It Does Not Tell the Part Supplier

ASHRAE describes a common arrangement in which the CDU separates the facility water system from the technology cooling system through a heat exchanger. The CDU may circulate coolant, transfer heat, control temperature and pressure, filter the loop and monitor operating conditions.

However, a CDU selection does not automatically define a cold plate or manifold drawing. The component supplier still needs the actual coolant, operating and test conditions that apply at the part. Flow ranges, pressure limits and temperatures must come from the system owner; they should not be guessed from a generic server-cooling diagram.

The Manufacturing Boundary Buyers Should Define

Before requesting quotations, divide the project into design ownership, manufacturing scope and validation scope. This prevents a machining supplier from being judged against an unstated thermal target or a system integrator from assuming that every component manufacturer performs the same joining and testing operations.

• System design: heat load, coolant chemistry, flow distribution, redundancy and facility integration.
• Component design: interfaces, materials, seals, channels, ports, mounting and acceptance criteria.
• Manufacturing: stock preparation, machining, deburring, cleaning, joining or coordinated secondary operations.
• Verification: dimensional inspection, cleanliness, leak or pressure test method, flow test and documentation—only where specified.

RFQ Checklist for Liquid-Cooling Components

• 3D CAD and revision-controlled 2D drawings.
• Component role: cold plate body, cover, manifold, bracket, fitting interface or assembly.
• Material grade for every wetted and non-wetted component.
• Coolant name, concentration, temperature range and compatibility restrictions.
• Supply and return port standards, thread or fitting details, and keep-out zones.
• Critical contact surfaces, datum structure, flatness, roughness and mounting requirements.
• Joining and sealing ownership, including seal material and groove standard where applicable.
• Leak, pressure, flow, cleanliness and documentation requirements, with test conditions.
• Prototype quantity, expected production quantity and change-control expectations.

Frequently Asked Questions

Is a cold plate the same as a CDU?

No. A cold plate is the device-level heat-transfer component. A CDU circulates and conditions the technology-side coolant and exchanges heat with the facility side.

Does every cold plate use the same coolant?

No. Coolant chemistry and material compatibility are system decisions. The drawing and RFQ should name the fluid and operating conditions instead of assuming that water, glycol mixtures or dielectric fluids are interchangeable.

Can a CNC supplier guarantee server cooling performance?

Only when responsibilities, test conditions and acceptance criteria are explicitly defined. Machining can control specified geometry and interfaces; overall thermal performance also depends on heat load, TIM, mounting, coolant, flow and the rest of the loop.