Learn How Quick Disconnect Connectors Ensure Reliable Liquid Cooling Systems in AI Datacenters

The deployment of artificial intelligence (AI) is increasing the demand for high-performance datacenters and advanced computing infrastructure. These systems generate significant heat, and designers are finding traditional convection and forced-air cooling increasingly inadequate to meet their thermal management requirements. For next-generation computing centers, designers are turning to liquid cooling for its highly efficient heat dissipation. The challenge for designers is that computing systems need to be scaled, modified, maintained, and replaced without dismantling the cooling system.

Part of the solution lies in liquid cooling connectors that can be quickly connected or disconnected, enabling efficient cooling without sacrificing maintenance flexibility or modular expandability. Such connectors need to be compact, reliable, corrosion resistant, leak-free, and easy to use, with high mating-cycle durability.

This article provides a brief overview of the challenges designers of AI infrastructure cooling systems face. It then introduces quick-disconnect (QD) liquid cooling connectors from Amphenol and shows how to select and apply them to address these challenges.

Quick disconnects

Liquid cooling for electronics, at its most basic, uses a coolant circulating under pressure to cool electronic devices mounted on cold plates and connected to external heat exchangers. The heated coolant exits the cold plate and is circulated to the heat exchanger, where it is cooled and then recirculated. When multiple devices need to be cooled, manifolds distribute coolant to each cold plate. Common coolants include deionized water, ethylene glycol, and propylene glycol. These coolants are nonconductive, preventing damage to powered electronics in the case of a leak. Each heat exchanger needs both an input cold line and an output hot line.

The tricky part is designing the system so the cold plate and electronic device can be removed without disassembling the cooling system. This is where QD connectors come in (Figure 1). These universal QD (UQD) plug and blind mount (UQDB) socket devices allow coolant lines to be separated without leaking.

Figure 1: Shown are examples of a liquid cooling UQD plug and UQDB socket illustrating their mating action. (Image source: Amphenol)

Available in multiple sizes, terminations, and connection configurations, these connectors help designers integrate coolant connections across a wide range of industrial and datacenter architectures. The UQDB sockets are designed to blind mate with the UQD plug in enclosed racks without access to the back of the cabinet. The plug and socket are each mounted on their respective cold plate at defined locations using threaded studs. O-rings seal the QD body to the mounting surface. Each cold plate has two QD connectors: one for the cold coolant and one for the heated return coolant. When the server or other electronic device is installed, the socket, with its conical opening, guides the plug into the mated configuration. The QD connectors are generally marked with identification rings: blue for cold lines, and red for warm returns.

These QD connectors feature a dry disconnect operation that seals against coolant leaks when uncoupled. They contain internal valves that remain closed during coupling until the mating halves are fully engaged, then open for maximum coolant flow. When uncoupled, the valves close before the seal is broken, sealing the coolant channel and preventing leakage.

Open Compute Project

The Open Compute Project (OCP) is an organization that applies the benefits of open source and open collaboration to hardware development, accelerating innovation in the computer industry. Cooling systems are one of their areas of concern. They have released UQD and UQDB specifications, which describe the characteristics of these connectors.

The OCP specifies QD devices in four sizes: UQD02, UQD04, UQD06, and UQD08 (and UQDB02, UQDB04, UQDB06, and UQDB08). The number in the designation indicates the fluid opening diameter and corresponds to 1/8", 1/4", 3/8", and 1/2", respectively. The fluid opening determines the connector's maximum flow rate.

Single source for QD connectors

For designers of liquid cooling systems, it is efficient to have a reliable single source of QD connectors.

Amphenol has introduced a series of UQD/UQDB pairs in a wide range of OCP sizes, mounting options, and terminations. They are engineered for rugged environments common in datacenter applications. The shell material for all components in this family is stainless steel. The internal components exposed to the coolant, such as internal springs, are made of corrosion-resistant stainless steel. They are designed to work with widely used coolants, and all components in the series are rated to working pressures of 0 to 87 pounds per square inch (PSI) (0 to 0.6 megapascals (MPa)). They can sustain a maximum safe pressure of 290 PSI (2.0 MPa) and operate over a temperature range of -40°C to +105°C.

For example, the UQDBP-02TMU01-N000 (Figure 2) is an OCP-compliant (revision 1.0) UQDB02 plug with an external UNF 7/16-20 threaded stud for termination, and uses O-ring seals.

Figure 2: The UQDBP-02TMU01-N000 is an OCP-compliant UQDB02 plug with an external threaded stud for termination. (Image source: Amphenol)

Pressure in a liquid cooling system is analogous to voltage in an electrical circuit. Flow rate is the equivalent of current. The flow rate is described by the flow coefficient (Cv); the higher the Cv, the greater the flow capacity. The Amphenol UQDB02/04/06/08 disconnects have Cv values of 0.4, 1.32, 2.11, and 3.83, respectively.

A flow-rate curve plots pressure across the disconnect as a function of the flow rate (Figure 3).

Figure 3: A typical flow-rate plot shows the relationship between flow rate and pressure difference across the disconnect for the four connector sizes UQDB02 through UQDB08. (Image source: Amphenol)

Given that the flow rate increases proportionally with the connector diameter, the required flow rate determines the device selected. Note that the pressure across the disconnect increases with an increasing flow rate.

Of concern in electronic applications is minimizing the presence of liquids in the environment. With this in mind, the QDs also specify fluid loss upon disconnecting. The Amphenol UQDB02/04/06/08 connectors have fluid loss specifications of 0.004, 0.004, 0.006, and 0.01 milliliters (ml), respectively.

The other half of the QD connector pair is the UQDBS-02TMU02-N000 (Figure 4) blind mate socket with a UNF 9/16“-18 thread.

Figure 4: The UQDBS-02TMU02-N000 is a blind mate socket with a UNF 9/16”-18 thread. (Image source: Amphenol)

The UQD/UQDB series employs a push-to-connect latching mechanism that ensures secure, leak-resistant connections between cooling system elements. The UQDB02 plug mates with this socket with a mating force of 49 newtons (N) (10.6 pounds force) at zero pressure. The mating force increases with increasing connector diameter (58 N, 60 N, and 68 N for UQDB04/06/08, respectively).

Another alternative termination is a hose barb for coupling a hose to the socket, as used in the UQDS-02HSH01-L000 (Figure 5).

Figure 5: The UQDS-02HSH01-L000 is an example of a UQD02 socket with a hose barb termination and blue identification rings indicating it carries cold coolant. (Image source: Amphenol)

A hose allows greater flexibility in connecting the elements of a cooling system. The hose barb accepts a hose with an internal diameter (ID) of 1/4 inch (in.). Larger connector sizes in the series pair with larger hose barbs to maintain appropriate flow rates.

The identification bands, as mentioned earlier, mark the connector as carrying cold or hot coolant.

The sockets are also available with a release button, as in the UQDLS-02HSH01-L000 (Figure 6).

Figure 6: The UQDLS-02HSH01-L000 socket has an integral release button and a red identification marker. (Image source: Amphenol)

The release button makes it easier to disconnect the mated plug and socket. The push-button latch socket features a flat-design button that does not extend beyond the body of the connector, making it easily accessible in confined quarters. This socket is also terminated in a 1/4 in. hose barb and includes a red identification band.

Conclusion

AI datacenters are increasingly characterized by high power density with modular liquid cooling systems. These systems require sealed, dry-break liquid disconnects in multiple sizes and termination options for safe, reliable cooling in confined spaces. The Amphenol OCP-compatible UQD and UQDB solutions meet these needs to support continuous use in environmentally demanding electronics applications.