BEYOND THE DATASHEET
/ NEW CONNECTORS FOR LIQUID COOLING
By Philip Ling Technical Content Manager, Avnet
Look behind the datasheet of the connectors designed to carry liquid coolants around high-performance computing systems, EV chargers and more.
BEYOND THE DATASHEET
/ NEW CONNECTORS FOR LIQUID COOLING
By Philip Ling Technical Content Manager, Avnet
Look behind the datasheet of the connectors designed to carry liquid coolants around high-performance computing systems, EV chargers and more.
Using liquids for heat exchange isn’t new in the industrial, aerospace and automotive industries. Moving parts get hot quickly, and liquids are good at removing that heat to a cooler location. Now, as the power dissipation in servers climbs above the 10s and into the 100s of kWs, it’s time to use the same approach but for a different technology.
Solid-state circuits also have moving parts; electrons and holes carry current through and between transistors. That movement generates heat locally at the transistor junctions where the electrons and holes meet. Liquid can remove heat more effectively than air, but neither can come in direct contact with the junctions, so the heat needs to first travel through the integrated circuit packaging.
Thanks to physics and good design, heat likes to move to cooler regions, which are normally external surfaces. Once there, it can move to another medium, such as air or liquid. Removing heat fast enough to keep the junctions within their operating limits is critical. Liquid is a more efficient medium than air, but mixing liquid and electronics comes with complications.
Depending on the implementation, the liquids used may not be dielectric (non-conductive), so there are some baseline requirements that connectors need to meet. Leak-free is one, high flowrate for a given size is another. Both impact the connector’s design.
The UQB and UQDB series of liquid cooling connectors from Amphenol exceed the specifications created by the Open Compute Project (OCP). The UQB series offers quick-connect technology, while the UQDB features blind mating for easy installation. Both use high-performance, aerospace-grade sealing materials, and bidirectional shut-off valves and dry-break sealing to protect against spillage and drips. Stainless steel is used for component longevity by impeding corrosion.
Industry specifications for liquid cooling
The UQB/UQDB connectors comply with the OCP Universal Quick Disconnect specification, which covers non-combustible single-phase systems for liquid-cooling electronics. Single-phase means the fluid used is always in its liquid form. In a two-phase system, the fluid would vaporize and condense. This process draws more energy and transfers heat more effectively, but it is considerably more complex.
Single-phase systems include:
- Direct-to-chip. In this configuration, a cold plate is bonded to the integrated circuit’s package, as a conventional heat sink might be. Coolant flows inside the plate to remove heat from the chip.
- Rear-door heat exchangers. Often called a hybrid approach, the physical rear door of a server is replaced with a door with coolant running through it. The hot liquid then passes through a heat exchanger, normally located outside the building.
- Immersion cooling. In this configuration, boards are submerged in a thermally conductive but electrically insulated liquid.
In each case, the liquid used will likely be deionized water, propylene glycol or synthetic oil. These liquids are safe, non-toxic and have good heat transfer characteristics with a high boiling point. In a two-phase system, the coolant will have a low boiling point and will often be fluorocarbon-based.
Using liquids for heat exchange isn’t new in the industrial, aerospace and automotive industries. Moving parts get hot quickly, and liquids are good at removing that heat to a cooler location. Now, as the power dissipation in servers climbs above the 10s and into the 100s of kWs, it’s time to use the same approach but for a different technology.
Solid-state circuits also have moving parts; electrons and holes carry current through and between transistors. That movement generates heat locally at the transistor junctions where the electrons and holes meet. Liquid can remove heat more effectively than air, but neither can come in direct contact with the junctions, so the heat needs to first travel through the integrated circuit packaging.
Thanks to physics and good design, heat likes to move to cooler regions, which are normally external surfaces. Once there, it can move to another medium, such as air or liquid. Removing heat fast enough to keep the junctions within their operating limits is critical. Liquid is a more efficient medium than air, but mixing liquid and electronics comes with complications.
Depending on the implementation, the liquids used may not be dielectric (non-conductive), so there are some baseline requirements that connectors need to meet. Leak-free is one, high flowrate for a given size is another. Both impact the connector’s design.
The UQB and UQDB series of liquid cooling connectors from Amphenol exceed the specifications created by the Open Compute Project (OCP). The UQB series offers quick-connect technology, while the UQDB features blind mating for easy installation. Both use high-performance, aerospace-grade sealing materials, and bidirectional shut-off valves and dry-break sealing to protect against spillage and drips. Stainless steel is used for component longevity by impeding corrosion.
Industry specifications for liquid cooling
The UQB/UQDB connectors comply with the OCP Universal Quick Disconnect specification, which covers non-combustible single-phase systems for liquid-cooling electronics. Single-phase means the fluid used is always in its liquid form. In a two-phase system, the fluid would vaporize and condense. This process draws more energy and transfers heat more effectively, but it is considerably more complex.
Single-phase systems include:
- Direct-to-chip. In this configuration, a cold plate is bonded to the integrated circuit’s package, as a conventional heat sink might be. Coolant flows inside the plate to remove heat from the chip.
- Rear-door heat exchangers. Often called a hybrid approach, the physical rear door of a server is replaced with a door with coolant running through it. The hot liquid then passes through a heat exchanger, normally located outside the building.
- Immersion cooling. In this configuration, boards are submerged in a thermally conductive but electrically insulated liquid.
In each case, the liquid used will likely be deionized water, propylene glycol or synthetic oil. These liquids are safe, non-toxic and have good heat transfer characteristics with a high boiling point. In a two-phase system, the coolant will have a low boiling point and will often be fluorocarbon-based.
Coolant distribution units
The implementation of liquid cooling can vary. In-row cooling uses one coolant distribution unit for a row of server racks standing alongside the racks. In-rack cooling integrates the coolant distribution unit into the rack, putting the coolant much closer to the hottest components.
The coolant distribution unit (CDU) is the heart of any liquid cooling system. The primary components of any CDU comprise pumps, pipes and manifolds to move liquids around, a heat exchanger, a filtration system, a control unit, and sensors to maintain flow and pressure, monitor temperature and detect leaks.
The heat exchanger is a key component, and its form will depend on whether the system uses liquid-to-liquid cooling or liquid-to-air. In a liquid-to-liquid system, the hot coolant flows through assemblies that are in contact with other assemblies carrying cool water, typically sourced from the facility’s own water supply. Heat passes, via the surfaces, from the hot coolant to the cooler water. The now warm water is then pumped out of the CDU.
The rate of heat exchange depends on the heat transfer coefficient. This is based on the heat flux of the materials used, measured in watts per square meter, and the difference in temperature of the liquids and materials exchanging heat.
Liquid cooling is already being used in high-performance computing, data centers and electric vehicle charging equipment. With new solutions like Amphenol’s UQB and UQDB connectors coming to market, expect more innovation in this area.
Learn more about the benefits of liquid cooling here, and discover how Avnet Integrated Solutions can help you implement your own future-proof solutions.
Liquid cooling is already being used in high-performance computing, data centers and electric vehicle charging equipment. With new solutions like Amphenol’s UQB and UQDB connectors coming to market, expect more innovation in this area.
ABOUT THE AUTHOR
Philip Ling
Technical Content Manager, Avnet
Philip leads our FAE roundtable discussions and develops content covering the full range of technologies supported by Avnet.
Philip has more than 30 years of electronics industry experience, including working as a design engineer on mixed-signal embedded systems. He was also a technical journalist and editor covering the industry for several European technical magazines. He has worked for small, medium and large companies as well as startups, and is pleased to say he is constantly learning.
He holds a post-graduate diploma in advanced microelectronics.