The need for liquid cooling adoption in defense applications
The emergence of electronic and network-centric warfare has led to the rapid adoption of advanced computing solutions in the defense industry. However, as processing requirements increase, heat generation also increases. If not dissipated quickly and efficiently, excess heat can damage vital electronics. In many non-military applications the electronics industry has moved beyond passive cooling and traditional air cooling to find new ways to cool multicore processors. For instance, data centres have adopted liquid cooling, including direct to chip liquid cooling and air-to-liquid heat exchangers, to help remove heat from high-density processor and server racks.
The military electronics space is starting to face the same issue as the commercial market has – air cooling is unable to keep pace with the need for advanced data processing. Most 3U conduction cooled assemblies (CCAs) that house critical information deployed in military operations can only dissipate heat up to roughly 80W per slot, depending on the application parameters. Advanced CPUs and GPUs can run upwards of 250W-700W per chip at maximum speed, far exceeding what conduction or air cooling can handle.
The increase of SWaP (size, weight and power) requirements means more power is required in a smaller footprint. This has led to engineers to add cooling into their calculations (SWaP-C), ensuring electronics will operate efficiently even with increased heat being generated by upgraded electronics.
Cooling in the military setting
Given the various risks associated with liquid cooling, adoption into military space is not a small obstacle to overcome. Unlike in the commercial market, liquid cooling systems for defense must be able to withstand shock, impact, vibration and g-forces. Coolant cannot compress or reverse flow under g-force. Chillers must deliver consistent cooling temps in a wide range of ambient environments. Additionally, liquid cooling adds additional risk to the electronic system and can increase Mean Time Between Failure (MTBF) due to the addition of active components like pumps and compressors to the cooling system.
Despite the challenges, the need for advanced electronics, and therefore advanced cooling, will only continue to grow. The industry is already adopting liquid cooling technologies, and various industry consortiums and manufacturers are working to develop liquid cooling that dissipates the increased heat effectively while at the same time minimizing the risks associated with liquid cooling.
In aircraft and ground vehicle applications some chassis have liquid cooling at the chassis level (cold wall applications). However, this technique does not directly target the heat generated from processors. Before heat can be removed from the system at the cold wall, heat must still be conducted away from the processor, through the conduction cooled plug-in card (PIC) housing, and through the card locks to the cold wall. This heat path includes multiple resistances and material junctions between the processor and the cold wall and is limited in its efficiency and effectiveness.
Applying VITA standards
nVent SCHROFF, having deployed liquid cooling technology for over 20 years in various applications, is developing and introducing these advanced cooling techniques into the defense industry.
nVent SCHROFF sits on the VITA 48.4 working group and is part of the VITA consortium that helps to establish various standards around open systems. To help create a cooling solution that directly targets advanced processors in the defense industry, nVent SCHROFF utilized the VITA 48.4 standard.
The VITA 48.4 standard:
- provides a standard, interoperable and ruggedized architecture
- defines a standard leak-proof interconnect for coolant
- specifies a minimum 300W cooling capacity for a 6U board/module
- calls for tolerance compensating and latching injectors/ejectors
“The VITA consortium has been instrumental in providing the architectural framework for open systems for over 40 years. With industry leaders involved, the standards are well developed to provide peace of mind to users who will ultimately utilize the technology deriving from the standard,” says nVent SCHROFF Senior R&D engineer, Emerson Gutierrez.
By following the VITA 48.4 standards, nVent SCHROFF was able to develop a liquid flow through module that has coolant travel directly over processors to absorb heat and transfer the heat away from a circuit board. With the ability to customize the flow path to directly target the processors, this cooling method can cool up to 150W for 3U per slot and 300W for 6U per slot, far exceeding the cooling capacity of conduction cooled assemblies.
Liquid cooling is not only for embedded systems but can also be deployed to cool the 19” electronics cabinets found on many naval vessels, aircraft, C5ISR and mobile command centers. 19” cabinets are populated with a variety of electronics and power sources generating high levels of heat. While various air-cooling techniques (air filtered fans, air/air heat exchanger, air conditioners) are still widely used, they are limited in their ability to dissipate concentrated, high-density heat quickly.
A cooling strategy for military applications
Using lessons learned from developing efficient liquid cooling methods for data centers, nVent SCHROFF has developed ruggedized liquid cooling for cabinets and racks in the defense industry. The latest development is an air to liquid heat exchanger (Rugged LHX). The easy to install and retrofittable product, hooked up to an external chiller or water line, allows users to achieve higher computing density in new racks and existing applications.
According to nVent SCHROFF’s Vertical Growth Manager Matt Tarney, “Air-to liquid allows for greater compute density, and more efficient cooling than forced air and optimizes space in the cabinet. This technology is especially useful when new or upgraded electronics must be installed into existing 19” cabinets.”
The Rugged LHX sits at the bottom of the cabinet, pulling warm air from the rear of the cabinet into the air-to-water heat exchanger. The heat in the warm air is transferred to cold coolant flowing through a coil, then the resulting cooled air is blown into the front of the cabinet, cooling the electronics. This system has a cooling capacity of 7.5kW, a variable air flow of ~250 up to 1800m3/h and an ambient temperature range from 5OC to 50OC. Temperature can be regulated by automated remote temperature sensors or remotely from another networked device.
With this liquid cooling technology, liquid is not close to electronics, providing a reliable and safe cooling method, far exceeding the capabilities of in-rack forced air.
Whether it is at the embedded systems level or at the 19” cabinet level, liquid cooling will continue to evolve and become a major cooling strategy as electronic warfare continues to grow within the defense industry.
To learn more how nVent SCHROFF applied VITA Standard 48.4 to develop the Liquid Cooling Module, download here:
