There’s just no avoiding the trend toward processors and other key components ramping up in wattage. That ever increasing power means more challenges dissipating heat. Exotic techniques such as spray cooling and liquid cooling are all on the table as possible ways to attack the cooling challenge. As a result, military system designers are being compelled to weigh the complex risks and advantages involved in staying with evolutionary cooling approaches versus embracing newer, more exotic forms of controlling the thermal environments of their embedded systems. To keep pace, vendors of chassis and complete system-level solutions have begun to craft solutions designed from the ground up to use innovative cooling approaches.

At the board level, power increases are likewise expected to climb as military systems continue to crave greater compute density and shift to high-speed serial technologies via the emerging form factors like VPX (VITA 46). VITA 46 for its part allows up to 768 watts of power on a 6U x 160 mm board. That’s a major increase over the 90-watt limit allowed on VME cards, but it poses a substantial cooling challenge to design engineers.

2U Chassis Solution

Rolling out a chassis solution, Triple E recently added a new 2U microchassis (Figure 1) to their line of enclosures for military and aerospace harsh environment applications. The rackmount unit features a flange that spans the entire depth of the unit, two fans and patented all-aluminum guide decks. This unique combination of features provides exceptional stability to protect boards from vibration damage, incorporates superior left to right cooling and maximum airflow between slots for protection against heat build up all while supporting the weight of the unit in a 2U package size.

The units are constructed from 0.036-in. zinc-plated steel with black powder coat finish for added strength and durability. The unit includes 3U, 300W PICMG 2.11-compliant dual redundant power supplies incorporated within the 2U aperture. Efficient cooling is achieved with two high-speed 12V DC 84CFM fans in push-pull configuration that are attached to side rack angles for easy serviceability. Sensors are located to monitor PCB and PSU temperature and are connected to a fan controller to maintain optimal operating temperatures.

Liquid-Cooling Systems

Liquid cooling–long considered too risky for military systems–has begun to gain mindshare in the defense realm. Liquid cooling relies on a naturally abundant medium, is environmentally friendly and enables the processing of massive amounts of energy. TDI Power’s latest liquid-cooling solution is its Liquid Cooled Mercury Shelf (Figure 2). When combined with its standard fan-cooled Mercury rectifier modules, the shelf is designed to be part of a high-power DC system. Each 2U shelf is self-contained with an input AC connector and an output DC Terminal Block. The shelf also has inlet and outlet connectors for the cooling liquid and an alarm and control connector. Using the self-cooled rectifiers’ fan to force the waste heat (from the rectifiers) through the integral cooling element, the system releases very little heat outside of the shelf. Shelf-cooling is completed via the internal Heat-Exchanger with an external coolant chiller.

Where once relegated to a custom-only offering, system-level solutions geared specifically with cooling features have started to emerge as off-the-shelf products. Along just such lines is Themis’ CoolShell product line (Figure 3). The CoolShell product line includes Slice, in liquid flow through and air-cooled configurations, and Slice-CT in its several height variants. This product family shares a common theme. This system offers modular, sealed and self-cooled 1RU-high Field Replaceable Units (FRUs), which blind mate into a minimalist power and network backplane. The product families each have passive subracks that house the constituent FRUs. All active components, including fans/blowers are field replaceable from the front of the rack and all external interconnects, I/O and Power have front panel access. Cooling is front-to-back and all slots have independent, active airflow control. FRUs utilize “exoskeleton” clamshell or truss plate, patent-protected Themis technology to ensure high shock and vibration resilience.