Over the last few years a new cooling technology has taken exceptional strides toward enabling the use of commercial off-the-shelf equipment in military systems.

Until recently, most processors used in systems designed for the military did not generate enough heat to require cooling systems, aside from a fan and heat sink. Today, however, traditional cooling methods are hitting a thermal wall as processor speeds increase, creating more heat. Additionally, ruggedization efforts have become more expensive, resulting in solutions that lag farther and farther behind current technology. A new approach to cooling is being taken by designers of military systems that will allow them to utilize the latest commercial technologies, offering the most advanced systems to the warfighter. Evaporative cooling, or “phase-change” cooling, is on the leading edge of filling that need.

The Benefits of Evaporative Cooling

Traditionally, large heat sinks and fans were the main avenue for cooling heat-intensive areas of electronics, such as processors, video cards and power supplies. Due to the weight of the heat sinks attached to these components—sometimes up to 2 lbs.—a costly and time-delaying process of board “ruggedizing” has been employed so that these boards can survive the effects of the shock and vibration to which they are subjected. However, the use of evaporative cooling allows commercial equipment to bypass this ruggedization process. Instead, the latest technology can be inserted directly into the system.

Evaporative cooling uses a fine mist of non-conductive liquid, which is sprayed onto the electronics’ hot spots, where it evaporates, taking the heat with it. This process operates in a manner similar to the way that perspiration cools the human body. The vapor that results is circulated through a heat exchanger and condensed back into a liquid to be sprayed again at the beginning of a new cycle, in a closed-loop system (Figure 1).

Placing the electronics in this thermally controlled operating environment reduces heat-related failures, reduces thermal cycling and allows a much larger heat load to be cooled. This process is extremely efficient, in fact, hundreds of times more efficient than air cooling. This means that not only can higher heat loads be cooled where conduction cooling fails, but less energy is required to cool the system. Therefore, as processors continue to become more powerful, and at the same time create more heat, evaporative cooling technology is increasing the available thermal headroom, which will enable processors currently being developed to be cooled.

While evaporative cooling technology focuses on thermal control, there are many other benefits that come to the forefront when this solution is used. Without the need for large heat sinks and air channels, electronic density increases while size and weight are decreased. As a result, the amount of electronics processing can be increased by a factor of three while retaining the same footprint. Without the need for heat sinks and air channels, electronic devices can be packaged more closely together.

Another benefit is that the electronics are in a completely sealed system, which protects them from environmental factors such as sand, dirt or moisture. In many situations, as with systems deployed currently in Iraq, excess heat is compounded by plugged filters and boards covered with the talcum-like sand that severely reduces cooling and operational capabilities. Sealing these systems reduces environmental concerns because the electronics are not in contact with the outside environment.

Unlike heat sinks and fans, which reject heat at the source, evaporative cooling can reject heat away from the source. Because the vapor can be transported, the heat can be rejected at distance from its place of origin. This means that the heat does not get pushed into the surrounding area, whether inside of a tank or inside of a data center. Instead, the heat can be rejected outside of the vehicle or building, reducing the temperature around the electronics and lowering the noise levels of the fans.

The Future of Evaporative Cooling

The future of evaporative cooling technology in military applications is promising. Systems are being deployed in land, sea, aerospace and government computing applications.

One company developing and deploying this technology is ISR. Its evaporative cooling technology and products, called SprayCool, have been developed in close coordination with the military and prime system integrators (Figure 2). The first implementation of this technology in a military environment was in the Marine Corps’ Advanced Amphibious Assault Vehicle (AAAV).

Since then, just as the AAAV has been transformed into the Expeditionary Fighting Vehicle (EFV), the electronics in its evaporative cooling system have gone through three board upgrades and extensive testing. As a result of the technology’s versatility and the associated savings resulting from its use, the Department of Defense issued a Value Engineering Award to ISR. This award estimates that the company’s evaporative cooling products will save the DoD $300 million over the life of the EFV program.

These evaporative cooling products are also enabling the use of commercial equipment in other programs, such as cooling the radar electronics on the Phalanx Close-In Weapons System (CIWS). This is a fast-reaction, rapid-fire 20-millimeter gun system that provides U.S. Navy ships with a terminal defense against anti-ship missiles that have penetrated other fleet defenses.

Another example is in the work of Northrop Grumman and the Air Force on the Global Hawk Unmanned Aerial Vehicle (UAV). Here, SprayCool evaporative cooling products are performing in extreme environments from -65° to 70°C at an altitude of 70,000 feet for extended periods of time. They are also being designed into additional military programs where heat, environmental issues, noise and other factors are creating barriers to utilizing the latest commercial technology.

Evaporative cooling solutions are taking on the highest heat loads in the worst environments, while at the same time allowing the insertion of leading-edge commercial technology into military systems. Utilizing this technology will make the latest electronic systems available to the forward-deployed warfighter.

ISR
Liberty Lake, WA.
(509) 232-2600.
[www.spraycool.com].