Direct Spray Liquid Cooling Systems

For decades military platforms have included electronics for avionics, vehicle controls, radios, radar, sonar and fire control. From a computational standpoint most of these systems could be accomplished with relatively low power devices. There have always been higher performance electronics for applications such as radar processing, Intelligence, Surveillance, and Re - connaissance (ISR) processing, and mission computing; however, high performance electronics were relegated to stationary, benign environments. Due to bandwidth limitations of secure communications between command centers and front line troops, trends to include these computationally intense applications on vehicles and aircraft exist. From airborne platforms such as U-2 Dragon Lady and Global Hawk operating up to 70,000 feet and -65°C, to a surface-to-air missile launcher mounted on a 5-ton truck called Medium Extended Air Defense System (MEADS) in a scorching +60°C desert, the military is deploying incredible performance in harsh environments. To fit on these military vehicles, the size, weight and power (SWaP) of the electronic systems are minimized to extend the range of airborne platforms or allow ground vehicle transport with a wider range of operation. Direct spray cooling systems are enabling these programs with minimal SWaP budgets and harsh environmental requirements to use lower cost, high performance embedded electronics.

Cooling System Architecture

In practice, direct spray systems operate similarly regardless of shape, size, or application. For all systems there are three fundamental functions of a cooling system: heat acquisition, heat transport, and heat rejection. Heat acquisition is accomplished by spraying a fine mist of non-conductive and non-corrosive coolant with atomizers (orifices) directly onto electronics or within a cold plate. As the coolant vaporizes, heat is transferred from the electronics to the fluid-vapor mixture. Transport occurs when the coolant vapor condenses on the enclosure walls collecting in the reservoir. System components are often connected by drip-less “quick disconnect” fluid connectors for ease of maintenance or reconfiguration. Finally, heat rejection is accomplished via the heat exchanger that rejects the thermal load to ambient air or platform fluid. Several fluid options for heat rejection on military vehicles include Polyalphaolefin (PAO), fuel, engine bleed air, an Ethylene Glycol and Water (EGW) mixture, or ram air. Heaters are also used to heat the electronics at cold ambient temperatures.

Filtration is built into the enclosure, pump, and coolant delivery system to remove organic and chemical contamination. For mobile applications, valves are placed in the corners of the units to sense fluid and open when sufficient fluid is present. A controller is employed to operate the cooling system and provide cooling system status, user diagnostics, and warnings/shutdown notifications. Lastly, direct spray enclosures support cPCI, VME, VXS and VPX electronics in either conduction or lower cost aircooled variants.