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w w w. m r c y. c o m WHITE PAPER This paper considers these air-cooling architectures, which at first glance may seem to be the most mundane, but are actually the most interesting due to the nature of the cooling fluid. Air-Cooling (ANSI/VITA 48.1) Air-cooling may be sub-divided into CFM and air management cooling approaches. A CFM, or "cubic feet per minute" approach is the most traditional option available (ANSI/VITA 48.1) and is in wide-spread use within many commercial, development and other applications that are deployed within relatively benign environments. This approach relies upon fans to push cooling air across the OpenVPX modules to remove their generated heat. Easy to implement and understand it is also the most inefficient of the VITA cooling options as the air, like all fluids takes the path of least resistance, often avoiding the high-sky lines of the hot processors. Air Flow-By™ (ANSI/VITA 48.7) Air Flow-By (ANSI/VITA 48.7) uses an air management approach of cooling instead of a CFM method. Rather than pointing an unmanaged air stream across the modules, Air Flow-By uses a plenum (reservoir) of pressured cooling air which is directed (managed) across each module. Air Flow-By modules are sealed (EMC and environmentally) units that fit snuggly within the chassis and without further consideration would block any air flow all together. The effectiveness of Air Flow-By is achieved by introducing air passageways across the surface of each module. These channels regulate where the cooling occurs, and how much cooling is applied. In effect, the full cooling potential of the air reservoir is utilized and efficiently applied to where the heat is known to be generated. Air Flow Through treats the cooling aperture equally and is unable to prioritize the air flow within the module, removing the ability to concentrate (manage) air flow to specific hot-spots. OpenVPX is the defense and aerospace industry's de facto rugged compute architecture OpenVPX was introduced to the VME International Trade Association (VITA) Standards Organization (VSO) by a consortium of companies led by Mercury Systems in January 2009. Since its ratification, the standard has become known as the go-to standard whenever the best commercial processing technology needs to be packaged into rugged, interoperable, modular packages that have been optimized for size, weight and power (SWaP) performance. Increasingly, OpenVPX is known for its advanced and efficient cooling technologies, making it even more suitable to scalable compute applications that can be deployed anywhere. OpenVPX (ANSI/VITA 65) has been widely adopted for industrial, transportation and other rugged compute applications, and most notably for defense and aerospace applications. Within the defense domain, OpenVPX is the base standard that higher level architectures, including Sensor Open Systems Architecture (SOSA), Future Airborne Capability Environment (FACE) and Common/C4ISR/EW Modular Open Suite of Standards (CMOSS) are based. 6U OpenVPX processing system using Air Flow-By cooling architecture Conduction, air and liquid cooling architectures are available within the OpenVPX ecosystem. Whereas the air-cooling technologies have similar sounding names, their underlying technologies, implementations and overall characteristics vary significantly. ANSI/VITA Standard Description 48.1 Air-cooled 48.2 Conduction-cooled 48.5 Liquid-cooled 48.7 Air Flow-By 48.8 Air Flow Through Front panel EMI gasket Rugged, effective IEEE1101.10 injector/ ejectors Gasket seal plate Mezzanine card (Fits within standard 1-inch pitch OpenVPX slot) Primary heatsink (Component side) Secondary heatsink (PCB side) Heat spreader Air Flow-By module construction (3U OpenVPX) 2

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