(Air Transport Rack or Austin Turnbull Radio) applications have performance demands that are continuously increasing to provide the capabilities for C4ISR, electronic warfare, RADAR, and similar systems. This typically means hotter boards. The challenge for the chassis designer is to cool these heat-intensive modules effectively and do it in as little space as possible.
Even as processors are providing more performance with lower TDP (Thermal Design Power), the desire for higher wattage modules in conduction-cooled ATRs remains. It is not uncommon for OpenVPX boards to be selected that range from 75-110W. Where an external air source is supplied, it helps the chassis provider with a lot more options to cool the chassis. But, more commonly the chassis would need to generate its own supplemental airflow with fans. On the higher end of the spectrum, some OpenVPX ATR design requirements are ranging from 500-800W. These designs often have several cards with 7-12 payload boards. The unit can utilize multiple heat exchangers in an external shell that encompasses the internal sealed frame. The airflow passes over the fins and is pulled out the rear of the system. At times, heat pipes can be utilized that allow additional focused airflow in hot spots.
FloTherm thermal simulations can give indications of where minor adjustments can be made to provide optimal cooling. For example, the chassis/backplane designer can widen the spacing of the slots, change the fan configuration, use wider fins, or change the enclosure dimensions slightly. In fact, there are several elements that the chassis manufacturer needs to review to optimize the cooling. This includes:
- Chassis Material & Finish
- Fin characteristics
- Ambient temperature, altitude, humidity
- Cold plate temperature
- Wall thicknesses
- Size of the enclosure
- Slot spacing
SOSA (Sensor Open System Architecture) will utilize OpenVPX profiles in a flow-through-module cooling approach. But, by employing creative design techniques, high-power systems can be cooled with more conventional techniques.
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