On Characterizing Air-Flow-Through Chassis: An Investigation of Manifold Flow in Rugged Electronics Enclosures

Traditional rugged enclosures utilizing forced-air cooling provide inadequate operating margins for modern, high-power modular electronics in typical military environments. VITA’s recent mechanical standard seeks to improve SWAP-C for 3U and 6U form factor plug-in modules by adopting air-flow-through (AFT) technology, namely ANSI/VITA 48.8-2017. By delivering coolant flow through the plug-in module heatframe, the conductive heat path is optimized, shifting the design objectives from maximizing convective heat transfer along a common coldwall towards obtaining acceptable flow distributions across all AFT modules with minimum supplied pressure head. Rugged chassis designs supporting AFT modules create a flow network of parallel channels which share common inlets and outlets, effectively operating as a manifold. An extensive matrix of operating conditions and compliant designs are numerically investigated with parametric design sweeps. Simulations adopt varying distributions of flow resistance that hypothetical AFT modules would produce. Z-type, U-type, and combining manifold configurations are investigated. Given the number of configurations, exclusive use of 2-dimensional steady RANS simulations is made within STAR-CCM+ commercial CFD software. Results confirm that the combining manifold avoids considerable losses associated with the delivery of flow through a header, yielding flow rates superior to U and Z-type manifolds. A positive correlation is observed between mean slot resistance and flow uniformity among slots. The adoption of ANSI/VITA 48.8-2017 is simplified by providing a thorough presentation of data, enabling critical insights into system performance for various design strategies.