Experimental characterization of pressure loss through EMI shields and 1RU card passages in dense electronic enclosures

Experimental measurements were made of the overall pressure loss coefficients of individual EMI shield samples and various printed circuit boards in a 1RU channel. The loss coefficients of the boards were highly dependent on electronic component population density. The loss coefficients of the grill samples compared surprisingly well with literature data for perforated plates, despite being taken at much lower Reynolds number than the literature data. Assemblies of printed circuit boards with upstream and downstream grills were predicted well by a 1D flow network model, but it appears that the upstream grill may influence the losses across the downstream board. The individually measured loss coefficients were used in a flow network model of an entire 9RU enclosure, with and without a fan tray present. The 1D predictions were generally adequate, except in the case with a deadlocked fan tray placed in front of the exit grill. This may be because the fan tray has a significant influence on the loss coefficient of the exit grill. The data generally showed that turbulence and flow non-uniformity generated by upstream components may influence the loss coefficients of downstream components. These interactions are generally not captured by standard 1D modeling approaches.