Fan Positioning and Configuration Considerations
Fans are frequently deployed in PXI/PXIe chassis on the bottom of the chassis interior.
Irrespective of location, airflow can normally be generated by fan outflow or fan intake, based on the direction of rotation. If outflow is employed, airflow velocity is increased. But control of the airflow's path can be difficult, and, according to PXI specifications, airflow must pass the module from bottom to top such that heat is dissipated through top vents, potentially compromising critical environments (see Figure 3). If fan intake is employed, airflow velocity is lower, but airflow is steadier and more easily controlled.
The airflow pathway must also be considered in fan configuration. Avoiding additional sources of heat and effectively exhausting cool air are major considerations for chassis design. Many users adopt hybrid test systems, installing their PXI/PXIe systems in a system rack cabinet. In this case, potential heat sources across the entire hybrid test system demand attention, not just the PXI/PXIe system itself.
When fans positioned in the rear of the PXI/PXIe chassis draw air in from the exterior and then exhaust it through the front of the chassis, the possibility exists for air heated by neighboring systems to be drawn in and forced over the PXI/PXIe modules, thereby creating an obvious disadvantage in the cooling of the overall system. Newer PXI/PXIe chassis designs use rear-mounted fan designs that channel unheated air from the front through the PXI modules, into the back of the chassis, and then out of the system, thereby maintaining intended levels of dissipation efficiency.