There are many electronic equipments are cooled by forced cooling airs. Some equipment’s forced cooling air is supplied by air ducts, where air blower is located at a distance. In many cases, when the remote blower is out of order, the buoyancy of heated air cannot generate enough pressure to overcome the long air ducts and the blower. There is no air flow at all through the normal cooling air duct. That is called loss of cooling thermal condition. Loss of cooling condition is usually the worst case thermal challenge. In aerospace applications, most forced convection cooled electronic equipments need to meet the loss of cooling operation requirement. During loss of cooling, the electronic equipment needs to obtain cooler ambient surrounding air from a different inlet other than the supply air inlet. However, the passive cooling air inlet cannot interfere with the normal cooling situation. In normal cooling situation, forced cooling air is provided to lower the electronics temperature to a level of meeting the mean time between failure (MTBF) requirements. This paper will discuss a few trade studies of how different design approaches meet this loss of cooling air challenges; present a detailed CFD calculation of one of the design options. Many other considerations are also to be presented other than just thermal design concerns.

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