Serrated plate fins are commonly used in the cooling of under carriage electronics in people movers and other rail transportation systems. Here, a bank of electronic equipment consisting of diods, IGBT’s, and other power and control devices reside in an electronics box attached to the under-carriage. Plate fin heat sinks are typically attached to underside and along the sides of the box; typically flow through the heat sink is regulated by enclosing the sink in a channel with an open inlet and outlet for the flow. The heat sink is shown in Fig. 1. Even though water is used for cooling in Europe, the primary cooling fluid in the United State is forced air supplied by a blower and/or by the train motion. The problem is unsteady because of the train starts and stops, changing the load on the electronics and resulting in changes in the power dissipation.