Inclined Fins for a More Efficient Heat Sink

This paper describes a heat transfer analysis and experiments which were performed on electronic circuit packs within an equipment frame in a natural convection environment. The specific purpose of the study is to thermally characterize a particular means of cooling circulit packs: i.e., use of large heat sinks attached to the circuit pack printed wiring board (PWB), and the use of straight fins on the heat sink, inclined at an angle from the vertical. These techniques are evaluated at the circuit pack level in units stacked four packs high. An experimental program characterized the overall heat transfer from circuit packs which simulated circuit packs in a stacked configuration in a frame. To understand the relevant heat transfer mechanisms involved, an analysis was performed to quantify the relative contribution of inclined fins. The study concluded that the internal heat sink with inclined fins can be worthwhile for certain geometries. For the particular configuration that was tested, there was a 15 percent reduction in thermal resistance over that of vertically aligned fins. Inclined fins increase the heat transfer performance as the length-to-height aspect ratio of the heat sink decreases (i.e., tall, narrow heat sinks have the most potential for improved performance with inclined fins). For a range of physical configurations, inclined fins decrease the heat sink and air temperature rises for a stack of units in a frame.