The transformers in aircraft power conversion are often very heavy and represent a significant fuel or range penalty. Being thermally sized, improved cooling methods would allow downsizing and thereby reduced weight. Since the conductive paths in these metal “dense” devices are good, the controlling thermal resistance is typically the convective coefficient. The goal of this study was to optimize the convective air cooling across transformers by parametrically testing candidate shroud geometries to minimize average and hot spot surface temperatures with minimal fan power. Experimental results from a low velocity wind tunnel were well correlated by CFD modeling, providing confidence in continued shroud development with only CFD or experimentally. A simple cubic test block was selected as surrogate to generalize and simplify both test methods and results. A new “goodness” parameter was developed that included both the heat transfer performance and pressure penalty for a comparative index of shroud designs.
The work was divided into two phases. Phase-A used numerical modeling to study a variety of different shapes to select the best for experimental testing. Phase-B included the testing and further parametric evaluation with CFD studies. A parameter was developed that quantified the effect of conductive spreading on the test article surface.
Presented here are the results of these studies, where several general shroud shapes emerged as high performance in comparative evaluation. Following the down select, specific geometrical dimensions relative to the duct and mock transformer sizes were further optimized.