Evaluation of non-uniform cooling effects for air-cooled forgings

The air-cooling of cylindrical bars in cross-flow and longitudinal flow was considered, as was the cooling of a stepped cylinder. The convective heat transfer coefficient significantly influenced the resulting cooling curves. Inverse methods provided a good estimate of the heat transfer coefficient only when there was no phase transformation in the specimen; they coped badly otherwise. However, the heat transfer coefficient for steel bars depended only weakly on temperature. Therefore, heat transfer coefficients measured below the temperature of phase transformation could be used to predict cooling from temperatures above it. A proprietary CFD code was also employed to estimate heat transfer coefficients. This was adequate for simple, longitudinal flows. However, it is well known that cylinders in cross-flow exhibit flow separation and recirculation, which cannot be modelled adequately.