Abstract:

In this study， two research methods were proposed to assess the heat transfer coefficients at the inner surface of a rotational mold heated by electricity. These two methods were suitable for the heating phase just before the powders started to melt. In the first method， the temperatures at the outer surface and inside of the mold were measured in the four cases. Then， a heat transfer model was established based on the energy conservation law so that these tested temperatures could be converted into heat transfer coefficients at the inner surface of the mold in the four cases by means of the model. In the second method， the actual rotational mold was simplified to a two⁃dimensional cylinder equivalently. The air inside the mold was treated as a main phase， and the powders were treated as a secondary phase. The numerical simulation was conducted to calculate the heat transfer coefficients at the inner surface of the mold with the aid of the Mixture model in the multiphase module of the FLUENT software. The results obtained from these two methods were in good agreement with each other in the three cases. As the volume percentage of powders increased， the heat transfer coefficient at the inner surface of the mold increased rapidly at first and then tended to increase slowly. It started to decrease after reaching a peak value of 61.2 W/（m²·K）. At the inner surface of the mold， the errors of heat transfer coefficients caused by the second method were no more than 10 % when the volume percentage of powders was out of the range of 58 %~74 %.

Key words: rotational mold, heating phase, heat transfer model, heat transfer coefficient at inner surface, FLUENT simulation