在加热阶段滚塑模具内表面传热系数的两种研究方法

Two research methods for heat transfer coefficient at inner surface of rotational mold in heating phase

提出了获得电加热滚塑模具内表面传热系数的两种研究方法,这两种方法适用于模内粉料开始熔融前的加热阶段。第一种方法是首先在4种情形下测量该滚塑模具的外表面温度和模内温度,然后根据能量守恒原理建立一个传热模型,并通过该模型将这些实测的温度值转换为在这4种情形下模具的内表面传热系数。第二种方法是将实际的滚塑模具等效地简化为一个二维圆筒,将模内空气当成主相流体,粉料当成第二相流体,通过FLUENT软件的多相流模块中的Mixture模型进行仿真计算以得到模具内表面的传热系数。结果表明,这两种方法所得的结果在其中的3种情形下都吻合得很好。随着模内粉料的体积百分比的增加,模具的内表面传热系数先是快速增大,然后增大的速率变慢,在达到最大值61.2 W/(m^(2)·K)后开始减小。当粉料的体积百分比不在58%~74%的范围内,由第二种方法仿真所得的模具内表面传热系数的相对误差不超过10%。

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/(m^(2)·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 %.