中国塑料 ›› 2020, Vol. 34 ›› Issue (10): 56-62.DOI: 10.19491/j.issn.1001-9278.2020.10.010

• 加工与应用 • 上一篇    下一篇

加热过程的滚塑模具内表面传热系数的计算

刘学军1, 江辉2   

  1. 1.北京工商大学人工智能学院,北京 100048
    2.温岭市旭日滚塑科技有限公司,浙江 温岭317511
  • 收稿日期:2020-04-10 出版日期:2020-10-26 发布日期:2020-10-26

Calculation of Heat Transfer Coefficients at Internal Surface of Rotational Mold in Heating Process

LIU Xuejun1, JIANG Hui2#br#   

  1. 1.School of Artificial Intelligence,Beijing Technology and Business University,Beijing 100048,China
    2.Wenling Rising Sun Rotational Molding Technology Co,Ltd,Wenling 317511,China
  • Received:2020-04-10 Online:2020-10-26 Published:2020-10-26

摘要:

给出了2种计算加热过程的圆筒形滚塑模具内表面传热系数的方法。第一种方法是利用模具表面和内部温度的实测值通过模具内部空间的热平衡方程计算出其内表面传热系数。第二种方法是借用回转窑内物料与壁面间传热系数的理论公式来计算滚塑模具内表面的传热系数。在模具内部无粉料和装有0.21 kg粉料的情形下,分别用这2种方法计算了模具内表面瞬时的传热系数和平均的传热系数,并应用流体力学的边界层理论解释了内表面传热系数随时间的变化规律。然后将第一种方法计算所得的平均传热系数整理成努塞尔数与普朗特数的无量纲准则式Nu= 45.73 Pr -0.55,其适用条件为绕中心轴转动的轴向长度大于内径的圆筒形滚塑模具。结果表明,随着模具内装有粉料的体积百分比的增大,其内表面的平均传热系数减小,同时上述2种方法计算的平均传热系数也吻合得越来越好;如果粉料的体积百分比不低于62.4 %,那么第二种方法计算结果的相对误差不超过20 %。

关键词: 滚塑模具, 加热过程, 内表面传热系数, 热平衡方程, 无量纲准则式

Abstract:

In this work, two methods were adopted to calculate heat transfer coefficients at the internal surface of a cylindrical rotational mold in the heating process. In the first method, the test temperatures at the mold surface and inside were adopted to calculate heat transfer coefficients at the internal surface of the mold via a heat equilibrium equation for the internal space of the mold. In the second method, the formula for the heat transfer coefficients between the powder material in the rotary kiln and the kiln wall was used to calculate the coefficients at the internal surface of rotational mold. Both of the methods were used to calculate instantaneous and average heat transfer coefficients at the internal surface of the mold in the cases of no powders and powders of 0.21 kg loaded. The boundary layer theory of fluid mechanics was applied to explain the variation of heat transfer coefficients at the internal surface with time. The average heat transfer coefficients obtained by the first method were processed in the form of a dimensionless correlation of Nu with Pr Nu= 45.73 Pr-0.55). The correlation holds for a cylindrical rotational mold with its axial length larger than inner diameter, which rotates along its central axis. The results indicated that the average heat transfer coefficients at the internal surface decreased with an increase of the volume percentage of powders inside the mold. The results calculated by the above two methods were found to be in good agreement with each other. The relative error of calculated results by the second method was less than 20 % as long as the volume percentage of powders was higher than 62.4 vol %.

Key words: rotational mold, heating process, heat transfer coefficient at internal surface, equation of heat equilibrium, dimensionless correlation

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