聚乳酸吹膜过程中传热系数的研究

Study of Heat Transfer Coefficient in Film Blowing of PLA

通过Fluke热像仪采集聚乳酸(PLA)在挤出吹膜过程中的温度场,研究冷却风风量(Q_v)及吹胀比对PLA吹膜过程中对流-辐射联合传热系数(h)的影响,同时对传热系数在低Q_v下和高Q_v下随高度的变化进行了拟合。结果表明,随着Q_v增大,温度下降速率增大;低Q_v下(Q_v=0,0.66 L/s),随着Q_v增大,h变化不明显;高Q_v下(Q_v=1.32、2.00 L/s),随着Q_v增大,在距口模出口高度(Z)为0~0.03 m内h增大明显;随着吹胀比的增大,温度下降速率增大,在口模位置处h增大明显;在不同Q_v下,h可近似表示为高度Z的函数。

The cooling process of film blowing of poly(lactic acid)(PLA) was studied.The temperature at the outside surface of the bubble was measured as a function of vertical distance from the die by an infrared pyrometer.The heat transfer coefficient(h) was studied at different airflow rate(Q_v) and blowup ratio.The correlation between heat transfer coefficient and axial distance was also reported.It was found that the temperature decreased quickly with increasing airflow rate.At low airflow rates the heat transfer coefficient changed a little.At high airflow rates,the heat transfer coefficient inside the air ring increased with increasing airflow rate.With increasing blowup ratio,the rate of temperature decrease became larger,and the heat transfer coefficient inside the air ring became higher,h could be described as a function of the axial distance(Z).