熔喷双槽形喷嘴气体射流流场初探

在熔喷非织造布加工中，气体射流作为工作介质使聚合物熔体实现拉伸，气体射流流场的研究对熔喷气流拉抻数学模型研究非常重要。熔喷双槽形喷嘴形成的流场可以看作两股平面射流的合成。从单个点涡的性质出发，研究了涡偶的性质和涡偶代替射流的可行性。研究表明，在喷丝孔轴线附近，涡偶和射流的速度分布趋势相同，且有比较相近的速度分布，从而说明以涡偶代替射流是可行的。在此基础上，用两个涡偶分别代替两股射流，然后进行合成，推导出两股射流合成后速度分布的理论公式，该公式的计算结果与实验结果吻合较好。将该公式引入熔喷气流拉伸数学模型，预测出的纤维直径与采用经验公式时的预测结果几乎完全相同。结果表明，应用涡偶代替射流推导出的气流速度分布公式能够较好地描述熔喷双槽形喷嘴气体射流流场，可以用于完善熔喷气流拉伸数学模型。

Study on Flow Field of Air Jet from Dual Slot Die in Melt Blowing Process

In the melt blowing nonwoven process, the air jet draws the polymer melts into microfibers. Study on the flow field of the air jet is very important to the study on the air drag mathematical model of melt blowing. The flow field of the air jet from dual slot die in melt blowing process can be considered as the synthesis of two plane jets. The properties of vortex pair and the possibility of substituting jet with vortex pair are studied according to the nature of single vortex . The results show that the velocity distributions of these two flows have the same tendency and these two flows have similar velocity distributions near the axis of spinneret. So it is feasible to substitute jet with vortex pair. Then the two jets are substituted with two vortex pairs separately. As a result, the synthesis of two jets can be realized. The formula of the air velocity distribution after the synthesis of two jets is developed. The computing results of this formula tally with the experiment data well. The formula is introduced into the air drag mathematical model of melt blowing. By using this formula the model prediction of fiber diameter coincides with that using the empirical formula put forward by Harpham and Shambaugh. The results show the formula of air velocity distribution developed by substituting jet with vortex pair can describe the flow field of the air jet from dual slot die in melt blowing process and can be used to consummate the air drag mathematical model of melt blowing.