Numerical simulation of turbulent air flow tangentially impinging on a blown film bubble has been carried out. The cooling air is assumed to originate from a dual orifice adjustable air-ring. The stream line pattern and heat flux are determined through a finite volume numerical technique using a version of the so called k-∊ modeling. It is shown that as the air flows through the air ring passage relatively large under-pressure is created (Venturi effect), which applies a suction to the bubble. Depending on the flow rates and geometrical configurations the air jet may attach itself (Coanda effect) to either the air ring surface and/or to the bubble. The Coanda effect has a significant influence on local heat flux. The numerical results suggest that the Venturi and Coanda effects influence significantly process stability, production rate and final film properties.
The present work is concerned with the numerical simulation of the blown film process and its comparison to experimental data. The bubble formation and the biaxial stretching of the film were studied using a non-isothermal, purely viscous, temperature dependent model. The model is incorporated into a software package called B-FILMCAD. Special attention has been given to the importance of the temperature in the modeling of the blown film process. It was found that temperature is by far the most important modeling parameter. The results show that the majority of the process parameters can be successfully predicted by the employed model, showing a good agreement between experimental data from various investigators and numerical predictions. This was valid for most of the studied cases despite the diversity of the experimental data. With the use of the present model many useful conclusions can be drawn about blown film production lines.
This work presents experimental meltdown-time profiles for nylon 66 and polypropylene and compares them with predictions obtained by applying the analytical model developed by Stokes [11] . A methodology is presented for obtaining approximate estimates of shear rates and temperatures developed within the molten polymer during the process. Use of the corresponding melt viscosity values as inputs in the model yielded good agreement between experimental data and model predictions. Predictions of melt film thicknesses, maximum melt temperatures, and shear rates are also presented. POLYM. ENG. SCI., 45:789 -797, 2005.
Numerical simulations of turbulent air flows tangentially impinging on blown film bubbles have been carried out. The cooling air is assumed to originate from a dualorifice adjustable air-ring. The streamline patterns and heat fluxes are determined through a finite volume numerical technique for modeling of turbulent air flow. It is shown that cooling efficiency is critically sensitive to the air-ring design as minor modifications cause large variations in cooling performance. Additionally, for a given design, the operational setup of the air ring is equally critical to the cooling performance. It is explained that the large influence observed on heat transfer rates is priinarily due to the Coanda effect, which forces air jets to attach themselves to surfaces.MTIRODUCTION he air cooling system is an integral part of any T blown film line. It greatly affects not only the heat transfer from the molten polymer film but also the stability and the shaping of the bubble. Several researchers (1-5) have examined the importance of the heat transfer in the modeling of film blowing. Film cooling ultimately affects both production rate and final film properties.Two important aerodynamic phenomena are associated with the cooling airflow, namely the V e n t w i and C o a d a effects. The well known Venturi effect is caused when a fluid flows through a constricted area: its speed increases and the pressure drops (Rg.
Numerical simulation ofturbulent flow ofjet impinging at various angles on blown film bubbles has been performed. The air flow from various types of air rings has been studied. The streamline pattern for external cooling as well as heat transfer coefficients have been detennined from the solution of the differential equations for the conservation of mass, momentum and energy of the air jets studied. The turbulent flow has been calculated using the renormalization group (RNG) k-E model. Venturi effect (local creation of low pressure due to high speed flow at narrow passages) has been studied.
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