A Study of Heat Transfer in the Blown Film Process

Abstract

The air ring design directly affects the aerodynamic phenomena in the film blowing process. In this study, the effects of impinging jets on heat transfer are explored taking into account the influence of cooling on the bubble shape, by comparing the characteristics and performance of flows produced by single and dual orifice air rings. The aerodynamic characteristics of air-cooling flow around the bubble surface are investigated utilizing a finite volume numerical method and renormalization group (RNG) theory based on the k—ε turbulence model coupled with enhanced wall treatment method of the FLUENT commercially available software. The numerical analysis provided a detailed description of fluid flow pattern as well as heat transfer coefficients for different air ring designs, and under different processing conditions. The results of calculation indicate that the heat transfer rate critically depends on the air ring design. A simple correlation for the heat transfer coefficient and the maximum air velocity function (i.e., h = aVb max proposed in the literature) was established. The boundary conditions dominated by airflow rates are equally important for cooling efficiency. The correlation between Reynolds number and the heat transfer in the numerical solution is also reported.