Publication: The study of heat transfer effects on blown film molded
Date
2024-08-01
Authors
Nur Atiqah Binti Md Rautin
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Abstract
This study focuses on the effects of heat transfer on high-density polyethylene (HDPE) blown film-molded products. The experiment methodology involves precise control and measurement of bubble shape and surface temperature on the bubble using advanced video and thermal camera technologies. The study investigated the effect of processing parameters on the thickness of the film, diameter, and mechanical properties. The blown film extrusion experiment was conducted across a range of blower speeds, which are 500, 600, 700, 800, 900, and 1000 rpm, with two different compress air openings at 10° and 20°. The collected data provide an understanding of how variations in cooling rates and thermal gradients impact the structural and mechanical properties of HDPE films. Besides, the incorporation of the Churchill-Bernstein correlation further refines the understanding of the convective heat transfer coefficient, which provides a quantitative measure of heat transfer efficiency during the cooling phase of the blown film process. The main studies show that increased airflow rates increase heat transfer coefficients, resulting in thinner and more uniform-thick film. The study also shows that the faster cooling rate causes rapid solidification, which hinders the alignment of the molecular chain, resulting in lower tensile strength due to lower crystallinity. An extra study on velocity distribution across the bubble was investigated numerically by using computational fluid dynamics (CFD) simulation in order to enhance understanding of the blown film process. Velocity contours and vectors of the external cooling air at high, medium, and low axial distances was obtained throughout the simulation. The velocity contour illustrates that the higher velocity was shown near the die exit due to the constricted area and starts to decrease as the polymer moves upwards and away from the die, where the bubble is rapidly inflated. The velocity vector shows a recirculation pattern where high-axial-distance bubbles have the largest vortex vector in the recirculation flow zone. These simulations provide useful insights into the fluid dynamics, which enable the prediction and optimization of film behavior under different situations. The study also emphasizes the significance of optimizing cooling techniques and process factors in order to achieve consistent film performance.