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An experimental investigation was performed to characterize the flow field produced by a dual-lip air ring used in the blown-film manufacturing process for a solid model with a blow-up ratio of 3.5 similar to the shape of a typical LLDPE bubble. Distributions of the static and fluctuating pressure on the model and the flow field above the forming cone were measured for a range of settings on the dual-lip air ring. It was found that the distribution of the pressure on the bubble below the forming cone had many features similar to the measurements for a bubble with a blow-up ratio of 2.5 [ 1 ]. In the region above the forming cone, the upper jet appeared to merge with the lower jet rather than entraining the lower jet as was observed for a bubble with a blow-up ratio of 2.5 [ 1 ]. This resulted in a smaller local maximum in the normalized fluctuating pressure in the region above the forming cone and would likely result in less heat transfer in this region. It was also found that the initial angle of the upper jet exiting the air ring changed when the height of the bubble cone was adjusted for the bubble with the blow-up ratio of 3.5. This affected the static pressure in the region below the location where the upper jet attaches to the bubble and the pressure fluctuations in the region where the upper jet attaches to the surface. Finally, unlike the bubble with the blow-up-ratio of 2.5 [ 1 ], the presence of the bubble cone caused a region of negative gauge pressure in the region above the forming cone that should act to stabilize the bubble against the bubble cone. The pressure in this region and the region below the forming cone both decreased when the porosity of the bubble cone was reduced.

Experimental Investigation of the Effect of the Bubble Cone on the Cooling Jets used in the Blown Film Manufacturing Process