Effects of Temperature and Geometry on the Flow Field of the Melt Blowing Process

Converging plane jets are used commercially to produce polymeric fibers in the melt blowing process. The behavior of the air flow below the die face is critical for the production process. The die configuration can affect this flow field. Previous work has studied the effects of changing the angle of convergence of the two jets for blunt and sharp die faces, as well as the case of recess or excess (inset or outset) positioning of the sharp die nose for isothermal flow conditions. This study utilized a computational fluid dynamics approach that was validated through experimental data to investigate the effects of nonisothermal conditions on the air flow. The Reynolds stress model was used to simulate the turbulence, and the model parameters were calibrated with the experimental data. The behavior of alternative die designs was also correlated to the die configuration. It was found that, similarly to the isothermal case, the sharper the angle of convergence, the higher the mean air velocity under the die and the higher the intensity of the turbulent velocity fluctuations. The flow field exhibits a self-similar region beyond the point at which the flow from the two jets merges. It was found that the mean temperature and the mean velocity field beyond the merging distance can each be described by a single correlation. In these correlations, the merging distance was used as the length scale, and the mean flow velocity at the merging point was used as the velocity scale.