Melt-blowing of viscoelastic jets in turbulent airflows: Stochastic modeling and simulation

Abstract

In melt-blowing processes micro-and nanofibers are produced by the extrusion of polymeric jets into a directed, turbulent high-speed airflow. Up to now the physical mechanism for the drastic jet thinning is not fully understood, since in the existing literature the numerically computed/predicted fiber thickness differs several orders of magnitude from those experimentally measured. Recent works suggest that this discrepancy might arise from the neglect of the turbulent aerodynamic fluctuations in the simulations. In this paper we confirm this suggestion numerically. Due to the complexity of the process direct numerical simulations of the multiscalemultiphase problem are not possible. Hence, we develop a numerical framework for a growing fiber in turbulent air that makes the simulation of industrial setups feasible. For this purpose we employ an asymptotic viscoelastic model for the fiber. The turbulent effects are taken into account by a stochastic aerodynamic force model where the underlying velocity fluctuations are reconstructed from a k-turbulence description of the airflow. Our numerical results show the significance of the turbulence on the jet thinning and give fiber diameters of realistic order of magnitude.

Measurement and Comparison of Melt-Blowing Airflow Fields: Nozzle Modifications to Reduce Turbulence and Fibre Whipping

“…Due to it becoming a popular method due to its application on producing high-efficiency air filters in industry [ 1 , 2 , 3 , 4 ], melt-blowing technology has been of increasing interest in recent years owing to the development of nanotechnology [ 5 , 6 , 7 , 8 , 9 ]. During the melt-blowing process, polymer melts are attenuated into micro/nanofibrous nonwovens with the help of high-speed hot air jets [ 10 ].…”

Simultaneous Measurement in Nonisothermal Melt-Blowing Airflow Field: Time-Averaged and Turbulent Characteristics

“…As the most popular method for producing micro/nanofibrous nonwovens in industry, melt-blowing technology has been of increasing interest due to the growing up of nanotechnology in recent years. , Melt-blown fibers are generally of small diameter, ranging from hundreds of nanometers to a few micrometers. Owing to the large specific surface area and high porosity of the micro/nanofibrous web structure, melt-blown nonwovens are ideally suited for filtration media and oil sorbents. , The melt-blowing process involves polymer jets surrounded by high-speed hot air jets, which is accomplished by the melt-blowing die.…”

On flow-enhanced crystallization in fiber spinning: Asymptotically justified boundary conditions for numerics of a stiff viscoelastic two-phase model

“…It has also served as a test example by Shrikhande et al in [11]. All relevant physical, rheological and model parameters as well as the setup-specific reference values can be found in Appendix C. For the numerical treatment of the boundary value problems we employ a continuationcollocation scheme which has been successfully used in various fiber formation processes, see, e.g., [1,2,12,13]. For further information on the numerics we refer to Appendix D. We note that our collocation-continuation method has some advantages over the shooting approach in [7,11].…”

“…They can be expressed as polynomials in the orientational tensor component S zz , i.e., These parameters often make it difficult to solve the BVP without a good initial guess, which can be hard to find for given parameter settings. In this work we employ a collocation-continuation scheme that has been successfully used in various fiber formation problems, like glass wool production [2], melt blowing [13], dry spinning [12] or electrospinning [1].…”