Numerical simulation for circular free jet of coagulation bath
The microstructure of the hollow fiber membrane prepared by the dry jet wet spinning method based on non-solvent phase separation is closely related to the flow field structure of the solidification bath.A common solidification bath flow renewal is similar to a circular free jet.The flow field structure not only affects the stability of solution spinning,but also affects its double diffusion behavior during the membrane phase separation formation.An appropriate turbulence model can improve the accuracy and reliability of the calculation.Nine turbulence models were used to numerically simulate the circular free jet flow.The parametric results such as fluid velocity distribution,initial section length,turbulent kinetic energy(k),and entrainment under different models were obtained,and compared with the experimental values and theoretical solutions.The results show that the Launder and Sharma(LS)model,which adds additional items(D,E)to k and turbulent kinetic energy dissipation rate(ε),has the most accurate prediction of the velocity distribution.The average error of axial dimensionless velocity is 7.14%.The average error of the starting segment length is the smallest compared with the experimental value,which is 10.7%.The Prandtl number σk has a great influence on water flow diffusion.The prediction ability of the velocity distribution of the LS model can be improved by regulating the correction coef-ficient σk,and the average relative error is the smallest(2.75%)when σk is 0.15.The average error of the prediction of the turbu-lence entrainment volume under the condition of Reynolds number=6 378.2 is 3.57%.In numerical simulation of solidification bath with circular free jet,LS model is recommended.
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