CFD-Based Extensional Stress and Hemolysis Risk Evaluation in the U.S. Food and Drug Administration (FDA) Benchmark Nozzle Configurations

Hemolysis, or the breakdown of red blood cells, observed in medical devices has been a significant concern for many years, particularly when mechanical stress on the cells is considered. This study focuses on evaluating extensional stresses in two configurations of the U.S. Food and Drug Administration (FDA) nozzle: the Gradual Cone (GC) and Sudden Contraction (SC) models. The nozzle geometries were created as 3D models using Ansys Fluent 18.2 and its pre-processing software ICEM CFD. The mesh was constructed with hexahedral elements with O-grid topologies. Effects of varying flow conditions were observed by modeling five experimental cases of the FDA nozzles, including throat Reynolds numbers of 500, 2000, 3500, 5000, and 6500. Hemolysis potentials of FDA nozzle configurations were examined by analyzing the whole domains. Turbulent modeling was used by applying the shear stress transport k-ω (SST k-ω) model. A threshold of 2.8 Pa for extensional stress was observed. Moreover, the most commonly used power law models were applied to the FDA nozzle to see the effect of extensional stress on power law models. Zhang’s power law models gave the lowest standard error, while Giersiepen’s model gave the highest error on hemolysis predictions.