Helical static-mixer insert for pediatric and neonatal gas blending: RANS-CFD comparison of commercial and in-house monolithic designs.

Accurate blending of oxygen and air in pediatric and neonatal respiratory support depends on compact connectors that promote efficient mixing without generating excessive pressure drop or dead volume. In current clinical practice, commercially available T-shaped connectors are often used as passive mixers, but their internal geometry was not originally optimized for this purpose. In this work, the original commercial connector (Geometry A), an in-house modified multi-part connector incorporating a static insert (Geometry B), and a new monolithic helical static-mixer insert (Geometry C) were evaluated under identical flow conditions. Three-dimensional Reynolds-averaged Navier-Stokes computational fluid dynamics simulations were performed to represent oxygen-nitrogen mixing in high-flow nasal cannula circuits, considering realistic flow rates and boundary conditions. For each geometry, mixture quality at the outlet was assessed from the spatial distribution of species mass fraction, hydraulic performance was quantified by the device pressure drop, and residence-time behavior for the helical insert was obtained from a transient scalar-pulse simulation. Geometry B improved outlet homogeneity relative to the commercial connector but required several assembled parts, which complicates handling and sterilization. Geometry C, designed as a monolithic helical static mixer, produced more uniform gas mixing than both previous configurations while maintaining pressure drops within ranges compatible with pediatric and neonatal use. These results indicate that the proposed helical insert has the potential to replace the current multi-part in-house adaptation and to offer a more effective alternative to standard commercial connectors when implemented as a monolithic medical-grade component.