Numerical simulation and analysis of multiphase flow through fiber array structure in extracorporeal membrane oxygenation
JIAN Meng1, ZHANG Mingkui2,3, HUANG Jianbing4, LUO Xianwu1,3
1. Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China; 2. First Hospital of Tsinghua University, Beijing 100016, China; 3. Cardiovascular Tissue Engineering and Biomaterials Laboratory, School of Clinical Medicine, Tsinghua University, Beijing 100084, China; 4. Guangzhou Laboratory, Guangzhou 510005, China
Abstract：Objective］ Extracorporeal membrane oxygenation (ECMO) is an effective life support treatment for severe cardiopulmonary failure and is widely used as supportive therapy for COVID-19. The design and assessment of ECMO oxygenators, which consist of thousands of 3D hollow fiber bundles, are essential to expanding their clinical applications. This study aims to investigate the effects of 3D fiber membrane array structure on the hemodynamic loss and gas transfer efficiency in ECMO. An axial slice of a commercial oxygenator is selected as a simplified model. ［Methods］ The immersed boundary (IB) method code was developed to simulate the two-dimensional steady laminar flow, and a segregated solver was implemented during the coupled multi-component gas transfer in ECMO. A grid independence test was carried out to ensure that the computational results were not influenced by the grid size. Results obtained from the IB method, commercial computational fluid dynamics (CFD) software Fluent with a body-fitted mesh, and the reference showed a good agreement, validating the accuracy of the IB method and the gas transfer solver. Seven array arrangement schemes with constant porosity were simulated at Re=5, and the results of permeance, wall shear stress, vortex distribution, and entropy generation rate were compared. ［Results］ Numerical results showed that when porosity was constant, different fiber array arrangements and angles between the odd and even row fibers could significantly change the flow state and gas transfer performance by affecting the relative value of axial and radial permeability. Inline arrangements and small angles between the odd and even row fiber arrangements deteriorated the uniformity of the flow state, consequently enlarging flow separation zones and causing peak wall shear stress. The array staggering from the axial direction and large angles between the odd and even rows could be used to avoid the large-scale vortex at the outlet of the ECMO and reduce the risk of blood damage. For all fiber array configurations, the head loss values predicted by entropy generation theory were smaller than the calculated results. As for gas transfer, in regions near the oxygenator inlet, outlet, and fluid retention zones, gas was mainly transferred through diffusion, controlled by the concentration gradient. In the middle stream regions, convection dominated the gas transfer. Further analysis showed that the gas transfer performance was mainly affected by the array arrangement. Compared with inline arrays, staggered arrangements increased the gas transfer rate on the upstream side and gaps of adjacent fibers. For the staggered arrangement where the flow passage had no evident periodic contraction and expansion, the flow retention area was small. Thus, the effective oxygenation area was the largest, and the gas was transported mainly by convection, which resulted in a high gas transfer rate. In addition, the gas transfer efficiency improved by increasing the angle between the odd and even rows. ［Conclusions］ The simulated pressure drop results of the simplified model are within the clinical operating range, but its gas transfer rate is lower than that of commercial oxygenators. Our results can serve as a reference for further 3D pore-scale numerical simulation and as a scientific basis for the structural optimization and clinical applications of ECMO.
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2023, Vol. 63 
