RESUMO
This study utilises computational fluid dynamics simulations with the OpenFOAM computational framework to investigate and compare the in-plane and through-plane permeability properties of four different gas diffusion layers (GDLs). Also the through-plane water and air relative permeability values and water saturations at different rates were simulated. Permeability analysis enhances our understanding of fluid flow, ways to decrease pressure loss in the GDL, and methods to enhance oxygen concentration at the catalyst layer interface through convection. The analysis reveals that the investigated GDL materials have spatial heterogeneity of porosity and permeability, especially in the Sigracet SGL 25 BA GDL. However, the porosity and permeability of the Toray TGP-H 060 and AvCarb 370 MGL GDLs exhibit less variations. The two-phase flow studies on GDL saturation show that at the same water injection flowrate, the AvCarb 370 MGL GDL has the largest remaining water saturation, with Sigracet SGL 25 BA GDL being the less saturated GDL among the four investigated GDLs. The compression from the ribs significantly affected the in-plane permeabilities of both Toray TGP-H 060 and especially impacted Sigracet SGL 25 BA GDL. This impact was expected as the pore size distribution varied significantly in the areas under the ribs versus the channel.
RESUMO
This paper presents a novel two-dimensional (2D) computational modeling of the retinal oxygen delivery, transport, and consumption analysis. The 2D modeling allows the division of the retina into four layers to address different flow profiles. The retina domain was meshed using the ICEM CFD mesher, while the ANSYS Fluent was used to calculate the transport phenomena for the four different layers. Clinical cases such as diabetes and sickle cell anaemia denoting the effects of decreasing retinal blood flow and hemoglobin's oxygen affinity were investigated. The simulation results showed that for a healthy retina in light and dark conditions, the outer retina is in danger of hypoxia at thickness >197.56µm. However, the treatment of severe ischaemia using extreme hyperoxia seems beneficial for retinal thickness >197.56µm but harmful for thickness <122.75µm. The reduction of hemoglobin's oxygen affinity at low blood flow regimes could not improve the retina's oxygen levels. The study supports the oxygen toxicity hypothesis that hypoxia causes retina degeneration and estimates the retinal thickness and lighting conditions (dark or light) this may occur.