| The focus of this study is an experimental apparatus that serves as a model for studying blood flow in a total artificial lung (TAL), a prototype device intended to serves as a bridge to lung transplantation or that supports pulmonary function during the treatment of severe respiratory failure. The TAL consists of hollow cylindrical fibers that oxygen-rich air flows through and oxygen-poor blood flows around. Since gas diffusivity in the TAL is very small, a convection mechanism dominates the gas transport, which is why we focus on the velocity around the fibers (modeled as a 0.05-cm-in-diameter and 5-cm-long cylinder). We designed a low-speed water tunnel to study the flow mechanism around the cylinder, across which the flow is generated by a linear actuator that allows different flow patterns to mimic the flow in a TAL. Knowledge gained from the flow around cylinders is beneficial for understanding flow patterns around fibers in TALs. We present summary of vortex formation behind a cylinder for Reynolds numbers (Re) of 1-5 and Stokes numbers (Ns) of 0.18-0.37; results show that higher Re and Ns favor vortex formation, and vortices were observed in low Reynolds numbers where no vortex was formed in steady flow. The vortex structures behind two cylinders with different configurations were also investigated using PIV method and compared with numerical results. It is shown that the arrangement of the cylinders plays an important role in the vortex structures behind the cylinders. These findings regarding the parameter range for vortex formation and effects of fibers' configurations may provide principles for designing artificial lungs to enhance convective mixing. We anticipate that the pulsatile flow circuit presented here can be used to mimic the flow not only in TALs but in other physiological systems. |
