Transport and flow characteristics of an oscillating cylindrical fiber for total artificial lung application

Mass transport and fluid dynamics characteristics in the vicinity of an oscillating cylindrical fiber with an imposed pulsatile inflow condition are computationally investigated in the present study. The work is motivated by a recently proposed design modification to the Total Artificial Lung (TAL) device, which is expected to provide better gas exchange. Navier–Stokes computations, coupled with convection–diffusion equation are performed to assess flow dynamics and mass transport behavior around the oscillating fiber. The oscillations and the pulsatile free stream velocity are represented by two sinusoidal functions. The resulting non-dimensional parameters are Keulegan–Carpenter number (KC), Schmidt number (Sc), Reynolds number (Re), pulsatile inflow amplitude (ΔU∞∗$ \Delta U^*_\infty $), and amplitude of cylinder oscillation (A∗$ A^* $). Results are computed for 0.14≤KC≤1$ 0.14 \le \mathrm{KC} \le 1 $, Sc = 1000, Re = 5 and 10, ΔU∞∗=0.4$ \Delta U^*_\infty =0.4 $ and 0.7 and 0.25 ≤$ \le $A∗$ A^* $≤$ \le $ 5.25. The pulsatile inflow parameters correspond to the flow velocities found in human pulmonary artery while matching the operating TAL Reynolds number. Mass transport from the surface of the cylinder to the bulk fluid is found to be primarily dependent on the size of surface vortices created by the movement of the cylinder. Time-averaged surface Sherwood number (Sh) is dependent on the amplitude and KC of cylinder oscillation. Compared to the fixed cylinder case, a significant gain up to 380% in Sh is achieved by oscillating the cylinder even at the small displacement amplitude (AD = 0.75D). Moreover, with decrease in KC the oscillating cylinder exhibits a lower drag amplitude compared with the fixed cylinder case. Inflow pulsation amplitude has minor effects on the mass transport characteristics. However, an increase in ΔU∞∗$ \Delta U^*_\infty $ results in an increase in the amplitude of the periodic drag force on the cylinder. This rise in the drag amplitude is similar to that measured for the fixed cylinder case. Quantifications of shear stress distribution in the bulk fluid suggest that the physiological concerns of platelet activation and injury to red blood cells due to cylinder oscillation are negligible.