The benefit of using FEMLAB 3.1 as a tool in teaching biomechanics and biomedical physics at Uppsala UniversityJesper Gantelius
The alveolus is the smallest functional unit of the lung, and is the only region where oxygen from the air enters the bloodstream, as well as where carbon dioxide is vented out. There are approximately six hundred million alveoli in the lungs of every human, and the branched lungs seem to mimic a fractal surface to provide a total area of exchange of more than a hundred square meters. The alveolar sacs are connected to small air ducts, bronchioles, which in turn continue to merge into larger and larger structures that ultimately form the lobes of the two lungs. Air is inhaled and exhaled through the decrease and increase of air pressure in the lungs that result from the tension and relaxation of the diaphragm.
In this model, four micro capillaries each with a constant inner radius of 5 micrometer travel halfway around the alveolus. The flow field is simulated using the Navier Stokes equations, with an inflow velocity of 1 mm/s, with no-slip conditions at the capillary walls, and pressure=0 as the outflow boundary condition. The blood is approximated as a water-like fluid with a density of 1000 kg/m3 and a dynamic viscosity of 10-3 Pa*s.