Flow partitioning in symmetric cascades of branches

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Abstract
Markedly nonuniform partitioning of flow was found in idealized [human] models of physiological cascades of branches. Liquids having viscosities of 0.8-7.0 cP [Pascal] were used to investigate this effect systematically in a regime characterizing a limited range of pulmonary flows, comprising inlet flow rates of 500-3000 ml/min and branch diameters of 1.0 cm ID [internal diameter]. Factors that affect the nonuniformity of inspiratory flow include inlet velocity profile and flow rate, cascade aspect (L/D) ratio, exit pressure distribution, and, to a lesser extent, kinematic viscosity (.mu./.rho.). More qualitative observations using sinusoidally oscillating airflow revealed inspiratory and expiratory flow patterns to be quite dissimilar, emphasizing the inadequacy of a resistance model of flow partitioning based on Kirchhoff''s law. Results might suggest why regional ventilation in man is flow- or frequency-dependent and how bronchial smooth muscle could fine-tune regional ventilation.

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