| Budget Amount *help |
¥13,600,000 (Direct Cost: ¥13,600,000)
Fiscal Year 2002: ¥3,900,000 (Direct Cost: ¥3,900,000)
Fiscal Year 2001: ¥9,700,000 (Direct Cost: ¥9,700,000)
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| Research Abstract |
The airway of the human lung consists of a very complicated branching tube network. At each bronchus, the airways repeat branching with their average diameter and the length decreasing. At the end of airways, numerous alveoli that exchange carbon dioxide for oxygen exist. As for the gas transport in the conducting airways, a lot of researches have been done. However, the mechanism how the fresh air, which was inhaled in the inspiration process, reaches alveoli is not known well yet. Recently, the authors revealed that bi-directional axial gas-exchange phenomenon occurring in the conducting airways of human lung system was governed by "trap-and-release" mechanism caused by "generation-and-extinction" of flow-separation regions.
In order to further examine the phenomena occurring in the real human lung, three-dimensional test sections were newly constructed in addition to the two-dimensional one. Flow visualization experiments and numerical analysis in reciprocating flow inside a multi-ge
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neration branching-tube network were performed. In the experiments, the followings were revealed : (1) Even in the 3-D test section, "trap-and-release" mechanism played an important role. (2) In the 3-D test section, asymmetric flow in the ancestor tube results in the different axial mass transport speed depending on the path. (3) The fastest path concerning the axial mass transport changed depending on the geometric configuration decided by the rotation angle between the successive branches.
In the numerical analysis, the finite volume method was used, and a two-dimensional branching case was computed with three different branching angles. In the numerical results, the relation between the size of the flow-separation bubble and axial mass transport was observed. The relation was not monotonic, and therefore there must be an optimal branching angle. By examining the flow field in detail, it was observed that the flow-separation bubble had two effects on the mass transport enhancement : the "trap-and-release" effect and the acceleration of the fluid bv reducing the cross-sectional area of the flow passaee. Less
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