CFD simulation is performed for the purpose of making one-dimensional model of flow with low velocity in a complicated-shape of microscopic lymphatic vessel. The vessel is supposed to be axially symmetric on the basis of visualized shape of the vessel. It is composed of eight-staged conical parts connected, in which there are seven tapered valves at equal distance. To assure the accuracy of the simulation, the well-known Hagen-Poiseuille flow is first analyzed, by which the friction loss, i.e.,

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... the pressure loss due to viscosity at the wall, and the friction coefficient are correctly recovered. The simulation analysis of three-dimensional flow in the vessel clarifies the flow field, the pressure distribution longitudinal to the vessel, the friction losses for all conical parts, and the pressure loss coefficient at the exit of the valve. The friction coefficients for all the conical parts are formulated on the basis of the friction losses on the assumption of one-dimensional flow in the vessel. The friction coefficients and the pressure loss coefficient are found to be in inversely proportional to Reynolds numbers, and also the pressure distribution along the vessel is accurately reconstructed by one-dimensional model. In particular, the friction coefficient is different from the Hagen-Poiseuille formula.