The friction characteristics of a mechanical seal for rotary blood pumps were investigated to evaluate the volume percentage of blood in the sealing face. These mechanical seals separate blood and cooling water, so the fluid film in the sealing face is composed of two different solutions. Therefore, the volume percentage of each solution is not known. In the experiments, various viscosities of an ethylene glycol solution were used as a substitution for blood, and the friction characteristics were compared for different Ra values for the seat rings: 0.009 and 0.088 μm. These friction characteristics were investigated based on the two different assumptions: a completely mixed state and a completely separated state. As a result, the volume percentage of the sealed fluid in the completely mixed state was larger than that in the completely separated state. In fact, it was considered reasonable that the practical state in the sealing face was between two states. For example, the volume percentage of the sealed fluid showed 65-73% at a viscosity of the sealed fluid of 3.53 mPa·s and at a rotational speed of 3000 min-1. Additionally, it was found that smaller volume percentage of the sealed fluid was evaluated for 0.088 μmRa than for 0.009 μmRa.
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