This paper discusses the straight-through type labyrinth seal. This labyrinth seal is used for axial flow fans, which have an outer ring at the blade tip to seal the clearance between the ring tip and the fan shroud, in order to prevent the reverse flow or leakage. These fans are used for the cooling of automobile radiators. In these cases, the labyrinth seal is used in an extremely low static pressure difference and a large clearance. A significant decrease of the leakage rate was reported even when the labyrinth seal rotated in comparatively low speed in this unique condition according to the authors' former report. However, this phenomenon is different from past research. Furthermore the cause of this phenomenon has not been determined. Therefore, the internal flow was depicted with Computational Fluid Dynamics (CFD) in order to clarify the cause of this phenomenon. The results of CFD show that the leakage rate decreases significantly because the carry-over flow is intercepted in the expansion groove. This is the newly discovered phenomenon which occurs under the unique condition of an extremely low differential pressure. It has not been pointed out before as the reason why the rotation decreases the leakage rate.

Many studies have been conducted on ventilator-associated complications (VACs) in COVID-19 patients. However, in these studies, the causative organisms were similar, and there are no reports on VAC corresponding with Corynebacteria. Coryneforms are frequently cultured in polymicrobial infections and are usually considered contaminants in respiratory specimens. However today, Corynebacterium pseudodiphtheriticum or striatum is known to be a pathogen in lower respiratory tract infection. We report three cases of VAC probably due to Corynebacterium pseudodiphtheriticum in COVID-19 patients. If purulent lower respiratory specimens showed coryneform predominantly via Gram staining, empirical therapy should be started. Furthermore, species identification and drug susceptibility testing should be performed.

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Abs ractG : The low pressure axial flow fans with an outer ring, used for cooling automobile radiators, have a significantly large tip clearance between the ring tip and the fan shroud. It has been found that the turbulent reverse flow, or leakage flow, which occurs at the tip clearance, greatly affects the fan performance and noise level. Therefore, in order to improve the fan performance and noise level it is important to decrease the effect of leakage at the tip clearance. The authors investigated the performance of the straight-through type of labyrinth seal which operates in an extremely low static pressure difference with a large clearance. It was hoped that by sealing this clearance with the labyrinth seal the performance would be improved. It was verified that the labyrinth seal satisfied almost the same performance as that predicted by the previous theory. This theory was established by experimental studies in the condition of quite high static pressure difference when the labyrinth is stationary. However, it was later discovered that the leakage rate decreased significantly even though there was far lower ring speed in comparison to past research results where the ring rotated. This phenomenon is conspicuous in a lower differential pressure. However, the cause of this phenomenon has not been determined. t t