Abstract
The efficiency of axial dispersion of respiratory gases is improved by manipulating the flow wave form of oscillatory flow, e. g., the intermittent oscillatory flow, contributing to the advancement of ventilation by high-frequency oscillation (HFO). The purpose of this study was to investigate experimentally the effect of intermittent oscillatory flow on axial dispersion. An electromagnetic vibrator was installed at one end of a straight tube, via the bell mouth, with the inner diameter of 15. 6 mm and the total length of 4 m. Velocity was measured by a hot-film anemometer, and the concentration of carbon dioxide was measured by an infrared absorption CO2 sensor. The effective diffusivity is dependent on the flow patterns, and the effective diffusivity increased significantly upon increasing the duration of stationary phase, with the maximum ratio of effective diffusivity to the molecular diffusivity double the that of sinusoidal oscillatory flow. Moreover, turbulence appears in the decelerating and stationary phase at high Reynolds numbers. In that case, the augmentation reached more than threefold. These results encourage effective use of intermittent oscillatory flow for ventilation by HFO.
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