Many years ago I helped to support an experiment conducted in Japan which investigated the effects of high frequency oscillation ventilation (HFOV) on the mixing and distribution of gas into the lungs.
But this experiment rather simplified the system by using a simple horizontal tube, perhaps 2 meters in length. At one end of the tube a plenum was placed, and at the other, an HFOV ventilator. Initially the system was filled with air. An oxygen cell was placed in the plenum to measure the $O_2$ concentration. At the start of each experiment, a small volume (maybe 500 mL) of pure oxygen was introduced slowly at the end where the HFOV ventilator was attached.
Although I can't recall all the details of the experiment, I do remember one result that's left me baffled all these years. The following two experiments:
(1) After introducing the oxygen the system was left unpowered so that natural diffusion would occur. (2) After introducing the oxygen, the HFOV ventilator was turned on and allowed to oscillate the gas column
Note that oscillating the gas column with the ventilator results in no net displacement of the gas. Perhaps only 100 mL back and forth displacement. And the volume of the full tube is significantly larger than the volume of the introduced oxygen.The HFOV machine was able to oscillate at frequencies between 4 and 20 Hz.
The expected result would be that the oscillations would promote the movement of the oxygen towards the plenum. But the opposite, confounding result occurred. The oscillations actually inhibited the movement of the oxygen by a significant time.
I'm guessing now but diffusion maybe took an hour without oscillation. But with oscillation it took maybe 30 minutes longer.
So my question: are there any known physical properties of oscillating flow that could explain such a result?
I tried researching to see if the work was ever published, but no luck. The physician I worked with was a Dr. Miao.
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