A flow analysis around a face shield was performed to examine the risk of virus infection when a medical worker wearing a face shield is exposed to a patient’s sneeze from the front. We ensured a space between the shield surface and the face of the human model to imitate the most popularly used face shields. In the present simulation, a large eddy simulation was conducted to simulate the vortex structure generated by the sneezing flow near the face shield. It was confirmed that the airflow in the space between the face shield and the face was observed to vary with human respiration. The high-velocity flow created by sneezing or coughing generates vortex ring structures, which gradually become unstable and deform in three dimensions. Vortex rings reach the top and bottom edges of the shield and form a high-velocity entrainment flow. It is suggested that vortex rings capture small-sized particles, i.e., sneezing droplets and aerosols, and transport them to the top and bottom edges of the face shield because vortex rings have the ability to transport microparticles. It was also confirmed that some particles (in this simulation, 4.4% of the released droplets) entered the inside of the face shield and reached the vicinity of the nose. This indicates that a medical worker wearing a face shield may inhale the transported droplets or aerosol if the time when the vortex rings reach the face shield is synchronized with the inhalation period of breathing.

In this study, a new upgrading method with supercritical water was developed for heavy oil in order to produce light oil that was free from heavy metal and heavy hydrocarbon fraction under coke suppression condition. Heating experiments of the heavy oil with and without supercritical water were conducted to gain insights into temporal variation of gas, maltene, asphaltene, and coke yield and existence state of heavy metal vanadium in the heavy oil. The experiments were carried out by an autoclave apparatus with and without continuous supply of supercritical water at 25 MPa and from 400 to 470℃. Results of the experiments showed that gas and reformed oil that composed of maltene was selectively extracted by supercritical water and its extraction rate was increased proportional to temperature. It was valid for suppressing coke formation to heat the heavy oil within coke induction period. The vanadium should be enriched into heavy fraction, because concentration of vanadium in residual oil was proportional to asphaltene concentration. Based on these experimental results, a new upgrading method that works out without detriment to extraction rate of gas and reformed oil under coke suppressing condition was designed. This method was followed by heating the heavy oil at 450℃ within coke induction period and extraction of gas and reformed oil at 400℃ by supercritical water. We have confirmed that this upgrading method enabled us to depress the coke yield 1/70 fewer than 450℃ on extraction rate at 450℃.

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