A three-dimensional computational fluid dynamics (CFD) model of a Roots blower with a backflow design was established to analyse the effects of the backflow on the Roots blower's performance. A prototype of Roots blower with a backflow design was manufactured to validate the CFD model through the pressure distribution and the mass flow rate. The results showed that the proposed CFD model agreed well with the experimental data. The effects of the sizes and directions of the backflow passage on the Roots blower's performance were then investigated using the validated CFD model. It was found that under a properly sized backflow passage, the pressure pulsation and the shaft power can be decreased by 80% and13%, respectively; However, the mass flow rate was reduced by 12% under the same size of backflow passage. Although the direction of the backflow passage affected the shaft power, it had no effect on the mass flow rate or pressure pulsation. The shaft power consumption of a Roots blower with a vertical backflow was 4% lower than a horizontal backflow.
BACKGROUND
Complicated crown-root fracture is considered a severe dental trauma and is unlikely to heal without treatment. Usually, dentists have to remove the loose coronal fragment of the fractured tooth and treat the remaining part with multidisciplinary approaches. However, we observed spontaneous healing of fracture in two pediatric cases with a history of complicated crown-root fractures over 4 years ago.
CASE SUMMARY
In case 1, a 12-year-old boy complained of pain at tooth 11 following an accidental fall 1 d ago. Clinical examination showed a crack line on the crown of tooth 11. Cone beam computed tomography (CBCT) images of tooth 11 showed signs of hard tissue deposition between the fractured fragments. The patient recalled that tooth 11 had struck the floor 1 year ago without seeking any other treatment. In case 2, a 10-year-old girl fell down 1 d ago and wanted to have her teeth examined. Clinical examination showed a fracture line on the crown of tooth 21. CBCT images of tooth 21 also showed signs of hard tissue deposition between the fractured fragments. She also had a history of dental trauma 1 year ago and her tooth 11 received dental treatment by another dentist. According to her periapical radiograph at that time, tooth 21 was fractured 1 year ago and the fracture was overlooked by her dentist. Both of these two cases showed spontaneous healing of complicated crown-root fractures. After over 4 years of follow-up, both fractured teeth showed no signs of abnormality.
CONCLUSION
These findings may provide new insights and perspectives on the management and treatment of crown-root fractures in children.
Ozone advanced oxidation has been widely used in water treatment, but little research has been reported on the application of ozone to difficult-to-degrade mineral wastewater. In this paper, the effect of ozonation application in the treatment of copper mineral processing wastewater, which is difficult to be effectively treated by traditional processes due to its complex composition, was investigated. The effects of ozonation time, ozone concentration, temperature and pH on the degradation of organic compounds in the wastewater by ozonation were researched. It was found that the chemical oxygen demand (COD) of the wastewater could be reduced by 83.02% by ozonation under optimal treatment conditions. In addition, the mechanism of ozone degradation of the difficult-to-degrade wastewater was studied, and the reasons for the fluctuating variations of COD and ammonia nitrogen during ozonation treatment were explained.
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