Résumé
Objective To investigate the effects of particle size, wind speed and dumping velocity on aerosol concentration distribution during powder dumping in a reprocessing plant. Methods CeO2 powder was selected as the substitute material of PuO2. FLUENT software was used to calculate the pouring process of CeO2 powder under different operation conditions. Then the aerosol concentration distribution under different dumping speeds was measured by particle size spectrometer to verify the accuracy of simulation results. Results The particles with small particle size are more likely to be separated from the mainstream area by the drag force of the surrounding gas, and the radius of the diffusion range also increases with the decrease of the particle size. 2) When the ventilation speed is less than 1 m/s, the dust lifting can be reduced and the concentration of dust particles in the chamber can be reduced to a certain extent. 3) In the process of powder dumping, the spoon is rotated anticlockwise at a speed of 100° in 2～3 s, and less dust aerosol is produced on the right side of the tray. Conclusion When operating the powder particles with smaller particle size, more attention should be paid to the monitoring of aerosol at different positions; the change of air inlet velocity makes the flow field in glove box more complex, and the volume fraction of dust particles is related to the size and location of vortex formed by airflow. The greater the wind speed, the greater the impact on the powder dumping process. The experimental results are basically consistent with the simulation results, and the results show that the lower the dumping speed, the smaller the aerosol concentration near the tray.
Résumé
Objective To study movement process of circulating tumor cells (CTCs) in the blood and mechanism of CTC capture by CellCollector, and reveal relationship between the detected CTC numbers and the actual CTC concentration in the body. Methods Based on Fluent and EDEM software, the unidirectional fluid-solid interaction method was applied to establish a two-phase flow model, including the hemodynamic model and the CTC transport model, and capture simulations under different CTC concentration conditions were conducted. Results The number of CTCs captured by CellCollector was significantly positively correlated with the CTC concentration in the body. When the CTC concentration was low, CTCs could only be captured in several time intervals, and the capture had a certain contingency; as the concentration increased, the uniformity of CTC capture over time became better, and the total number of captures also increased. Conclusions Through the fitting of simulation results, analytical quantitative relationship between the captured CTC number and the CTC concentration in the body is preliminarily given, which provides theoretical basis and mechanical explanation for the clinical use of CellCollector.
Résumé
Objective To study the two-phase flow dynamics distribution and red blood cell distribution under the fluid-solid coupling interaction in left coronary artery at the typical time point within one cardiac cycle,and to investigate the formation and development mechanisms of left coronary artery atherosclerotic plaque Methods The blood was regarded as a two-phase fluid.Based on fluid-solid interaction between blood and vascular wall,the computational fluid dynamics method was used to make the transient numerical simulation of two-phase flow in the left coronary artery under fluid-solid interaction;the distribution of blood flow in the left coronary artery at the typical time point within one cardiac cycle was studied,the relationship between hemodynamic parameters and the formation of atherosclerotic plaque was analyzed.Results A lowspeed eddy zone existed in an area between the distal segment of circumferential branch and the proximal outside of blunt-edge branch of the left coronary artery,where both internal wall shear stress and red blood cell volume fraction were very small and the blood flow pattern was very complicated.Conclusion At the lowspeed eddy zone that carries small wall shear stress,the lipid concentration polarization and macromolecular material deposition are easy to be produced.The area that has less red blood cells is liable to develop hypoxia,resulting in increased vascular wall permeability and intimal injury,which will activate the immune system,causing lipid accumulation in vascular wall and intimal hyperplasia and,thus,to induce the formation of atherosclerotic plaque.(J Intervent Radiol,2017,26:253-257)