Iranian Journal of Chemical Engineering (IJChE)

Abstract The impact of bed loading on minimum spouting velocity (ums) of polydispersed TiO2 particles was studied in a conical fluidized bed. The experiments were performed at different bed loadings according to Gaussian and narrow-cut particle size distribution (PSD). The bed consisted of simple-agglomerates in size range of 30-90 µm belonging to Geldarts’ group A classification. The effect of PSD and interparticle force (IPF) on the predicted ums and hysteresis in the pressure profiles were studied through a combination of computational fluid dynamics and discrete element method (CFD-DEM). The experimental data showed that the choice of bed with Gaussian PSD-type led to more accurately predicting ums than the narrow-cut particle PSD. The impact of IPF on the expected ums became more critical than the PSD type because of an increase in bed loadings. The lowest deviations the results were obtained in the low bed loadings, which is confirmed the accuracy of simulation results. The simultaneous effects of PSD-type and IPF led to a change in the fluidization behavior of the bed. The bed with narrow-cut PSD has a hydrodynamic behavior similar to spouting and slugging regimes, while the fluidization quality of the bed improves by fine particles.

Abstract The size and lifetime of evaporating sneeze droplets in the indoor environment were studied experimentally and theoretically. The effects of indoor temperature T_∞ and indoor humidity RH_∞ on evaporating droplets with the initial diameters of 4.9, 8.1, 17.2, and 29.7 μm were investigated. The size distribution and mean size of droplets were obtained by a laser particle sizer. The experimental data showed that the possibility of aerosolized droplets increased from 25.5 to 36.1 % by increasing T_∞ from 18 to 30 °C and decreased from 36.1 to 13.6 % by increasing RH_∞ from 30 to 60 %. A one-dimensional droplet evaporation model was used to estimate the lifetime of the droplet. A critical RH_∞ of 40 % was found; above it, the lifetime of the droplet exponentially increases. The effect of the initial diameter of droplets was higher than that of RH_∞ and also the impact of RH_∞ was higher than that of T_∞ on the lifetime of the aerosolized droplet nuclei. A significant effect of environmental conditions on the lifetime of the droplet was found over the range of 26 °C ≤ T_∞ ≤ 30 °C and RH_∞ ≤ 40 %, while the effect decreased in the range of 18 °C ≤ T_∞ ≤ 22 °C and RH_∞ > 40 %, where a minimal shrinkage of droplets took place because of the hygroscopic growth of droplets. The results of this study do not imply that the COVID-19 virus will be deactivated at the end of the lifetime of the droplet, but it represents that controlling the indoor environment is important for droplets to carry the virus.

Abstract In this study, the inactivation performance of units against pathogenic and biotoxin threats in a water treatment plant is studied. The assessment of the units and hazards of the water treatment plant against each of threats is studied by the RAMCAP risk analysis. The experiments showed that the Aflatoxin was eliminated only by disinfection units. The reverse osmosis unit had high efficiency in removing Ricin, while the sand filtration had the lowest efficiency in removing biotoxins. The microbial analysis showed the total coliform bacteria, thermotolerant coliform and HPC index were increased slightly by increasing the incoming water's pH and turbidity, while their count were significantly reduced by increasing the free residual chlorine. Changes in the water temperature also had minor effects on microbial indexes. The RAMCAP analysis is used to reduce the vulnerability of units to conventional threats by determining