No abstract

No abstract

No abstract

Based on the Maxwell's equations and low‐Reynolds number k−ϵ turbulence model, a coupled three‐dimensional numerical model has been developed to describe the electromagnetic field, fluid flow, and solidification in a bloom continuous casting mold with electromagnetic stirring (M‐EMS). The optimum frequency is obtained by calculating the maximum electromagnetic torque of the strand with consideration of mold tube shield effect. The effect of stirring current intensity on the turbulent flow, temperature distribution, and shell growth has been investigated numerically. According to the simulation results, the electromagnetic force with a circumferential distribution on the strand transverse section, and a swirling flow field along the axial direction of the strand are observed in the mold region with the application of M‐EMS. It is shown that the melt maximum swirling flow velocity decreases from 0.420 to 0.226 m s−1 and the flow field changes remarkably when solidification is involved in the model. With the current intensity increasing from 260 to 500 A, the swirling flow intensifies significantly, which prevents the superheated molten steel moving downwards to the liquid core and promotes the superheat dissipation in mold.

No abstract

Aerosol samples of PM and PM were collected every 6 days from March 2012 to February 2013 in Huangshi, a typical industrial city in central China, to investigate the characteristics, relationships, and sources of carbonaceous species. The PM and PM samples were analyzed for organic carbon (OC), elemental carbon (EC), char, and soot using the thermal/optical reflectance (TOR) method following the IMPROVE_A protocol. PM and PM concentrations ranged from 29.37 to 501.43 μg m and from 50.42 to 330.07 μg m, with average levels of 104.90 and 151.23 μg m, respectively. The 24-h average level of PM was about three times the US EPA standard of 35 μg m, and significantly exceeds the Class II National Air Quality Standard of China of 75 μg m. The seasonal cycles of PM mass and OC concentrations were higher during winter than in summer. EC and char concentrations were generally highest during winter but lowest in spring, while higher soot concentrations occurred in summer. This seasonal variation could be attributed to different seasonal meteorological conditions and changes in source contributions. Strong correlations between OC and EC were found for both PM and PM in winter and fall, while char and soot showed a moderate correlation in summer and winter. The average OC/EC ratios were 5.11 and 4.46 for PM and PM, respectively, with individual OC/EC ratios nearly always exceeding 2.0. Higher char/soot ratios during the four seasons indicated that coal combustion and biomass burning were the major sources for carbonaceous aerosol in Huangshi. Contrary to expectations, secondary organic carbon (SOC) which is estimated using the EC tracer method exhibited spring maximum and summer minimum, suggesting that photochemical activity is not a leading factor in the formation of secondary organic aerosols in the study area. The contribution of SOC to OC concentration for PM and PM were 47.33 and 45.38%, respectively, implying that SOC was an important component of OC mass. The serious air pollution in haze-fog episode was strongly correlated with the emissions of pollutants from biomass burning and the meteorological conditions.

No abstract

No abstract