This paper studies the spatial concentration distribution and temporal evolution of exhaled and sneezed/coughed droplets within the range of 1.0 to 10.0 μm in an office room with three air distribution methods,includ...This paper studies the spatial concentration distribution and temporal evolution of exhaled and sneezed/coughed droplets within the range of 1.0 to 10.0 μm in an office room with three air distribution methods,including mixing ventilation（MV）,displacement ventilation（DV）,and under-floor air distribution（UFAD）.The simulation results indicate that exhaled droplets with diameters up to 10.0 μm from normal respiration process are uniformly distributed in MV.However,they become trapped at the breathing height by thermal stratifications in DV and UFAD,resulting in a high droplet concentration and an increased exposure risk to other occupants.Sneezed/coughed droplets are more slowly diluted in DV/UFAD than in MV.Low air speed in the breathing zone in DV/UFAD can lead to prolonged human exposure to droplets in the breathing zone.展开更多
Taking Adaohai Coal Mine as the example, underground pressure appearance laws of fully mechanized top coal slice caving on high-dipping and thick coal seams. Through site visit, theoretical analysis and discrete eleme...Taking Adaohai Coal Mine as the example, underground pressure appearance laws of fully mechanized top coal slice caving on high-dipping and thick coal seams. Through site visit, theoretical analysis and discrete element calculation, the research shows that, as the mining deepens, underground stress of lower sublevels is more obvious and higher than that of upper sublevels and is higher in the air return roadway than that in the air intake roadway in the area that is near to the top coal. Because the top coal is thick and gangue is caved above the support, underground pressure to the working face is relatively gentle. Immediate roof will mainly fall down along the floor. Main roof and the rock bed above the main roof will move to the mined out area along the fault in the early stage and then fall down with the mined out area later. In addition, roof pressure mainly periodically appears in two directions along the trend and the dip.展开更多
基金The National Natural Science Foundation of China(No.50808133)the Dean's Reserve of Faculty of Construction and Land Use at the Hong Kong Polytechnic University
文摘This paper studies the spatial concentration distribution and temporal evolution of exhaled and sneezed/coughed droplets within the range of 1.0 to 10.0 μm in an office room with three air distribution methods,including mixing ventilation（MV）,displacement ventilation（DV）,and under-floor air distribution（UFAD）.The simulation results indicate that exhaled droplets with diameters up to 10.0 μm from normal respiration process are uniformly distributed in MV.However,they become trapped at the breathing height by thermal stratifications in DV and UFAD,resulting in a high droplet concentration and an increased exposure risk to other occupants.Sneezed/coughed droplets are more slowly diluted in DV/UFAD than in MV.Low air speed in the breathing zone in DV/UFAD can lead to prolonged human exposure to droplets in the breathing zone.
基金Supported by the Scientific Research Business of China University of Mining ＆ Technology （Beijing） （2009QZ04） the National Natural Science Foundation of China （50974123）
文摘Taking Adaohai Coal Mine as the example, underground pressure appearance laws of fully mechanized top coal slice caving on high-dipping and thick coal seams. Through site visit, theoretical analysis and discrete element calculation, the research shows that, as the mining deepens, underground stress of lower sublevels is more obvious and higher than that of upper sublevels and is higher in the air return roadway than that in the air intake roadway in the area that is near to the top coal. Because the top coal is thick and gangue is caved above the support, underground pressure to the working face is relatively gentle. Immediate roof will mainly fall down along the floor. Main roof and the rock bed above the main roof will move to the mined out area along the fault in the early stage and then fall down with the mined out area later. In addition, roof pressure mainly periodically appears in two directions along the trend and the dip.
