Gas flow characteristics in nanopores were investigated experimentally and numerically using molecular dynamics (MD) simulations with an emphasis on the friction factor and gas viscosity. The results show that the vis...Gas flow characteristics in nanopores were investigated experimentally and numerically using molecular dynamics (MD) simulations with an emphasis on the friction factor and gas viscosity. The results show that the viscosity and the friction factor in nanopores are much lower than those in macroscale channels. The actual viscosities obtained from the MD studies showed that the gas viscosity in nanopores is less than the macroscale viscosity because collisions between gas molecules are less frequent in high Knudsen number flows and there are more collisions with the wall. The MD simulations show that the velocity profile is composed of two parts, with a much steeper velocity gradient near the wall.展开更多
Gate valve has various placements in the practical usages.Due to the effect of gravity,particle trajectories and erosions are distinct between placements.Thus in this study,gas-solid flow properties and erosion in gat...Gate valve has various placements in the practical usages.Due to the effect of gravity,particle trajectories and erosions are distinct between placements.Thus in this study,gas-solid flow properties and erosion in gate valve for horizontal placement and vertical placement are discussed and compared by using Euler-Lagrange simulation method.The structure of a gate valve and a simplified structure are investigated.The simulation procedure is validated in our published paper by comparing with the experiment data of a pipe and an elbow.The results show that for all investigated open degrees and Stokes numbers(St),there are little difference of gas flow properties and flow coefficients between two placements.It is also found that the trajectories of particles for two placements are mostly identical when St << 1,making the erosion independent of placement.With the increase of St,the distinction of trajectories between placements becomes more obvious,leading to an increasing difference of the erosion distributions.Besides,the total erosion ratio of surface T for horizontal placement is two orders of magnitudes larger than that for vertical placement when the particle diameter is 250 μm.展开更多
Entrance region may have important effect on gases flow characteristics in micro-channels. It's concluded in the available papers that the entrance effect causes significant difference. An experimental system of s...Entrance region may have important effect on gases flow characteristics in micro-channels. It's concluded in the available papers that the entrance effect causes significant difference. An experimental system of single-phase gas flow characteristics in microchannels was set up. Flow characteristics of nitrogen in PEEK polymer micro-tube (hydraulic diameter is 553btm) was studied experimentally. According to the data of nitrogen flow in the micro-tube with the length ranging from 0. 1m to1.524m, it is shown that the friction constant becomes higher when the tube becomes shorter. By using pipe cutting methods, it's confirmed that entrance effect is one of the key factors that cause friction constant higher than conventional theory. It's found that friction constant of fully developed flow is lower than the value predicted by conventional theory in turbulent region. The result indicates that the flow transition occurs at Reynolds number ranging from 1600-2000. The phenomenon of obvious early transition is not found.展开更多
CFD models have been developed to investigate the Iongwall goaf gas flow patternsunder different mining and geological control conditions.The Iongwall goaf wastreated as porous regions and gas flow was modelled as a m...CFD models have been developed to investigate the Iongwall goaf gas flow patternsunder different mining and geological control conditions.The Iongwall goaf wastreated as porous regions and gas flow was modelled as a momentum sink added to themomentum equation.Gas desorption from the caved goaf and destressed coal seamswithin the mining disturbed area was modelled as additional mass sources in the continuityequation.These CFD models were developed according to specific Iongwall layoutsand calibrated against field monitoring data.Two case studies were presented demonstratingthe application of CFD modelling of goaf gas flow characteristics for improved goafgas capture and the reduction of oxygen ingress into the goaf areas for self-heating prevention.Results from the case studies indicate that the optimum goaf drainage strategywould be a combination of shallow (near the face) and deep holes to improve the overalldrainage efficiency and gas purity.For gassy Iongwall faces retreating against the seam dip,it is recommended to conduct cross-measure roof hole drainage targeting the fracturedzones overlying the return corner,rather than high capacity surface goaf drainage deep inthe goaf.展开更多
基金supported by the THPCCsupported by the National Natural Science Foundation of China (50676047 and 50736003)
文摘Gas flow characteristics in nanopores were investigated experimentally and numerically using molecular dynamics (MD) simulations with an emphasis on the friction factor and gas viscosity. The results show that the viscosity and the friction factor in nanopores are much lower than those in macroscale channels. The actual viscosities obtained from the MD studies showed that the gas viscosity in nanopores is less than the macroscale viscosity because collisions between gas molecules are less frequent in high Knudsen number flows and there are more collisions with the wall. The MD simulations show that the velocity profile is composed of two parts, with a much steeper velocity gradient near the wall.
基金supported by National Natural Science Foundation of China(Grant No.21276241)etc
文摘Gate valve has various placements in the practical usages.Due to the effect of gravity,particle trajectories and erosions are distinct between placements.Thus in this study,gas-solid flow properties and erosion in gate valve for horizontal placement and vertical placement are discussed and compared by using Euler-Lagrange simulation method.The structure of a gate valve and a simplified structure are investigated.The simulation procedure is validated in our published paper by comparing with the experiment data of a pipe and an elbow.The results show that for all investigated open degrees and Stokes numbers(St),there are little difference of gas flow properties and flow coefficients between two placements.It is also found that the trajectories of particles for two placements are mostly identical when St << 1,making the erosion independent of placement.With the increase of St,the distinction of trajectories between placements becomes more obvious,leading to an increasing difference of the erosion distributions.Besides,the total erosion ratio of surface T for horizontal placement is two orders of magnitudes larger than that for vertical placement when the particle diameter is 250 μm.
基金supported by the National Natural Science Foundation of China (No. 50776006)"863" plan (No. 2006AA05Z228)Technological Innova tion Fund of Excellent Doctoral Candidate of Beijing Jiaotong University (No. 48013)
文摘Entrance region may have important effect on gases flow characteristics in micro-channels. It's concluded in the available papers that the entrance effect causes significant difference. An experimental system of single-phase gas flow characteristics in microchannels was set up. Flow characteristics of nitrogen in PEEK polymer micro-tube (hydraulic diameter is 553btm) was studied experimentally. According to the data of nitrogen flow in the micro-tube with the length ranging from 0. 1m to1.524m, it is shown that the friction constant becomes higher when the tube becomes shorter. By using pipe cutting methods, it's confirmed that entrance effect is one of the key factors that cause friction constant higher than conventional theory. It's found that friction constant of fully developed flow is lower than the value predicted by conventional theory in turbulent region. The result indicates that the flow transition occurs at Reynolds number ranging from 1600-2000. The phenomenon of obvious early transition is not found.
文摘CFD models have been developed to investigate the Iongwall goaf gas flow patternsunder different mining and geological control conditions.The Iongwall goaf wastreated as porous regions and gas flow was modelled as a momentum sink added to themomentum equation.Gas desorption from the caved goaf and destressed coal seamswithin the mining disturbed area was modelled as additional mass sources in the continuityequation.These CFD models were developed according to specific Iongwall layoutsand calibrated against field monitoring data.Two case studies were presented demonstratingthe application of CFD modelling of goaf gas flow characteristics for improved goafgas capture and the reduction of oxygen ingress into the goaf areas for self-heating prevention.Results from the case studies indicate that the optimum goaf drainage strategywould be a combination of shallow (near the face) and deep holes to improve the overalldrainage efficiency and gas purity.For gassy Iongwall faces retreating against the seam dip,it is recommended to conduct cross-measure roof hole drainage targeting the fracturedzones overlying the return corner,rather than high capacity surface goaf drainage deep inthe goaf.
