The traditional fixed-bed reactor design is usually not suitable for the low tube-to-particle diameter ratios(N = D/d b 8) where the local phenomena of channeling near the wall and backflow in the bed are dominant. Th...The traditional fixed-bed reactor design is usually not suitable for the low tube-to-particle diameter ratios(N = D/d b 8) where the local phenomena of channeling near the wall and backflow in the bed are dominant. The recent"solid particle" meshing method is too complicated for mesh generation, especially for non-spherical particles in large random packed beds, which seriously hinders its development. In this work, a novel high-fidelity mesh model is proposed for simulation of fixed bed reactors by combining the immersed boundary and adaptive meshing methods. This method is suitable for different shapes of particles, which ingeniously avoids handling the complex "contact point" problem. Several packed beds with two different shapes of particles are investigated with this model, and the local flow in the bed is simulated without geometrical simplification. The predicted pressure drop across the fixed bed and heat transfer of the single particle are in good agreement with the corresponding empirical relations. Compared with spherical particles, the packed bed packing with pentaphyllous particles has lower pressure drop and better heat/mass transfer performance, and it shows that this method can be used for the screening of particle shapes in a fixed bed.展开更多
For microfluidic systems, interfacial phenomena in micro-reactors are of great importance because they control the transfer and reaction characteristics. This paper dwells on how the surface property and geometry infl...For microfluidic systems, interfacial phenomena in micro-reactors are of great importance because they control the transfer and reaction characteristics. This paper dwells on how the surface property and geometry influence the mass flux in a complex microchannel. The lattice Boltzmann method(LBM) with a pseudo potential model and the Shan–Chen model for the interaction between fluid and hydrophobic surface were built up, so a boundary slip effect was added and verified. On this basis, a microchannel with variable-section geometry was simulated. The results indicate that the optimal design and the flow pattern are quite different under hydrophilic and hydrophobic conditions. A microchannel with sequential hydrophilic and hydrophobic surface was also simulated. The numerical results indicate that the hydrophobic wall can improve the mass flux, irrespective of microchannel geometry. Particularly, an empirical correlation with a linearly relationship between length of hydrophobic segment and mass flux was obtained for the straight microchannel.展开更多
基金Supported by the National Key Research and Development Program(2016YFB0301702)National Natural Science Foundation of China(21490584,21878298,91534105)+2 种基金Major National Scientific Instrument and Equipment Development Project(21427814)Key Research Program of Frontier Sciences of CAS(QYZDJ-SSW-JSC030)Jiangsu National Synergetic Innovation Center for Advanced Materials.
文摘The traditional fixed-bed reactor design is usually not suitable for the low tube-to-particle diameter ratios(N = D/d b 8) where the local phenomena of channeling near the wall and backflow in the bed are dominant. The recent"solid particle" meshing method is too complicated for mesh generation, especially for non-spherical particles in large random packed beds, which seriously hinders its development. In this work, a novel high-fidelity mesh model is proposed for simulation of fixed bed reactors by combining the immersed boundary and adaptive meshing methods. This method is suitable for different shapes of particles, which ingeniously avoids handling the complex "contact point" problem. Several packed beds with two different shapes of particles are investigated with this model, and the local flow in the bed is simulated without geometrical simplification. The predicted pressure drop across the fixed bed and heat transfer of the single particle are in good agreement with the corresponding empirical relations. Compared with spherical particles, the packed bed packing with pentaphyllous particles has lower pressure drop and better heat/mass transfer performance, and it shows that this method can be used for the screening of particle shapes in a fixed bed.
基金Supported by National Key Research and Development Program(2016YFB0301701)the National Natural Science Foundation of China(21276256,21490584,91534105)
文摘For microfluidic systems, interfacial phenomena in micro-reactors are of great importance because they control the transfer and reaction characteristics. This paper dwells on how the surface property and geometry influence the mass flux in a complex microchannel. The lattice Boltzmann method(LBM) with a pseudo potential model and the Shan–Chen model for the interaction between fluid and hydrophobic surface were built up, so a boundary slip effect was added and verified. On this basis, a microchannel with variable-section geometry was simulated. The results indicate that the optimal design and the flow pattern are quite different under hydrophilic and hydrophobic conditions. A microchannel with sequential hydrophilic and hydrophobic surface was also simulated. The numerical results indicate that the hydrophobic wall can improve the mass flux, irrespective of microchannel geometry. Particularly, an empirical correlation with a linearly relationship between length of hydrophobic segment and mass flux was obtained for the straight microchannel.
