To find out the detailed characteristics of the coherent structures and associated particle dispersion in free shear flow, large eddy simulation method was adopted to investigate a two-dimensional particleladen wake f...To find out the detailed characteristics of the coherent structures and associated particle dispersion in free shear flow, large eddy simulation method was adopted to investigate a two-dimensional particleladen wake flow. The well-known Sub-grid Scale mode introduced by Smagorinsky was employed to simulate the gas flow field and Lagrangian approach was used to trace the particles. The results showed that the typical large-scale vortex structures exhibit a stable counter rotating arrangement of opposite sign, and alternately form from the near wall region, shed and move towards the downstream positions of the wake with the development of the flow. For particle dispersion, the Stokes number of particles is a key parameter. At the Stokes numbers of 1.4 and 3.8 the particles concentrate highly in the outer boundary regions. While the particles congregate densely in the vortex core regions at the Stokes number of 0. 15, and the particles at Stokes number of 15 assemble in the vortex braid regions and the rib regions between the adjoining vortex structures.展开更多
Kinetic knowledge is of great importance in achieving good control of the pyrolysis and gasification process and optimising system design. An overall kinetic pyrolysis scheme is therefore addressed here. The ki-net...Kinetic knowledge is of great importance in achieving good control of the pyrolysis and gasification process and optimising system design. An overall kinetic pyrolysis scheme is therefore addressed here. The ki-netic modelling incorporates the following basic steps: the degradation of the virgin biomass materials into pri-mary products ( tar, gas and semi-char), the decomposition of primary tar into secondary products and the continuous interaction between primary gas and char. The last step is disregarded completely by models in the literature. Analysis and comparison of predicted results from different kinetic schemes and experimental data on our fixed bed pyrolyser yielded very positive evidence to support our kinetic scheme.展开更多
Strongly swirl flow simulation are still under deve1oping. In this paper, ε equation based on the Renormalization. Group theory is used into algebraic stress model. Standard κ-ε model, algebraic stress model by Jia...Strongly swirl flow simulation are still under deve1oping. In this paper, ε equation based on the Renormalization. Group theory is used into algebraic stress model. Standard κ-ε model, algebraic stress model by Jiang Zhang[5]. and present model (RNG-ASM) are applied simultaneously to simulating the confined strongly swirling flow. The Simulating results by RNG-ASM model are compared to the results by other two model, it is shown that the predictions by this model display reasonable agreement with experimental data, and lead to gnater improvement than Zhang’s ASM turbulence model[5].展开更多
Particle Imaging Velocimetry (PIV) is a valuable measuring tool for studyingmultiphase flows, such as liquid-gas and gas-solid flow. It can be used to carry out manyhydrodynamic studies, in particular, to determine ac...Particle Imaging Velocimetry (PIV) is a valuable measuring tool for studyingmultiphase flows, such as liquid-gas and gas-solid flow. It can be used to carry out manyhydrodynamic studies, in particular, to determine accurately the gas solid flow structure in CFB(Circulating Fluidized Beds). In this paper, the technique characteristics was described in applyingthe PIV to measure the gas-solid flow in circulating fluidized beds. A primary experiment wascomple-ted on a CFB unit with the PIV, yielding the velocity vector fields of high-density particlesfor different gas-solid superficial velocities and solid recycle rates. Velocities of thetransported particles were calculated with cross-correlation method. The major factors influencingthe successful measurement of particle velocity with the PIV technique were also described.展开更多
文摘To find out the detailed characteristics of the coherent structures and associated particle dispersion in free shear flow, large eddy simulation method was adopted to investigate a two-dimensional particleladen wake flow. The well-known Sub-grid Scale mode introduced by Smagorinsky was employed to simulate the gas flow field and Lagrangian approach was used to trace the particles. The results showed that the typical large-scale vortex structures exhibit a stable counter rotating arrangement of opposite sign, and alternately form from the near wall region, shed and move towards the downstream positions of the wake with the development of the flow. For particle dispersion, the Stokes number of particles is a key parameter. At the Stokes numbers of 1.4 and 3.8 the particles concentrate highly in the outer boundary regions. While the particles congregate densely in the vortex core regions at the Stokes number of 0. 15, and the particles at Stokes number of 15 assemble in the vortex braid regions and the rib regions between the adjoining vortex structures.
文摘Kinetic knowledge is of great importance in achieving good control of the pyrolysis and gasification process and optimising system design. An overall kinetic pyrolysis scheme is therefore addressed here. The ki-netic modelling incorporates the following basic steps: the degradation of the virgin biomass materials into pri-mary products ( tar, gas and semi-char), the decomposition of primary tar into secondary products and the continuous interaction between primary gas and char. The last step is disregarded completely by models in the literature. Analysis and comparison of predicted results from different kinetic schemes and experimental data on our fixed bed pyrolyser yielded very positive evidence to support our kinetic scheme.
文摘Strongly swirl flow simulation are still under deve1oping. In this paper, ε equation based on the Renormalization. Group theory is used into algebraic stress model. Standard κ-ε model, algebraic stress model by Jiang Zhang[5]. and present model (RNG-ASM) are applied simultaneously to simulating the confined strongly swirling flow. The Simulating results by RNG-ASM model are compared to the results by other two model, it is shown that the predictions by this model display reasonable agreement with experimental data, and lead to gnater improvement than Zhang’s ASM turbulence model[5].
文摘Particle Imaging Velocimetry (PIV) is a valuable measuring tool for studyingmultiphase flows, such as liquid-gas and gas-solid flow. It can be used to carry out manyhydrodynamic studies, in particular, to determine accurately the gas solid flow structure in CFB(Circulating Fluidized Beds). In this paper, the technique characteristics was described in applyingthe PIV to measure the gas-solid flow in circulating fluidized beds. A primary experiment wascomple-ted on a CFB unit with the PIV, yielding the velocity vector fields of high-density particlesfor different gas-solid superficial velocities and solid recycle rates. Velocities of thetransported particles were calculated with cross-correlation method. The major factors influencingthe successful measurement of particle velocity with the PIV technique were also described.
