The spatial relationship between the energy dissipation slabs and the vortex tubes is investigated based on the direct numerical simulation（DNS） of the channel flow. The spatial distance between these two structures...The spatial relationship between the energy dissipation slabs and the vortex tubes is investigated based on the direct numerical simulation（DNS） of the channel flow. The spatial distance between these two structures is found to be slightly greater than the vortex radius. Comparison of the core areas of the vortex tubes and the dissipation slabs gives a mean ratio of 0.16 for the mean swirling strength and that of 2.89 for the mean dissipation rate. These results verify that in the channel flow the slabs of intense dissipation and the vortex tubes do not coincide in space. Rather they appear in pairs offset with a mean separation of approximately 10η.展开更多
The entropy balance equation that describes the entropy budget of atmospheric systems is derived from the Gibbs relation.The distribution of the entropy flows of a west-Pacific typhoon and a Bengal-Bay cyclone is calc...The entropy balance equation that describes the entropy budget of atmospheric systems is derived from the Gibbs relation.The distribution of the entropy flows of a west-Pacific typhoon and a Bengal-Bay cyclone is calculated and thus the dissipativity of the atmospheric systems is revealed.展开更多
Collision among particles plays a significant role in governing the structure of gas-solids flow in a riser, especially in the dense and acceleration region. The inter-particle collision is the major cause not only fo...Collision among particles plays a significant role in governing the structure of gas-solids flow in a riser, especially in the dense and acceleration region. The inter-particle collision is the major cause not only for the kinetic energy dissipation （in terms of additional pressure drop beyond the solids hold-up） but also for the control of solids acceleration （in terms of a balancing force to prevent a free acceleration of solids）. A neglect of the balancing force of inter-particle collision against the hydrodynamic force in the solids momentum equation would simply overestimate the solids acceleration or concentration while underestimate the axial gradient of pressure along the riser by a large margin, typically by up to two orders of magnitude. This paper aims to illustrate the importance of the collision on the characteristic of the gas-solids riser flow. Our analysis shows that the collision force should be of the same order of magnitude as that of the drag force in the dense and acceleration region, which can be far beyond that of gravitational force on solids. A simple formulation of the collision force is therefore proposed to bear a similar format of drag force, with regard to the dependence upon local solids properties.With the inclusion of the proposed correlation of collision force in the solids momentum equation, our model would be able to yield reasonable phase distributions of gas-solid flows, which can be validated, in a bulk range, against available measurements of solids volume fraction and axial gradient of pressure.展开更多
基金Project supported by the National Natural Science Foun-dation of China(Grant No.51127006)
文摘The spatial relationship between the energy dissipation slabs and the vortex tubes is investigated based on the direct numerical simulation（DNS） of the channel flow. The spatial distance between these two structures is found to be slightly greater than the vortex radius. Comparison of the core areas of the vortex tubes and the dissipation slabs gives a mean ratio of 0.16 for the mean swirling strength and that of 2.89 for the mean dissipation rate. These results verify that in the channel flow the slabs of intense dissipation and the vortex tubes do not coincide in space. Rather they appear in pairs offset with a mean separation of approximately 10η.
文摘The entropy balance equation that describes the entropy budget of atmospheric systems is derived from the Gibbs relation.The distribution of the entropy flows of a west-Pacific typhoon and a Bengal-Bay cyclone is calculated and thus the dissipativity of the atmospheric systems is revealed.
文摘Collision among particles plays a significant role in governing the structure of gas-solids flow in a riser, especially in the dense and acceleration region. The inter-particle collision is the major cause not only for the kinetic energy dissipation （in terms of additional pressure drop beyond the solids hold-up） but also for the control of solids acceleration （in terms of a balancing force to prevent a free acceleration of solids）. A neglect of the balancing force of inter-particle collision against the hydrodynamic force in the solids momentum equation would simply overestimate the solids acceleration or concentration while underestimate the axial gradient of pressure along the riser by a large margin, typically by up to two orders of magnitude. This paper aims to illustrate the importance of the collision on the characteristic of the gas-solids riser flow. Our analysis shows that the collision force should be of the same order of magnitude as that of the drag force in the dense and acceleration region, which can be far beyond that of gravitational force on solids. A simple formulation of the collision force is therefore proposed to bear a similar format of drag force, with regard to the dependence upon local solids properties.With the inclusion of the proposed correlation of collision force in the solids momentum equation, our model would be able to yield reasonable phase distributions of gas-solid flows, which can be validated, in a bulk range, against available measurements of solids volume fraction and axial gradient of pressure.
