To date, many models have been developed to calculate the flow field in the structured packing by the computational fluid dynamics （CFD） technique, but little experimental work has been carried out to serve the vali...To date, many models have been developed to calculate the flow field in the structured packing by the computational fluid dynamics （CFD） technique, but little experimental work has been carried out to serve the vali-dation of flow simulation. In this work, the velocity profiles of single-phase flow in structured packing are measured at the Reynolds numbers of 20.0, 55.7 and 520.1, using the laser Doppler velocimetry （LDV）. The time-averaged and instantaneous velocities of three components are obtained simultaneously. The CFD simulation is also carried out to numerically predict the velocity distribution within the structured packing. Comparison shows that the flow pattern, velocity distribution and turbulent kinetic energy （for turbulent flow） on the horizontal plane predicted by CFD simulation are in good agreement with the LDV measured data. The values of the x-and z-velocity components are quantitatively well predicted over the plane in the center of the packing, but the predicted y-component is sig-nificantly smaller than the experimental data. It can be concluded that experimental measurement is important for further improvement of CFD model.展开更多
Purpose: To examine the reliability of scanning laser-doppler flowmetry (SLDF) in measuring capillary flow in regions of the optic nerve head which are manifested differently by con-focal tomographic angiography. Perf...Purpose: To examine the reliability of scanning laser-doppler flowmetry (SLDF) in measuring capillary flow in regions of the optic nerve head which are manifested differently by con-focal tomographic angiography. Perfused and non-perfused regions of glaucomatous optic nerves and documented related altitudinal visual field defects were compared using SLDF. Methods: The optic nerve head capillary blood flow was measured in 16 eyes of 13 glaucoma patients with moderate to severe visual field defect.展开更多
Laser Doppler Anemometer has been used to measure the flow field characteristics near the interface around a moving bubble in the presence of ultrafine particles. In order to model a moving bubble, the bubble was fixe...Laser Doppler Anemometer has been used to measure the flow field characteristics near the interface around a moving bubble in the presence of ultrafine particles. In order to model a moving bubble, the bubble was fixed into the counter flow liquid by a metal mesh. Experimental materials are air and water, and the particles are complex oxidate powder. Experiments were carried out under the operating conditions: the liquid flow velocity u 0 is 12.6 cm/s, the equivalent diameter d e is 0.6 cm, the mass concentration of particle is 0.2 0 0 ,the average particle diameter is about 10 nm and the density is 2 g/cm 3. The velocity profiles of both frontal and tail vortex areas were measured respectively. The experimental results show that the velocity fields are obviously changed in the existence of particles. In the frontal area of the bubble, both tangential and normal velocities decrease due to the presence of particles, but in tail vortex area, the tangential velocities increase remarkably, and normal velocities rise gradually from the center towards the fringe in the opposite tendency to that of no particles. The influences of flow field change in the presence of particles on gas liquid mass transfer are analyzed and discussed.展开更多
The measurements of the mean streamwise and radial velocities,the associated turbulence and the relative particle densities were made in an air-solid two-phase flow in a square sectioned (30mm×30mm)90°vertic...The measurements of the mean streamwise and radial velocities,the associated turbulence and the relative particle densities were made in an air-solid two-phase flow in a square sectioned (30mm×30mm)90°vertical to horizontal bend using laser Doppler velocimetry.The radius ratio of the bend was 2.0.Glass beads of 100μm in diameter were employed to form the solid phase.The measurements of air and solid phases were performed separately at the same bulk velocity 19.34m/s,corresponding to a Reynolds number of 3.87×10~4.The mass ratio of solid to air was 1.6%.The results indicate that the particle trajectories are very close to straight lines. The streamwise velocity profiles for the gas and the solids cross over near the outer wall with the solids having the higher speed.At θ=30°and 45°,particle-wall collisions happen mostly in the region from θ=30°to θ=75°,and cause a sudden change in solid velocity.The particles tend to move towards the outer wall in 90° bend.The particle concentration near the outer wall is much higher than that near the inner wall in the bend, and there are few particles in the inside of the bend.The bend leads to apparent phase separation:atθ=45°, the solids concentrate in the half of the duct near the outer wall.Afterθ=60°the second peak concentration appears,and goes gradually towards the inner wall.展开更多
基金Supported by the National Natural Science Foundation of China （No.20476072）.
文摘To date, many models have been developed to calculate the flow field in the structured packing by the computational fluid dynamics （CFD） technique, but little experimental work has been carried out to serve the vali-dation of flow simulation. In this work, the velocity profiles of single-phase flow in structured packing are measured at the Reynolds numbers of 20.0, 55.7 and 520.1, using the laser Doppler velocimetry （LDV）. The time-averaged and instantaneous velocities of three components are obtained simultaneously. The CFD simulation is also carried out to numerically predict the velocity distribution within the structured packing. Comparison shows that the flow pattern, velocity distribution and turbulent kinetic energy （for turbulent flow） on the horizontal plane predicted by CFD simulation are in good agreement with the LDV measured data. The values of the x-and z-velocity components are quantitatively well predicted over the plane in the center of the packing, but the predicted y-component is sig-nificantly smaller than the experimental data. It can be concluded that experimental measurement is important for further improvement of CFD model.
文摘Purpose: To examine the reliability of scanning laser-doppler flowmetry (SLDF) in measuring capillary flow in regions of the optic nerve head which are manifested differently by con-focal tomographic angiography. Perfused and non-perfused regions of glaucomatous optic nerves and documented related altitudinal visual field defects were compared using SLDF. Methods: The optic nerve head capillary blood flow was measured in 16 eyes of 13 glaucoma patients with moderate to severe visual field defect.
文摘Laser Doppler Anemometer has been used to measure the flow field characteristics near the interface around a moving bubble in the presence of ultrafine particles. In order to model a moving bubble, the bubble was fixed into the counter flow liquid by a metal mesh. Experimental materials are air and water, and the particles are complex oxidate powder. Experiments were carried out under the operating conditions: the liquid flow velocity u 0 is 12.6 cm/s, the equivalent diameter d e is 0.6 cm, the mass concentration of particle is 0.2 0 0 ,the average particle diameter is about 10 nm and the density is 2 g/cm 3. The velocity profiles of both frontal and tail vortex areas were measured respectively. The experimental results show that the velocity fields are obviously changed in the existence of particles. In the frontal area of the bubble, both tangential and normal velocities decrease due to the presence of particles, but in tail vortex area, the tangential velocities increase remarkably, and normal velocities rise gradually from the center towards the fringe in the opposite tendency to that of no particles. The influences of flow field change in the presence of particles on gas liquid mass transfer are analyzed and discussed.
文摘The measurements of the mean streamwise and radial velocities,the associated turbulence and the relative particle densities were made in an air-solid two-phase flow in a square sectioned (30mm×30mm)90°vertical to horizontal bend using laser Doppler velocimetry.The radius ratio of the bend was 2.0.Glass beads of 100μm in diameter were employed to form the solid phase.The measurements of air and solid phases were performed separately at the same bulk velocity 19.34m/s,corresponding to a Reynolds number of 3.87×10~4.The mass ratio of solid to air was 1.6%.The results indicate that the particle trajectories are very close to straight lines. The streamwise velocity profiles for the gas and the solids cross over near the outer wall with the solids having the higher speed.At θ=30°and 45°,particle-wall collisions happen mostly in the region from θ=30°to θ=75°,and cause a sudden change in solid velocity.The particles tend to move towards the outer wall in 90° bend.The particle concentration near the outer wall is much higher than that near the inner wall in the bend, and there are few particles in the inside of the bend.The bend leads to apparent phase separation:atθ=45°, the solids concentrate in the half of the duct near the outer wall.Afterθ=60°the second peak concentration appears,and goes gradually towards the inner wall.
