Capturing the instantaneous flow structure in gas-solid circulating fluidized bed using high-speed imaging and fiber optic sensing

2019 ◽  
Vol 207 ◽  
pp. 713-724 ◽  
Author(s):  
Xiaoyang Wei ◽  
Jesse Zhu
Keyword(s):  
Fluidized Bed ◽  
Flow Structure ◽  
High Speed ◽  
Fiber Optic ◽  
Circulating Fluidized Bed ◽  
High Speed Imaging ◽  
Instantaneous Flow ◽  
Fiber Optic Sensing

Transient Computational Fluid Dynamics/Discrete Element Method Simulation of Gas–Solid Flow in a Spouted Bed and Its Validation by High-Speed Imaging Experiment

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Ling Zhou ◽  
Lingjie Zhang ◽  
Weidong Shi ◽  
Ramesh Agarwal ◽  
Wei Li
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Discrete Element Method ◽  
Fluidized Bed ◽  
High Speed ◽  
Discrete Element ◽  
Bubble Shape ◽  
High Speed Imaging ◽  
Bed Height ◽  
Simulation Results

A coupled computational fluid dynamics (CFD)/discrete element method (DEM) is used to simulate the gas–solid two-phase flow in a laboratory-scale spouted fluidized bed. Transient experimental results in the spouted fluidized bed are obtained in a special test rig using the high-speed imaging technique. The computational domain of the quasi-three-dimensional (3D) spouted fluidized bed is simulated using the commercial CFD flow solver ANSYS-fluent. Hydrodynamic flow field is computed by solving the incompressible continuity and Navier–Stokes equations, while the motion of the solid particles is modeled by the Newtonian equations of motion. Thus, an Eulerian–Lagrangian approach is used to couple the hydrodynamics with the particle dynamics. The bed height, bubble shape, and static pressure are compared between the simulation and the experiment. At the initial stage of fluidization, the simulation results are in a very good agreement with the experimental results; the bed height and the bubble shape are almost identical. However, the bubble diameter and the height of the bed are slightly smaller than in the experimental measurements near the stage of bubble breakup. The simulation results with their experimental validation demonstrate that the CFD/DEM coupled method can be successfully used to simulate the transient gas–solid flow behavior in a fluidized bed which is not possible to simulate accurately using the granular approach of purely Euler simulation. This work should help in gaining deeper insight into the spouted fluidized bed behavior to determine best practices for further modeling and design of the industrial scale fluidized beds.

Three-dimensional flow structure and string cavitation in a fuel injector and their effects on discharged liquid jet

2019 ◽  
Vol 22 (1) ◽  
pp. 243-256 ◽  
Author(s):  
Rubby Prasetya ◽  
Akira Sou ◽  
Junichi Oki ◽  
Akira Nakashima ◽  
Keiya Nishida ◽  
...  
Keyword(s):  
Vortex Ring ◽  
Flow Structure ◽  
High Speed ◽  
Three Dimensional ◽  
Liquid Jet ◽  
Fuel Injector ◽  
High Speed Imaging ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Stereo Particle Image Velocimetry

Two kinds of cavitation may occur in mini-sac type diesel injectors. The first is geometrical cavitation, which can usually be seen as a film-like structure in the nozzle. The second is the filament-like string cavitation. Both types of cavitation are known to affect fuel spray characteristics, although the effects of geometrical cavitation and that of string cavitation have not been individually clarified. Moreover, the mechanism behind string cavitation occurrence is still unclear. String cavitation usually occurs at low needle lift, which might indicate the existence of a vortex ring flow in the sac. However, because of the difficulty in precise flow measurement of the three-dimensional flow structure in the sac, the link between vortex ring flow and string cavitation occurrence in the sac has not been proven. In this study, high-speed imaging of string cavitation, geometrical cavitation, and discharged liquid jet of an enlarged three-hole mini-sac diesel fuel injector was conducted to individually clarify the effects of string cavitation and geometrical cavitation on the discharged liquid jet angle. Furthermore, tomographic–stereo particle image velocimetry was carried out on the sac. The experiments were conducted at two different needle lifts, to clarify the link between needle lifts and flow structure in the sac, as well as how it affects string cavitation occurrence and liquid jet angle. The results confirmed that at low needle lift, vortex ring flow forms in the sac, which may induce helical flow in the nozzle, resulting in a large jet angle. Vortex strength varies with time, and string cavitation occurs when the vortex is particularly strong. As a result, the magnitude of the jet angle increase at low needle lift is enhanced when string cavitation occurs. At high needle lift, flow pattern in the sac becomes relatively uniform, which makes it harder for string cavitation to form.

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