scholarly journals Visualizing Water Desaturation in Frozen Gas Diffusion Layers With Flow Field Segmentation via Synchrotron X-Ray Radiography

2021 ◽  
Vol 9 ◽  
Author(s):  
Yuzhou Zhang ◽  
Ryan Anderson ◽  
Ning Zhu ◽  
Lifeng Zhang
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Water Distribution ◽  
Gas Flow ◽  
Cold Start ◽  
Gas Diffusion ◽  
Water Transfer ◽  
X Ray ◽  
Transfer Behavior ◽  
Field Geometry

Synchrotron X-ray tomography images were used to study dynamic, regional water transfer behavior in the gas diffusion layer (GDL) during thawing and desaturation processes. Initially saturated, frozen GDLs were thawed and desaturated with air in a serpentine gas flow channel. On-the-fly (OTF) high speed CT scans via synchrotron X-ray allowed the capture of consecutive water transfer inside the GDL under the cold start-up gas purging condition. Desaturation data of Sigracet 35AA GDLs with three superficial gas velocities (2.88–5.98 m/s) were selected for analysis. Multiple spatial segmentation levels based on the flow field geometry, including channel vs. rib, individual channels and ribs, and smaller sections in each channel and rib, were applied to the in-plane direction to study the GDL regional thawing and desaturation behaviors. Each segmentation volume had a similar desaturation pattern in general; however, water distribution and desaturation show heterogeneity over the GDL domain, as well as relation with factors including the flow field geometry, air traveling distance, and initial saturation level. These data from the segmentation analysis expand the knowledge of localized water transfer behavior during the cold start thawing process. These data can also provide valuable information for future cold start modeling and help in optimizing the PEM fuel cell flow field design.

A Stochastic Immersed Model of Breakup Characteristics in Dense Air Atomization Flow Field

2020 ◽  
Author(s):  
Tian Deng ◽  
Xingming Ren ◽  
Yaxuan Li
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Large Scale ◽  
Gas Flow ◽  
Liquid Core ◽  
Average Diameter ◽  
Simulation Method ◽  
Spray Angle ◽  
Random Structure ◽  
Momentum Ratio

Abstract For the low-speed liquid injected into the high-speed strong turbulent gas flow in the same direction, the atomization is a transient-intensive spray, and there are many factors affecting and controlling the atomization. In this paper, the distribution and characteristics of the liquid breakup in the air atomized flow field are analyzed. A stochastic immersed model to simulate the liquid core is developed, in which, the liquid core is regarded as an immersed porous medium with a random structure, and the probability of existence is used to simulate the position of the liquid core. The initial fragmentation mechanism of the air blast atomization is applied as the global variables of the stochastic process. Using the above stochastic immersed model, combined with the Large Eddy Simulation method, the numerical simulation of the downstream flow field of a coaxial jet air atomizing nozzle is carried out. Additional force is added to the momentum equation in the LES model. Instantaneous air velocity at the air-liquid interface is characterized by instantaneous liquid phase velocity at the same time. The size of the initial atomized droplet satisfies a probability distribution, and once the large droplets are formed, the Lagrangian method is used to track the droplets. The comparison between the simulation results and the experimental results shows that this stochastic immersed model can quickly capture the information of length and position of the liquid nucleus. When the gas-liquid momentum ratio M is 3∼10000, the liquid core length can be predicted more accurately. When M>10, the prediction result is much better than phenomenological model. This model is capable of capturing flow field structures such as recirculation zones and large-scale vortices. The results of initial spray angle from experiment expression give slightly better agreement with this model. Increasing the momentum ratio leads to decreasing of the initial spray angle. The particle size of the droplets near the nozzle can be accurately predicted, especially when the gas velocity is large (bigger than 60 m/s), and the average diameter prediction error of the droplets is less than 10%.

A Method for Solving Problems of Irrotational Gas Flow by Means of High-Speed Digital Computers

1957 ◽  
Vol 24 (4) ◽  
pp. 497-500
Author(s):  
Toyoki Koga
Keyword(s):  
Flow Field ◽  
Analytical Methods ◽  
High Speed ◽  
Gas Flow ◽  
Fundamental Equation ◽  
Numerical Procedure ◽  
The State ◽  
Two Dimensional ◽  
Perfect Gas ◽  
Irrotational Flow

Abstract A numerical procedure is proposed for solution of certain problems in steady gas flow where subsonic, sonic, and supersonic regions appear simultaneously. The difficulties that occur in analytical methods for taking into account the differences of the type of the fundamental equation (elliptic, parabolic, hyperbolic) are avoided. Given a streamline and the state of the gas along that streamline, the co-ordinates of the neighboring streamline and the state of the gas along it can be computed. The procedure can be applied successively to cover a flow field. The method is described in detail for two-dimensional, steady, irrotational flow (without shocks) of a perfect gas, and an example is given.

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