Search

• Separated flow around the perforated tube is studied experimentally. • The void fraction in the wake region is independent of the inlet liquid flow rate. • The flow pattern contributes to the variation of air separation efficiency. • The separation parameters can be predicted using minimum kinetic energy principle. Gas-liquid separator plays an important role in the reactor fission gas removal system. Utilizing the differential pressure formed by flow around the perforated tube, the separator achieves gas–liquid separation, meanwhile having advantages such as simple structure. The evolution characteristics of gas–liquid interface and the variation of parameters such as separation efficiency and pressure drop under plug flow and slug flow are investigated. The void fraction in wake region is only related to the inlet volumetric fraction. The variation of air separation efficiency with inlet volumetric fraction is influenced by the inlet flow pattern, and the separation purity increases with the inlet volumetric fraction. The prediction methods of air separation efficiency, pressure drop and other parameters based on Weber number and liquid phase Reynolds number are obtained in accordance with dimensional analysis and minimum kinetic energy principle with the prediction accuracy within ±20 %, which provides guidance for practical application and optimization. [ABSTRACT FROM AUTHOR]

In this study, we investigate computationally the low-Reynolds-number droplet motion in a square micro-channel, a problem frequently encountered in microfluidic devices, enhanced oil recovery and coating processes. The droplet deformation and motion are determined via a three-dimensional spectral boundary element method for wall-bounded flows. The effects of the flow rate, viscosity ratio and droplet size on the interfacial dynamics are identified for droplets smaller and larger than the channel size and for a wide range of viscosity ratio. Owing to the stronger hydrodynamic forces in the thin lubrication film between the droplet interface and the solid walls, large droplets exhibit larger deformation and smaller velocity. Under the same average velocity, a droplet in a channel shows a significantly smaller deformation and higher velocity than in a cylindrical tube with the same size, owing to the existence of the corners' area in the channel which permits flow of the surrounding fluid. A suitable periodic boundary implementation for our spectral element method is developed to study the dynamics of an array of identical droplets moving in the channel. In this case, the droplet deformation and velocity are reduced as their separation decreases; the reduction is influenced by the flow rate, viscosity ratio and more significantly the droplet size. [ABSTRACT FROM AUTHOR]

The hemodynamic forces on endothelial cells or leukocytes attached to the inner surface of blood vessels affect the physiological behavior of these systems via mechano-transduction or receptor-ligand binding. The present study investigates the relative importance and nature of the two components of the hemodynamic force, i.e., the shear and normal force, on a cell and its vicinity. We consider a wide range of blood vessels (from capillaries to arteries) and cell’s spreading angles. Based on computational investigation and analysis, our study demonstrates that the normal force contributes significantly to the total force on the cell; the influence is much more pronounced in small vessels. We also show that the spreading of the cell on the vessel surface should not be discounted, especially in small vessels. Our results are also applicable to the fluid forces on other protuberances of biological nature attached to vascular vessels (e.g., cancer cells and biofilm) as well as to the fluid forces over protuberances in microfluidics and porous media. [ABSTRACT FROM AUTHOR]

In the present study we describe a novel three-dimensional spectral boundary element algorithm for interfacial dynamics in Stokes flow and/or gravity. The main attraction of this approach is that it exploits all the benefits of the spectral methods (i.e., exponential convergence and numerical stability) with the versatility of the finite element method. In addition, it is not affected by the disadvantage of the spectral methods used in volume discretization to create denser systems. Our algorithm also exploits all the benefits of the boundary element techniques, i.e., a reduction of the problem dimensionality and great parallel scalability. To achieve continuity of the interfacial geometry and its derivatives at the edges of the spectral elements during the droplet deformation, a suitable interfacial smoothing is developed based on a Hermitian-like interpolation. An adaptive mesh reconstructing procedure based on the relevant lengths of the spectral elements is also described. In addition, we consider the inertialess motion of a buoyant droplet left to rise (or sediment) near a vertical solid wall and compare our numerical results with analytical predictions. In our study we emphasize the need for computational studies for the accurate determination of droplet migration near solid walls. [ABSTRACT FROM AUTHOR]

In this study, we experimentally investigate the large-scale vortex pair formed by droplets in the spanwise direction of the flow field of a hollow cone spray injected transversely into a gaseous crossflow. Experiments are conducted in a square channel for a wide range of spray and crossflow conditions. The spatial and velocity distributions of the spray droplets for different cross-sections of the flow field in terms of different flow conditions are measured through flow visualization. Three parameters, namely, vortex vorticity, depth of vortex core, and distance between both vortex cores, are used to characterize the counter-rotating vortex pair (CVP) formed by droplets. The crossflow Reynolds number, (initial atomized) droplet Reynolds number, and number of droplets injected per unit time are all found to significantly influence the features of droplets CVP. We newly define the spray-to-crossflow momentum flux ratio ( J ∗) based on the injected momentum flux of initial atomized droplets. Accordingly, we develop a set of correlations for predicting the features of droplets CVP based on experimental measurements and the Buckingham π theorem. The results show that these correlations well predict all measured conditions. The results of this study should provide insights into the dynamics of spray droplets in a crossflow and an understanding of the large-scale mixing between a hollow cone spray and a crossflow. [ABSTRACT FROM AUTHOR]