关键词: 气-固两相流, 纤维表面, 黏性颗粒, 滚动摩擦系数, 颗粒捕集

Abstract: Numerous researchers focus on the simulation of factors affecting particle deposition and agglomeration within the fiber, while few researchers have paid attention to the changes in the coefficient of rolling friction between the particles on particle deposition and agglomeration. To simplify the process of calculating the fiber filtration media model is also limited to the circular regular arrangement of the fiber model, and if the fiber model and the actual filter media have a lower degree of conformity, the difference between the simulation results and the actual test results will be larger.
In this paper, by observing and analyzing the surface morphology and structural characteristics of polyester fibers with round, triangular and cruciform cross sections, a three-dimensional fiber model with a fiber diameter of 5 μm, an SVF of 9%, and randomly distributed cross sections of round and triangular fibers in space was established by using Digimat fiber modeling software. Based on the CFD-DEM coupling method, the JKR contact model was introduced under the laminar flow field to analyze the changes of the filtration mechanism of the particles during the motion process, the influence of the changes of the rolling friction coefficient between the particles on the deposition characteristics of the viscous particles inside the fibers with different cross-sectional shapes, and the influence of the fiber cross-sectional shapes on the particles trapping efficiency.
The filtration mechanism of particles in the process of time-varying movement changes, and in the early stage of filtration, the number of particles produced is small, mainly relying on the fiber itself to capture particles, while surface filtration plays a dominant role; in the late stage of filtration, most of the particles are accumulated in the windward side of the fiber to form a cluster of dendritic particles, and the filtration mechanism changes to a portion of the capture by the fiber itself, with the other portion of the dendritic particles being deposited in the fiber cluster. The other part is captured by the dendritic particles that have been deposited on the fibers, which is captured by the filter cake formed by the fiber, i.e. "dust filtering dust". When the inter-particle rolling friction coefficient is less than 0.05, the inter-particle adhesion is small, the relative sliding between the particles increases, and the particles adhering to the windward side of the fiber force chain structure are in a non-straightened state; when the inter-particle rolling friction coefficient is greater than 0.05, the inter-particle rolling damping force will increase with the rolling friction coefficient, and then the inter-particle chain of force is more stable, the resistance of the bending performance is greatly increased, and the chain of force structure tends to be longer and straighter, reducing the particles' resistance to bending due to the rolling friction coefficient, reducing the chance of particles falling due to collision, and increasing the number of inter-particle adhesion. The increase of inter-particle rolling friction will increase the inter-particle normal elastic force and adhesion force, the inter-particle interaction is more close, and the number of mutually adhesive particles will also increase; in the three cross-sectional shape fiber model, the number of fibers trapping the viscous particles as a whole increases with the increase of the coefficient of inter-particle rolling friction. At the early stage of filtration, the rolling friction coefficient has less influence on the number of captured particles because the number of released particles is small and the chance of collision between particles is small. With the filtration and the increase of the number of released particles, the collision rate between particles becomes larger, the rolling damping between particles with large rolling friction coefficient increases, the force chain structure formed between particles is more stable, the increase of the normal force makes it more difficult for particles to slip after collision, and the more number of particles adheres to the particles; the number of particles captured is larger than the number of circular and triangular cross-section fibers because of the raised and groove structure of the surface of the cross-shaped fibers, and the specific surface area of triangular cross-section fibers is larger than the number of particles captured by the cross-shaped fibers. The specific surface area of fibers with triangular cross-section is larger than that of fibers with circular cross-section, and the number of particles captured is higher than that of fibers with circular cross-section.

Key words: gas-solid two phases flow, fiber surface, viscous particles, coefficient of rolling friction, particle trapping