Numerical investigation on non-steady-state filtration of elliptical fibers for submicron particles in the ‘‘Greenfield gap’’ range

Abstract

While noncircular fibers (especially elliptical fibers) have demonstrated significant advantage of high collection efficiency for fine particles, only a few investigations have yet been conducted to study the non-steady-state filtration performance of noncircular fibers during the particle deposition process. In this work, we utilize a lattice Boltzmann-cellular automata (LB-CA) probabilistic model to investigate the growing process of particle dendrites on elliptical fibers. The transient pressure drop and collection efficiency are analyzed. For the deposition of sub-micron particles (0.3–0.5µm in the “Greenfield gap’’ range) which are dominated by the diffusion and interception mechanism, the captured particles distribute relatively uniformly around elliptical fibers (the equivalent diameter df of 22.8µm and the packing density of 5% in this work) at the initial stage of loading process. The deposited particle leads to the formation of complicated dendrites, expanding the filtration area and thereby altering the flow field. Then particles will mostly deposit on the windward of the elliptical fibers (especially on the both ends of the elliptical long axis) at the complete dendrites capture stage. Various operation conditions (inlet flow velocity of 0.1–0.3m/s, particle diameter of 0.3–0.5µm, aspect ratio of elliptical fibers of 2–4, orientation angle of 30°~60°) are simulated. It is found that the pressure drop of dust loaded elliptical fibers normalized by the corresponding pressure drop of clean elliptical fibers increases almost exponentially with the mass of captured particles; and the normalized collection efficiency of elliptical fibers is approximately a linear function of the deposit mass when the increase rate of the normalized efficiency is stabilized.