Numerical simulation of nano and micro-droplets captured on a single fiber with different orientations

The capture of entrained droplets from a gas flow can be performed to a large extent using cyclone operation, but the smallest droplets can only be collected in a separate separation step using fibrous filter systems. In reduced-order models, the macroscopic collection efficiency of these filters is often taken independently of the fiber orientation, which prohibits the tailoring and optimization of the fiber structures. To fill the gap in the research on the effect of fiber orientation on droplet capture efficiency, in this work, we investigate how the fiber angle influences the droplet capture effectivity from a gas flow through numerical simulations for low Stokes numbers (ranging from 0.01–1.3), in order to improve macroscopic models. This study provides theoretical guidance for optimizing fiber arrangements in filters, facilitating the application in separation and filtration technologies. Using numerical simulations, we study various first-principle droplet capture mechanisms, using fibers with different orientations with respect to the entraining gas flow. We describe the implementation of the numerical method, based on the OpenFOAM framework, which incorporates the Cunningham correction factor, Stokes drag, and Brownian motion correction, and we use the model to investigate the capture efficiency of droplets in the size range 200 nm—1.8 µm. The model predicts the droplet capture efficiency as a function of the fiber orientation and Stokes number, and we propose an empirical correlation applicable to droplet capture dominated by the diffusion, interception, and inertial impaction mechanisms. Our work therefore also serves as a stepping stone towards the simulation of full fibrous systems in which varying orientations of fibers are ubiquitous. • The fiber orientation significantly affects the droplet capture efficiency. • The OpenFOAM model incorporates the Cunningham correction factor and Brownian motion force for an accurate prediction of droplet capture. • An empirical correlation for the droplet capture efficiency was developed based on the fiber orientation and the Stokes number.