Investigation of the fouling layer growth using coupled immersed boundary and Eulerian-Lagrangian methods

Abstract

This study presents a numerical simulation of fouling, focusing on the complex, unsteady, multiphase, and turbulent process of fouling layer growth on the outer surface of a heat exchanger's pipe. Addressing the fundamental challenges associated with fouling phenomenon, an Eulerian-Lagrangian approach is employed, wherein the Eulerian method calculates continuous phase flow parameters, such as velocity and pressure, and the Lagrangian method precisely tracks particles near the surface. The immersed boundary method is utilized to simulate fouling layer growth without altering the underlying grid, effectively reducing computational cost compared to dynamic mesh methods. The model is validated against experimental data involving ash particle deposition on a cylindrical surface. Key parameters, including Young's modulus, Reynolds number, and particle size distribution, are systematically analyzed. The findings reveal that particles smaller than 10 micrometers can penetrate the rear of the cylinder, while larger particles (25-30 micrometers) predominantly accumulate on the front, exhibiting nearly double the deposition frequency compared to smaller particles. As particle diameter increases, both Young's modulus and flow velocity contribute to a reduced settling rate by lowering the critical deposition velocity. A higher Reynolds number results in a 67 % reduction in fouling mass due to decreased adhesive velocity and enhanced particle detachment. Additionally, larger particles tend to migrate towards the edges of the heat exchanger tube, promoting a more uniform surface distribution. Notably, at elevated Young's modulus values (e.g., 50,000 MPa), particle deposition on the surface is virtually eliminated.