Immersed boundary method for simulations of erosion on staggered tube bank by coal ash particles

Abstract

To predict the erosion of tubes and surfaces of heat exchangers in boilers caused by coal ash particles, particle-laden flows past a 10×11 staggered tube bank in a duct are investigated using a high-resolution numerical technique. The flow field is obtained through direct numerical simulation (DNS), the coupling between tubes and underlying flow is done through the immersed boundary method, and the particles are tracked by the Lagrangian approach. Classic particle–wall impact and erosion models are incorporated to investigate the collision and wear on the side walls and the tubes near the bottom side walls of the duct. It is found that particles at different Stokes numbers have different dispersion patterns in the flow field, and lead to different characteristics of collision and erosion on the near-wall tubes as well as the side walls. The larger Stokes number results in higher global erosion on the first tube near the side wall, but the particles with St=1.0 cause the largest erosion to other downstream tubes because of the preferential concentration effect. The distributions of collision and erosion on each tube are not uniform, but bias toward the side facing the wall, and the more downstream tubes have the higher erosion. For side wall erosion, particles having higher local collision frequency may lead to lower erosion. The reverse trend is also observed for the particles with the intermediate Stokes number of 1. Periodical oscillation of particle–wall collision and erosion happens because of the staggered arrangement of the tubes.