Principal characteristics of turbulent gas-particulate flow in the vicinity of single tube and tube bundle structure

Abstract

In this paper the particle rebounding characteristics of a gas–particle flow over a cylindrical body and an in-line tube bundle arrangement is investigated. With the aid of both experimental and numerical approaches, the mean particulate flow patterns, comprising both incident and rebound particles resulting from the impact of particles on solid walls, are examined. In the experimental investigation, a two-dimensional laser-Doppler anemometry (LDA) technique is used in the immediate vicinity of the body surface to measure the instantaneous incident and rebound particle velocities. The Reynolds-averaging Navier–Stokes equations are solved for the continuum gas phase and the results are used in conjunction with a Lagrangian trajectory model to predict the particle-rebound characteristics. For the single tube model, the experimental observations, also confirmed through computations, reveal a particle rebound zone where the mean particulate flow pattern is significantly modified due to the contribution of the rebound particles during the process of particle-wall impact interaction. This particle rebound zone is found to be a function of mainly the Stokes number (particle inertia), and to a lesser extent on the fluid Reynolds number (gas flow condition) except for high gas flow velocities. For the in-line tube bundle model, particles being rebounded from the first row of tubes at upstream migrated downstream and impinged the other tubes in an extremely complex and random disposition. Detailed measurements on the flow and turbulent characteristics within the subset containing two cylindrical tubes representing the flow over the first and second row tubes in the tube bundle configuration revealed that the heavier particles possessed higher axial and transverse velocity fluctuations than the gas and lighter particles. A means of quantifying the erosion rate using a semi-empirical relationship and CFD approach is presented. The erosion distributions were found to be significantly different between the lighter and heavier particles. Analysis of the effect of the above-mentioned parameters on the rebounding particle flow characteristics and their interrelationship has provided a better understanding on the behaviour of particulate flow impinging on a solid wall body or series of solid bodies. The usefulness of employing the experimental and computational approaches to quantify the particle-wall impact interaction phenomena in this study provides the basis for additional investigations to be undertaken to better comprehend the particulate behaviour in tube bundle structure, for example staggered tube arrangement commonly found in many commercial heat exchangers.